v>EPA
United States
Environmental Protection
Agency
Global Positioning Systems
Technical Implementation
Guidance
180ODC02.RPT
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EPA/600/R-02/031
April 2000
Global Positioning Systems -
Technical Implementation Guidance
Contributors:
Tim Bridges, Region 11
George M. Brilis1'2
David Burden6 7
Chad Cross1 2
Ivan DeLoatch1 3
Timothy Drexler, Region 51
Michael Glogower, Region 21
Dan Harris, Region 71
Karl Hermann, Region 81
Patricia Hirsch1 5
Cheryl Itkin12
Linda Kirkland1 3
Noel Kohl, Region 51
Shashank Kalra13
Carrie Middleton1 4
Nita Tallent-Halsell1 2
Michelle Torreano1 3
Jonathan Vail, Region 41
Patricia A. Willis, Region 61
1 U.S. Environmental Protection Agency (EPA)
2 Office of Research and Development (ORD)
3 Office of Environmental Information (OEI)
4 National Enforcement Investigations Center (NEIC)
5 Office of General Counsel (OGC)
6 U.S. Department of the Interior (DOI)
7 Bureau of Reclamation (BoR)
Project Lead
George M. Brilis, Chair
U.S. EPA Geospatial Quality Council
U.S. Environmental Protection Agency
Office of Research and Development
Environmental Sciences Division
Human Exposure Research Branch
Post Office Box 93478
Las Vegas, Nevada 89193-3478
180ODC02.RPT
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In memory of
Mason J. Hewitt
Mr. Mason J. Hewitt joined the Environmental Protection Agency (EPA) in March 1987. His was asked to
direct and manage the EPA Office of Research and Development's Las Vegas Laboratory's Geographic
Information Systems (GIS). Mr. Hewitt was instrumental in working with EPA Headquarters, Regional
offices, and other agencies in developing GIS software and standardizing computer programs. Mr. Hewitt
became nationally and internationally known for his expertise in the GIS world.
Mr. Hewitt also served on the EPA advisory panel for the Global Position System (GPS). This panel
developed EPA accuracy standards for the GPS to be used for georeference corrections and to meet
Topographic Mapping Standards.
Mr. Hewitt died of injuries suffered from an accident in 1996. His leadership and inspiration has made an
impact on the conservation of our environment for many years to come. The EPA has established the
Mason J. Hewitt GIS Award in recognition for development of outstanding GIS tools within the EPA
during each calendar year. All recipients have their names engraved on the trophy, which is held by the
individuals or team for one year. The trophy is then presented to the next award recipients.
Mr. Hewitt laid the foundation for the harmonization of the EPA's approach to GPS data collection and
use. He put pen to paper, and it is upon those publications that this work is based.
As a scientist, Mr. Hewitt maintained records so that those who followed him could continue his work. As
a husband and father, Mr. Hewitt always put his family first. As a patriot, Mr. Hewitt was entrusted by
our country to keep vigilance over our nation's safety. As a friend, he is irreplaceable.
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Notice
The information in this document has been funded (wholly or in part) by the United States Environmental
Protection Agency. It has been subjected to Environmental Protection Agency review. Mention of trades
names or commercial products does not constitute endorsement or recommendation for use.
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Foreword
The U.S. Environmental Protection Agency (EPA) has long employed data of spatial orientation in pursuit
of its mission to understand and protect the environment. For years, these data were applied in standard
cartographic presentation techniques, either via hand drawn or digital transposition from a source map. In
either case, the map developer or analyst had the ability during this transposition to apply decision rules of
logical consistency to make the map "right," shift, and offset map elements so that their relationships to
each other did not violate inherent rules of consistency (e.g., streets did not cross buildings; city boundaries
followed the delimiting streets). These adjustments and the inaccuracies introduced in the transposition
process may or may not be considered viable, depending upon whether these adjustments and errors
exceeded traditional map accuracy standards.
Regardless of the acceptability of these errors, they are virtually undetectable to the decision maker or
technical analyst, who is presented with a map product. The nature of these errors in hard copy maps is
attributable to the medium itself, which is not amenable to overlay and comparison analysis. More often
than not, mapped data are presented in its own singular context, with few other types of spatially-correlated
data simultaneously presented. However, with the advent of Geographic Information Systems (GIS),
digital spatial data sets are generated and stored independently and then combined in analysis, making
differences in resolution and accuracy of spatial data visually detectable. Although each separate data set
may not violate its own accuracy standard, the use of these differing maps may produce a composite map
that is perceived to be flawed. Recognizable inconsistencies may or may not detract from the accuracy of
the spatial analysis of interest, depending upon the nature of the analysis. At a minimum, they possibly
detract from the credibility of the analysis product.
Global Positioning Systems (GPS), originating from the U.S. military programs, have great potential for
ameliorating these types of problems as well, making errors easier to detect. With the ability to locate
features with an accuracy of a few meters, this technology essentially lowers the detection limit for
positional accuracy at low cost. Indeed, the U.S. National Geodetic Survey acknowledges that the
accuracy of GPS positioning may exceed the accuracy of some benchmarks in the National Geodetic
Reference System (NGRS) (National Geodetic Survey, 1990). Previously, cadastral surveys, which are
relatively expensive, were considered to be the only highly accurate positioning system.
GPS technology is now enjoying many civilian sector applications. With this increasing demand, not only
is the cost of units going down, but a tremendous amount of development effort is being applied toward
increasing their portability, accuracy, and ease of data integration with popular mapping system
applications. Proposals have been made within the EPA to establish networks of survey base stations that
would offer complete coverage of a Regional jurisdiction for roving GPS units. Such proposals shed light
on the potential future for the use of GPS by the EPA. By integrating GPS into the Agency's regulatory
data collection efforts, benefits in improved spatial analysis resolution could result in "lighter" solutions in
protection, causation, and restoration decision making. Eliminating the range of uncertainty in positional
data may offer opportunities for cost savings.
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In comparison to highly accurate GPS data, the relative acceptability of the EPA's existing spatial data, in
terms of resolution and accuracy, diminishes. Locational methods previously employed may no longer be
suitable for applications and analysis that require the most rigorous spatial data quality available. The
EPA has been aware of the locational errors in Agency-sponsored data collection efforts. And as the
Agency seeks to integrate geographic analysis as part of its operations, these locational errors become
apparent and many times embarrassing. In order to address this error source, the EPA has adopted a
Locational Data Policy (LDP). The purpose of the LDP is to "ensure the collection of accurate,
consistently formatted, fully documented locational coordinates in all relevant data collection activities
pursuant to the EPA's mission (LDPGD, 1991)." In order to support the accuracy target specified within
the LDP, the policy endorses GPS as the technology of choice. Collecting highly accurate GPS data
requires careful planning. Once collected, consideration and thoughtful treatment of the data must be given
vis-a-vis in its use with data of substantially lower accuracy. This guidance document seeks to provide
GPS users with information and guidance on this technology and its potential use in Agency applications.
This foreword was, in large part, derived from the parent document published by Mason J. Hewitt III et al.,
and is a testament to the timelessness of his work.
George M. Brilis, Chair
EPA Geospatial Quality Council
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Table of Contents
Notice iii
Foreword iv
Background ix
Acknowledgments x
Authors xi
Peer Reviewers xi
Organizational Acronyms xi
Section I Introduction 1
Purpose of Document and Intended Audience 1
Document Contents 2
Section II Alternative Methods of Geopositioning 4
Conventional Surveying 4
Methods of Point Surveying 5
Section III Global Positioning System (GPS) Technology 6
Methods of Satellite Positioning 9
Autonomous 9
Differential 9
GPS and GIS 10
Section IV Quality Assurance Considerations 11
Overview of QA Project Plan Requirements for Geospatial Data 11
Graded Approach 12
EPA QA Requirements 12
Project Design Criteria 13
Accuracy and Precision 13
Factors Affecting the Accuracy of the GPS Survey 14
Multipath 14
Atmospheric Delays 14
Baseline Length 15
Position Dilution of Precision (PDOP) 15
Signal-to-Noise Ratio (SNR) 15
Data Quality Indicators and General Requirements 15
Accuracy and Precision Requirements 15
Multipath Avoidance Requirements 16
Metadata File Collection Requirements 16
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Table of Contents, Continued
Satellite Detection and Position Requirements 16
Atmospheric and Ratio Requirements 17
Base Station Distance Requirements 17
Calibration Requirements 17
Completeness Requirements 18
Data Collection Time and Frequency Requirements 18
Data Evaluation 18
Section V Core Elements of GPS Standard Operating Procedures 19
Planning and Preparation 19
Planning and Implementing a GPS Survey 19
Pre-survey Planning 19
Define Objectives of Survey 20
Define Project Area 20
Determine Observation Window and Schedule Operations 20
Establish Control Configuration 21
Select Survey Locations 22
Equipment Logistics 22
Reconnaissance 23
Locate and Verify Control Point Locations 23
Preview Instrument Locations 23
Physically Establish Point Locations 23
Survey Execution 23
Establishing a Schedule of Operations 23
Pre-survey: The Day Before 23
Pre-data Collection: Establishing a Base Station 24
Data Collection: Performing the GPS Survey 24
Returning from the Field 24
Data Transfer 24
Initial Processing 25
Computation 25
Data Conversion to GIS 25
Documentation and Reporting 26
Section VI Management of Locational Data 27
Section VII Legal Considerations 30
Collection of Data 30
Storage and Maintenance of Data 30
Release of Data Pursuant to Freedom of Information Act Requests 30
Privacy Concerns 31
A-110 31
Data as Confidential Business Information 32
Toxics Release Inventory (TRI) 32
Locational Data as Intellectual Property 32
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Table of Contents, Continued
Section VIII References 33
Appendix A Glossary of GPS Terms 36
Appendix B U.S. EPA - Locational Data Policy 38
Appendix C Examples of GPS in Environmental Applications 43
Appendix D IRM Policy Manual 2100 CHG 2 45
Pre-survey Checklist 50
VIM
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Background
The U.S. EPA Geospatial Quality Council (GQC) was formed in 1998 to provide Quality Assurance
guidance for the development, use, and products of geospatial activities and research. The long-term goals
of the GQC are expressed in a living document, currently the EPA Geospatial Quality Council Strategy
Plan, FY-02, EPA/600/R-01/063. The GQC is approaching the development of guidance and technical
documents in the flow order of the Geospatial Information Lifecycle. The first two major products of the
GQC are: a training course GISfor QA Professionals, which can be located at
http://www.epa.gov/Region06/6en/gis-qa/index.htm. and the EPA QA Guidance for Developing
Geospatially-related Quality Assurance Projects, EPA/600/R-01/062. It is important to note that the
GQC operates without a budget.
A survey conducted jointly by the EPA Data Acquisition Branch (DAB) of the Office of Information
Collection in the Office of Environmental Information and the GQC determined that the approach to GPS
data collection and disposition throughout the EPA was inconsistent. GQC literature research determined
that existing documents were technically outdated and did not address legal considerations, data
disposition, and information management. This document is intended to fill that gap and be treated as a
living document by its organizational custodian.
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Acknowledgments
This document reflects the efforts of the U.S. EPA Geospatial Quality Council (GQC). Members of the
GQC that contributed to this effort originated from EPA Regions, Program Offices, the EPA QA Staff, the
Office of Environmental Information, and the Office of Research and Development. The GPS Technical
Subgroup of the EPA GIS WorkGroup played an essential role in the development of this document as did
the U.S. Bureau of Reclamation. These scientists and professionals dropped their organizational ties and
worked together in a seamless manner to harmonize the approach used to collect GPS data.
The foundation of this document is based on GIS Technical Memorandum 3: Global Positioning Systems
and its Application in Environmental Programs, R. Puterski, J. A. Carter, M. J. Hewitt III (Project
Officer), H. F. Stone, L. T. Fisher, and E. T. Slonecker, EPA/600/R-92/036, February 1992. This
document was refreshed by the GPS Technical SubGroup of the EPA GIS WorkGroup in 2000. The GQC
began its work from a solid foundation of documents and devoted professionals.
Manuscript reviewers provide the critical function of peer review. Their comments, suggestions, and
recommendations for this document are greatly appreciated.
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Authors
Tim Bridges
EPA, Region 1
George M. Brilis
EPA, ORD
David Burden
DOI, BoR
Chad Cross
EPA, ORD
Ivan DeLoatch
EPA, OEI
Timothy Drexler
EPA, Region 5
Karl Hermann
EPA, Region 8
Patricia Hirsch
EPA, OGC
Cheryl Itkin
EPA, ORD
Shashank Kalra
EPA, OEI
Noel Kohl
EPA, Region 5
Carrie Middleton
EPA, NEIC
Michelle Torreano
EPA, OEI
Jonathan Vail
EPA, Region 4
Patricia A. Willis
EPA, Region 6
Peer Reviewers
Michael Glogower
EPA, Region 2
Dan Harris
EPA, Region 7
Nita Tallent-Halsell
EPA, ORD
Organizational Acronyms
EPA U.S. Environmental Protection Agency
ORD Office of Research and Development
OEI Office of Environmental Information
NEIC National Enforcement Investigations Center
OGC Office of General Counsel
DOI U.S. Department of the Interior
BoR Bureau of Reclamation
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Section I
Introduction
Purpose of Document and Intended Audience
As outlined in the Locational Data Improvement Project Plan (1996), the United States Environmental
Protection Agency (U.S. EPA, hereinafter referred to as the "Agency" or the "EPA" for the purposes of
this document) has developed this manual to guide the process of collecting, editing, and exporting accurate
spatial data using the Global Positioning System (GPS). Each Region will develop their own Standard
Operation Procedures (SOP) manual on the regional specific GPS data collection procedures.
The intended audience of this document includes U.S. EPA staff, contractors and grantees who will be:
1. Involved in the planning of a GPS survey
2. Conducting a GPS survey
3. Maintaining and lending GPS equipment
4. Responsible for processing data sets collected in the field and their conversion to various file formats
for use in a Geographic Information System (GIS) database.
This technical implementation guidance will serve as a reference guide for Agency staff, which will be
using GPS equipment, and also the individual(s) responsible for the maintenance of this equipment.
Training on the proper use of the GPS equipment maintained by the regional offices will be required of
Agency staff, contractors, and grantees prior to its use. Training will be provided either by Agency staffer
through vendor contracts.
This document will not attempt to detail the specific functions of the various receivers since the rapid
advancements in GPS technology would necessitate constant, diligent updates to this document. Receiver
operating procedures will be covered during training sessions through the use of separate documents. The
mention of trade names or commercial products does not constitute endorsement or recommendation for
use.
Four important points must be understood by the readers and users of this document:
1. The level of effort and detail should be based on a common sense, graded approach that establishes
QA and QC requirements commensurate with the importance of the work, the available resources,
and the unique needs of the organization.
2. Since this is intended to be a living document, recommendations to include technology that is cur-
rently being developed, and new technology that has not yet become an integral part of the EPA's
toolbox, were not included in the document. When the new technology has become an integral part
of the EPA's geospatial repertoire, this document will be updated by its custodian (OEI).
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3. This document is not intended to "micromanage" the GPS community, therefore, suggestions to
define limits were excluded. In addition, attempts were made to keep the document "user-friendly"
by keeping the volume of the document to a minimum.
4. Users should check the appropriate references for the latest updates, such as the EPA Locational
Data Policy, prior to the initiation of work.
Document Contents
A brief overview of the GPS system and the procedures involved in acquiring consistently accurate GPS
locational data sets is provided below.
The EPA has long employed information of a spatial nature in the analysis of environmental problems.
This information was traditionally applied using standard cartographic techniques such as hand drawn
maps and other graphic presentations. Advances in Geographic Information Systems (GIS) have
automated the management of spatial data as well as most of the presentation functions (e.g., map
production) previously done by hand. Until recently, however, GIS systems relied primarily on
transposing, or digitizing, spatial data from existing hard copy maps.
The Global Positioning System (GPS) is a worldwide, satellite-based system with location positioning
capabilities. The system is administered and managed by the Department of Defense. It is comprised of:
• a space segment of approximately 24 operational satellites in complimentary orbits,
• a ground control segment made up of a network of control stations around the globe, and
• a users segment, which includes anyone who uses GPS to collect locational information.
The system utilizes precise time and radio signals to determine distances from satellites to user GPS
receivers. Distances are most commonly calculated by using the time it takes for a radio signal code to be
transmitted from the satellite and received by the GPS unit. Precise time is critical to the successful
operation of the system. The control stations ensure that the satellites employ synchronized, atomic clock-
derived universal time coordinates (UTC), commonly known as Greenwich Mean Time (GMT). Receiver
units collecting four satellite signals can determine the geodetic (x, y, z) location through a process of
mathematical triangulation. The satellite signals contain precise time and satellite position information.
GPS technology is used as a method of accurately determining the coordinates of point locations. The
three-dimensional position, or the x, y, and z geodetic coordinates, are determined for the point locations;
however, only the x and y values are primarily used. This is due to the processes involved in the system;
the vertical GPS coordinates are approximately half as accurate as the horizontal GPS coordinates. The
position reported by the GPS unit is based on the geodetic model selected. The vertical, or z coordinate,
value is not as accurate as the reported position due to the geometry of the satellite constellation relative to
the receivers position on the earth.
Utilization of accurate x, y, and z coordinates in a geographic information system is the primary purpose
for most GPS use in the Agency. GPS is one of the arrays of tools for accurately determining location in
the field. The collection of x, y, and z coordinates (for gross data collection) for locations in the field using
GPS is useful for a variety of purposes, including accurate sample locations, locational correlation of
remotely sensed data with ground truth locations, and efficiently collecting better spatial data for USEPA's
information management.
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The accuracy required for GPS data collection will vary depending on the reasons for gathering locational
information. Different equipment and procedures are needed to identify the outline of a landfill than those
needed to determine the location of a monitor well used for a hydrological survey. GPS equipment
accuracies can range from about 13 meters (one standard deviation and up to 22 meters at two standard
deviations) of horizontal accuracy in a mapping grade unit to a 1-2 cm of vertical and horizontal accuracy
in a survey grade unit (note that 1-2 cm vertical accuracy is attainable under conducive environmental
conditions, using high quality instrumentation, and exercising skillful operation of the GPS receiver).
However, all of these units have a place in the Agency and some elements of GPS use are common to all
units and procedures.
Generally, the quality of coordinate information (GPS data) is dependent on the quality of equipment, the
understanding and skill of the operator of the GPS receiver, and the signals and factors affecting the signals
broadcast by the GPS satellites. Since GPS utilizes high frequency radio waves, interferences with the
satellite signals can and do occur. The user may or may not be aware of these, so steps must be taken to
minimize the impacts on data quality. Within this document, users will be made aware of tools such as
averaging a series of points based on repeated measurements, using higher quality GPS receivers, recording
quality information, and using comparisons of the GPS generated coordinates with other georeferenced
sources in order to minimize accuracy errors. Alternative field methods are provided to cope with most
interferences while providing acceptable results.
Most GPS data collection work includes: project planning and GPS equipment preparation; determination
of remote reception points; labeling and identification of point locations; operation of the GPS receivers;
dealing with interferences; downloading the collected data to a personal computer; making backup and
archival copies of the data files on diskettes; post processing of the data files, if needed, to perform
differential correction and averaging of location samples; conversion of the data to GIS format; and the
maintenance of the GPS units.
Documentation and proper reporting of what the data represent and method collection are critical to the
successful utility of the information. The data documentation, or metadata, should capture the type and
description of the location collected, the coordinate units and reference datums, and the method of location
determination. These "metadata" are required by the EPA Locational Data Policy and the Federal
Geographic Data Committee's (FGDC) Locational Metadata Standard, which is an executive order to
which EPA is obligated to comply.
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Section II
Alternative Methods of Geopositioning
Conventional Surveying
GPS is a valuable tool for use with other surveying techniques whether they are cadastral, topographic or
geodetic. GPS is valuable for rapidly acquiring position, but other techniques may be used for parcel
definition and recording, topographic surface generation, and geodetic modeling. GPS does not totally
replace any of the other techniques. In particular, GPS is not always used to generate topographic
surfaces. However, it is being used to reference topographic surfaces generated by other methods to a real-
world coordinate system. In many cases, GPS is being used to reference boundaries established by other
survey techniques to real-world coordinates, and it is very valuable in updating the horizontal and vertical
control of the geodetic network.
Where GPS is particularly effective for surveying is in locating site locations, sampling transects, and
approximating boundaries between or along features. In addition, it can be used to approximate travel
speed between points and travel distance, and the rate of sampling along the vector traveled.
There has been, and will continue to be, a considerable and rapid evolution in geopositioning techniques
and technologies, as evidenced by the emergence of systems like GPS. Many of the older, traditional
positioning survey methods are being supplemented, and in some cases, replaced by advanced
geopositioning systems. These older survey methods tend to require more field time, are highly labor
intensive, and are costly per feature identified. Although conventional surveying is still appropriate for
high accuracy requirements in localized, accessible study areas, these older methods are best used in
concert with other more advanced and cost-effective techniques. Topographic, cadastral, and geodetic
surveys are perhaps the three types of conventional surveying most impacted by advanced technologies like
GPS.
Topographic surveys determine the elevation heights and contours of land surfaces. These surveys also
serve to locate buildings, roads, sewers, wells, and water and power lines. The U.S. Geological Survey
(USGS) has historically conducted topographic surveys in order to produce topographic maps at a scale of
1:24,000. These maps provide an excellent base for much of the EPA environmental analysis programs.
As these maps become available in digital form, they are providing an important source of locational and
geographic data for the Agency. Remote sensing techniques in conjunction with GPS and other positional
systems are currently being used to obtain more accurate and detailed surface elevation positional
information for many of these land features.
Cadastral surveys are performed to establish legal and political boundaries, typically for land ownership
and taxation purposes. A boundary survey is a type of cadastral survey which is limited to one specific
piece of property. The U.S. Bureau of Land Management (BLM) relies on cadastral surveying to
determine the legal boundaries of public lands. Published cadastral surveys are of importance to the EPA,
as for instance, where potentially responsible parties (PRPs) and impacted parties on Superfund
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enforcement cases are concerned. GPS already can provide highly accurate positional reference
information for boundary surveys of these types of facilities.
Geodetic surveys (i.e., control surveys) are global surveys made to establish control networks (consisting of
reference or control points) as a basis for accurate land mapping. Geodetic surveys provide quantitative
data on the absolute and relative accuracy of reference positions or physical monuments on the Earth's
surface. The U.S. National Geodetic Survey (NGS) is responsible for establishing a national geodetic
control network for the entire country referenced to a national horizontal datum. NGS also establishes the
vertical datum, the location of mean sea level from which most elevation data are determined or referenced.
Highly accurate EPA geopositioning requirements should be attained with reference to a well defined
geodetic survey or network. All NGS geodetic control points are accessible via the Web
rhttp://www.ngs.noaa.gov1 and are searchable by area as well as site name. In addition, there is a network
of continuously operating reporting stations (CORS) Hittp://www.ngs.noaa.gov/CORS1. The importance
of both the historic and current network is that they provide the underlying basis for all of map data.
In the event that the EPA will require or avail itself of conventional surveying to meet its geopositioning
needs, it is important to understand these techniques, their strengths, and their limitations. The EPA does
and will continue to use products derived from conventional surveying methods. The geopositional
accuracy of the products generated by EPA, USGS, NGS, and BLM can usually be obtained from these
agencies at the time of product acquisition.
Methods of Point Surveying
Global positioning systems technology is one of a number of positioning techniques that have been
developed since the late 1950s and is being used for establishing positions of points on or near the Earth's
surface. Besides GPS, some of the advanced technology systems being utilized for geopositioning and
navigation today include OMEGA, Loran-C, Transit, Inertial Survey Systems (ISS), VHP Omni-
directional Range/Distance Measuring Equipment (VOR/DME), Tactical Air Navigation (TACAN), and
Instrument Landing System (ILS). The U.S. Department of Transportation (DOT), primarily through the
U.S. Coast Guard (USCG) and the Federal Aviation Administration (FAA), is responsible for the
application of these technologies for civil navigation. The U.S. Defense Department (DOD) oversees the
use of these systems for military users.
Inertial Survey Systems (ISS) are self-contained and highly mobile systems that detect relative compass
direction by using gyroscopes. The most effective application of ISS is to measure unknown points that are
located between known control points. ISS may serve some EPA needs where the EPA and/or contractual
personnel are in the field with vehicles that could potentially be equipped with ISS. When ISS is combined
with GIS, they are mutually supportive.
ILS is a passive system used commercially for precision aircraft radar approach navigation. The FAA is
currently investigating the continued use of this geopositioning technology and may recommend
transitioning to a system based on GPS. A similar active system is precision radar (PAR), which is used
mostly by the military. Both systems have a very short range.
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Section III
Global Positioning System (GPS) Technology
The Navigation Satellite Time and Ranging (NAVSTAR) GPS is a system that is operated by the
Department of Defense (DOD) dating back to 1977 with the launch of the first in a series of satellites that
currently orbit approximately 12,500 miles above Earth. There are at least four satellites in each of six
fixed orbiting planes. This constellation provides GPS users with four to eight visible satellite signals at all
times from any point on Earth. Its initial use was intended for highly accurate, all-weather, instantaneous
positioning capabilities for the U.S. military and its allies, but the GPS is also freely available to the public.
Many of the surveillance and monitoring programs of the Agency represent some of the civilian
applications of the GPS. The decreasing cost of increasingly accurate, portable GPS receivers has allowed
this technology to become one of the Agency standards for the acquisition of spatial data.
There are three components of the GPS that allows it to calculate a position:
1. The space segment - At least 24 NAVSTAR satellites, including one acting as a spare.
2. The ground control segment - Five global stations that serve as uplinks to the satellites, making
adjustments as necessary to satellite orbits and clocks.
3. The user segment - The ground-based GPS receiver, which is composed of an antenna, preamplifier,
radio signal microprocessor, control and display device, data recording unit, power supply (GIS
Technical Memorandum 3, 1992), and a clock.
Satellite positioning operates by measuring the time delay of precisely transmitted radio signals from
satellites whose position can be very accurately determined. Furthermore, with the help of a few
fundamental laws of physics, the positions of these satellites as a function of time (their ephemerides) can
be rather easily predicted. By measuring the distances (or range vectors) between a survey point of
unknown location on the surface of the planet and the predicted positions of a number of orbiting satellites,
it is possible to calculate the position of a point.
Trilateration: A GPS receiver operates on the principle of trilateration, whereby a position is calculated
by measuring the distance between the receiver antenna and at least four satellites, which act as precise
reference points. Two questions need to be answered in order to calculate a position using the GPS:
1. How far is your receiver from the satellite?
2. What is the location of the satellite?
These questions will need to be answered simultaneously for at least three satellites to calculate a
two-dimensional position. However, this manual will require the tracking of four satellite signals in order
to calculate a three-dimensional position. The first question of determining the distance between the
receiver and the satellite is referred to as satellite ranging. The simplest way to illustrate this is from the
following example. The reception of one satellite signal establishes the receivers position on the surface of
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a sphere centered around the satellite, with the radius representing the range between the satellite and the
receiver antenna (Figure 1).
One measurement narrows down our
position to the surface of a sphere
We are on the
surface of this
sphere
Figure 1.
The addition of a second signal will place the receivers location somewhere within the shaded intersection
of these two spheres (Figure 2). The intersection of a third sphere, which represents the third satellite
signal, into the two other spheres will reduce the location of the receiver to two possible locations (Figure
3). One of these two points is disregarded as a possible solution because it is either in space or moving at a
high rate of speed. The fourth satellite is used to solve for X, Y, Z and time variables (Figure 4).
The distance between the receiver and the satellites is calculated by multiplying the speed of the radio
signal (speed of light) by the time it takes for the satellite signal to reach the receiver antenna, otherwise
known as the time delay, as discussed above.
A second measurement narrows down our
position to the intersection of two spheres
A third measurement narrows
down our position to two points
The intersection
of two spheres
is a circle
The intersection
of three spheres
is two points
Figure 2.
Figure 3.
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A fourth measurement narrows our
position down to one point
The intersection
of four spheres
Figure 4.
Herein lies the obstacle to satellite ranging: determining exactly when the signal left the satellite in order to
determine the distance between the receiver and the satellite. This is accomplished by correlating a pseudo-
random noise (PRN) code generated by the satellite with the same code being generated internally by the
receiver. Each satellite broadcasts its own
unique PRN code which the receiver recognizes
and looks for each time it is enabled. The
satellite and receiver are synchronized so that
they are generating the PRN code at exactly the
same time. A tracking loop within the receiver
shifts the internal replica of this PRN code in
time until maximum correlation occurs between
the replica code generated by the receiver and
the actual PRN code broadcast by the satellite
(Figure 5) (Leick, 1995). This time shift value
required to align the two code events multiplied
by the speed of light gives a range value from
How do we know when the signal left the satellite?
• Use same code at the receiver and satellite
• Synchronize the satellites and receivers so they are generating same
code at same time
• Then look at the incoming code from the satellite and see how long
ago the receiver generated the same code
measure the time
difference between
the same part of code
from satellite
from ground receiver
J
the observer to the satellite.
Figure 5.
These range values are biased, however, by error inherent in the receivers quartz clock and by the Doppler
effect caused by the motion of the satellite, so the range is referred to as a pseudo-range. The satellites
contain atomic clocks with nanosecond accuracy while the receivers do not possess that capability and any
time difference between the two, even less than a second, would translate into the calculation of an
inaccurate position of hundreds of miles. To overcome this problem, the receiver uses the range
measurements from a fourth satellite to remove the error caused by the clock discrepancies and generates a
three-dimensional position. Essentially, the receiver will adjust the range values until the spheres
representing the range all intersect at one point (Figure 4).
The second question of where each satellite is in space is easily predicted because they are placed in precise
orbits. Since there is no atmospheric drag on the satellite, it remains, for the most part, in this orbit. These
orbits are continuously monitored by the DOD control segment and any deviations in the satellites
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condition, referred to as its ephemeris, are corrected. These ephemerides are in turn, continuously
transmitted by each satellite so the GPS receiver knows the precise location of each satellite at all times. A
better understanding of GPS status and other support information may be found at
www.spacecom.af.mil/usspace/gps support/.
Methods of Satellite Positioning
Autonomous
With the autonomous, or stand-alone method, positions are calculated by one GPS receiver operating at an
unknown location. This method can be very useful for many applications that do not require a high degree
of accuracy. Autonomous receivers are inexpensive, and with the recent decision by the DOD to turn off
Selective Availability, autonomous GPS users have a horizontal accuracy of approximately 13 meters at
one standard deviation and 22 meters at two standard deviations.
Differential
The second method, which is used for higher accuracy GPS data collection and when accurate navigation is
needed, is the differential correction method. Differential GPS (DGPS) refers to the technique used to
improve positioning accuracy by determining the positioning error at a known location and subsequently
incorporating a correction factor into the position calculated by another receiver operating in the same area
while both are tracking the same satellites. This process involves correcting GPS positions gathered by the
roving receiver at an unknown location with GPS positions simultaneously collected at a known location
(the base station). Both the rover and base station must be tracking the same satellite signals for this
method to work, the idea being that the errors impacting the rover are impacting the base station as well.
Since the precise location of the base station has been previously established, usually with sub centimeter
accuracy, a correction factor can be calculated continuously at the base station and applied to the positions
obtained by the rover.
There are two modes of differential correction:
Real Time: Differential correction employs either a radio link between the rover and base station receivers
or subscription to a commercial satellite service such as OmniStar. This method of data collection is
necessary for high accuracy navigation. In the ground-based system, correction factors generated by
the base station are continuously broadcasted to the GPS receiver acting as the rover. These
correction factors are applied almost instantaneously to the uncorrected positions being collected by
the rover receiver. In the satellite-based system, used in areas where transmitting base stations are not
available, a satellite in a geosynchronous orbit transmits the correction.
Post Processed: Post processing is used when high accuracy data is needed, but the effort does not require
real-time high accuracy. Post processing involves the collection of autonomous data with a GPS
receiver acting as the rover, then correcting these data after the survey is completed using post
processing software. It is similar to the real-time method in which a base station and rover receiver
collect GPS data simultaneously from the same subset of satellites. However, there is no need for a
radio link between the two. Post processing software compares GPS data from both the base station
and the rover after the survey is completed, and it performs any necessary corrections. Post processing
is generally available via the web from most GPS receiver manufacturers and other sites. Use of these
sites should occur shortly after the GPS data is collected in the field to be able to match the same time
frame as the data collected in the field.
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Since both the rover and the base station must track the same satellites, they must be within a certain range
of each other. This distance is referred to as the length and ideally should not exceed 300 km (186 mi).
The number of accessible base stations in each Region will most likely increase to keep pace with the
growing public and private sector demand for GPS services.
GPS and GIS
Most of the cost involved in establishing and maintaining a GIS lies in the acquisition of data, both spatial
and tabular. GPS has emerged as an effective tool in the ongoing process of improving data capture
efficiency and accuracy. Positions are collected by the receiver along with attribute information, the extent
of which is dependent upon the sophistication of the receiver, the data logging device, and the needs of the
user. Positions are collected using a variety of receivers and methods (walking, driving, flying).
Positions collected by the GPS receiver are converted to cartographic features:
Points: Collecting positions while a receiver remains stationary.
Lines: Joining of positions in a time sequence; each position acts as a vertex while the receiver is in
motion during data collection.
Polygons: Joining of positions in a time sequence with the last position being connected to the first
position logged, and thereby closing off a line segment.
Along with these spatial features, some GPS data collectors give the user the ability to record tabular data
that can be entered and linked to features by using data dictionaries that are customized to fit the specific
requirements of a survey. Refer to the appropriate users manual for a detailed description of this data
collection tool. After post processing, these features can be exported to a number of GIS formats and used
for analysis with other spatial data.
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Section IV
Quality Assurance Considerations
This guidance supplements EPA Guidance for Quality Assurance (QA) Project Plans (EPA QA/G-5), in
that the focus here is on collection and use of geospatial rather than other environmental data (e.g., strictly
chemical or biological data), including unique aspects of data storage, retrieval, and processing.
The EPA recognizes that the use of quality management components and tools in the Organization/Program
and the Project levels is based on a graded approach where components and tools are applied according to
the scope of the program and/or the intended use of the outputs from a process. This approach recognizes
that a "one size fits all" approach to quality requirements is not appropriate for an organization as diverse
as the EPA.
Overview of QA Project Plan Requirements for Geospatial Data
The U.S. Environmental Protection Agency (EPA) has developed the Quality Assurance Project Plan as an
important tool for project managers and planners to document the type and quality of data needed to make
environmental decisions and to provide a blueprint for collecting and assessing those data. The QA project
plan is the critical planning document for any environmental data collection or use because it documents
how quality assurance (QA) and quality control (QC) activities will be implemented during the life cycle of
a project or task. EPA policy requires that all projects involving the generation, acquisition, and use of
environmental data will be planned and documented and have an Agency-approved QA project plan prior to
the start of data collection. The QA project plan should be detailed enough to provide a clear description of
every aspect of the project and include information for every member of the project staff, including data
collectors, software users, and data reviewers. Effective implementation of the plan assists project
managers in keeping projects on schedule and within the resource budget.
Projects that involve geospatial data have unique QA and QC elements, which must be carefully considered
in the strategic planning process and subsequently incorporated into the QA project plan. Such projects
often use geographic information systems to retrieve, store, and process spatial, temporal, and related
environmental data to produce outputs used in decision making. The geospatial data unique to these
projects can be collected by direct measurements (e.g., by ground surveys or aerial photography) or
acquired from other organizations (e.g., U.S. Geological Survey maps and elevation data). This document
presents detailed guidance on how to develop a QA project plan for geospatial data projects. It discusses
how to implement the specifications set forth in Requirements for QA Project Plans for Environmental
Data Operations (EPA QA/R-5) for geospatial data, whether collected or acquired from other sources,
usually processed by geographic information systems.
Many of the requirements addressed in this document that are applicable to geospatial data project planning
and implementation were derived from the American National Standard "Specifications and Guidelines for
Quality Systems for Environmental Data Collection and Environmental Technology Programs"
(ANSI/ASQ, 1994), as cited in contract and assistance agreement regulations and incorporated in the
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revised EPA Order 5360.1 A (EPA 2000) and the QA manual 5360 A2 (EPA 2000). The scope of the
order's applicability includes "the use of environmental data collected for other purposes or from other
sources (also termed secondary data), including . . . [data] from computerized data bases and information
systems, [and] results from computerized or mathematical models." It is a frequent and often critical
component of this type of project. Implementation requirements include data processing to be performed in
accordance with approved instructions, methods, and procedures. Also required are evaluations of new or
revised hardware/software configurations and documentation of limitations on use of data.
Graded Approach
The EPA recognizes that the use of quality management components and tools in the Organization/Program
and the Project levels is based on a graded approach where components and tools are applied according to
the scope of the program and/or the intended use of the outputs from a process. This approach recognizes
that a "one size fits all" mentality to quality requirements is not appropriate for an organization as diverse
as the EPA.
EPA QA Requirements
The Agency-wide Quality System is a management system that provides the necessary elements to plan,
implement, document, and assess the effectiveness of QA and QC activities applied to environmental
programs conducted by or for the EPA. These directives, requirements and guidance documents may be
found at the EPA QA website: http://www.epa.gov/qualitv/.
The root QA document, from which other QA documents applicable to the collection and disposition of
GPS data are based, is the EPA Order 5360.1 (2000), Policy and Program Requirements for the
Mandatory Agency-wide Quality System, and the EPA Order 5360 (2000), Quality Manual for
Environmental Programs. These documents include coverage of environmental data,1 including any
measurements or information that describe location and information compiled from other sources such as
data bases (e.g., georeferenced data) or the literature (maps) under their requirements. Three of the
applicable requirements are:
• The use of a systematic planning approach to develop acceptance or performance criteria for all
work covered by the EPA Order. See Section 3.3.8 of the EPA Quality Manual for Environmental
Programs;
• The approval of Quality Assurance Project Plans (QAPPs), or equivalent documents defined by the
Quality Management Plan, for all applicable projects and tasks involving environmental data with
review and approval having been made by the EPA QA Manager (or authorized representative
defined in the Quality Management Plan); See Chapter 5 of the EPA Quality Manual for
Environmental Programs; and
• "Assessment of existing data, when used to support Agency decisions or other secondary purposes,
to verify that they are of sufficient quantity and adequate quality for their intended use."
1 environmental data - Any measurements or information that describe environmental processes,
location, or conditions, ecological or health effects and consequences; or the performance of
environmental technology. For the EPA, environmental data include information collected directly from
measurements, produced from models, and compiled from other sources such as data bases or the
literature.
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• "Requirements for QA Project Plans" are provided in Chapter 5 of the EPA QA Manual 5360 Al
(May 2000) for EPA personnel and "EPA Requirements for Quality Assurance Project Plans," EPA
QA/R-5 (EPA 2001) for extramural personnel.
Project Design Criteria
Systematic planning and the development of project and/or data quality objectives is required for all
projects. The EPA Guidance for the Data Quality Objectives Process EPA QA/G-4 and Guidance for
Choosing a Sampling Design for Environmental Data Collection Peer Review draft EPA QA/G-5S should
be referenced because the GPS locational data will probably be related to environmental media data in
analysis or data processing such as modeling.
In line with the EPA QA System is the EPA Locational Data Policy (LDP). The LDP is discussed in
Chapter 7 "Management of Locational Data" of this document. The LDP must be considered in project
planning with the EPA QA/G5 used as a blueprint (specifically QA Project Plan elements A5 and 7).
With regard to statistical analysis in project design, the EPA maintains a "graded approach." Refer to the
EPA Guidance for the Data Quality Objectives Process (G-4) EPA/600/R-96/055 for a full discussion of
this subject.
Quality Assurance Project Plans are reviewed and approved by EPA Project Managers with assistance and
approval of their EPA QA Managers. Technical and quality oversight is conducted as projects or their
tasks are implemented to determine whether they are conducted as planned, documented, and approved
(controls) or that timely corrective action is taken to assure that objectives are met (e.g., database files and
processed results such as hazard maps assessments). Note that a graded approach is used to tailor the QA
Project Plan to the project or task and if routine operations can be covered by a generic plan and associated
standard operating procedures.
Accuracy and Precision
GPS quality issues are predominantly related to identifying the accuracy of recorded data. In order to
ensure that collected data meets the needs of the project, guidelines must be used that maximize the
accuracy of the GPS unit. However, before specific guidelines are discussed, it would be instructive to
discuss accuracy and precision.
Accuracy is a measure of the amount of deviation of an observation, or a combination of a number of
observations, from the true value. Or, how close is the determined result from the known value (this is
called "bias"). Considering that the EPA's QA maintains a "graded approach," accuracy is presented as a
range value (i.e., plus or minus a value) that is determined by calculating the standard deviation or Root
Mean Square Error (RMSE) of the observations from the known value. For example, in a normal
distribution, a 68 percent confidence interval can be calculated by adding and subtracting one standard
deviation from the mean value and a 95 percent confidence interval by adding and subtracting two standard
deviations from the mean.
Precision means the closeness, tightness, or scatter of the positions of the points to each other. The second
standard deviation, which gives a 95 percent confidence interval, is expressed as "xx meters" from the
average value and is used to estimate the quality of code-based GPS points. Optimally, both good
accuracy and precision are desired with GPS points, with accuracy being preferred to precision. With
code-based GPS, precision is obtained. Depending on the GPS receiver type, it can use different signals
from the satellites. For example, Federal agencies have access to Precision Lightweight GPS Receivers
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(PLGR) which use the encrypted Y code. This improves the accuracy of these hand-held units particularly
where tree canopy or other signal interference is a problem. The reported accuracy of most commercial
units has not been clearly defined. There is not common agreement on whether the reported accuracy for a
unit represents one or two standard deviations. However, locational data is collected with Standard
Operating Procedures that specify exactly how the data is to be collected and processed and which have
proven to consistently provide accurate positions that make up the point. Then the precision of the data can
be used to estimate the quality of the point. If the data is properly collected and processed, the estimate of
the quality of the precision of the data can be used with confidence as the estimated accuracy of the data.
A graphic of precision and accuracy is shown below in Figure 6.
Precise and Accurate
Precise
Figure 6.
Accurate
Factors Affecting the Accuracy of the GPS Survey
There are many factors, which when present, have a certain affect on the accuracy of a location calculated
by a GPS receiver. Some of these factors are not always present, some cannot be avoided, and the effects
of some can be greatly reduced or eliminated. The following is a list of some of the more common
occurrences which can or will affect the accuracy of a GPS derived position and some of the ways in which
to reduce or eliminate their impacts.
Multipath
Multipath is the arrival of a satellite signal at the receiver along with one or more "reflections" of the same
signal which may have bounced off of an object or some atmospheric condition. A variety of factors
contribute to the impact of multipath on accuracy, such as the strength and the delay of the reflected signal
as compared to the true line-of-sight signal, the attenuation characteristics of the antenna, and the
sophistication of the receiver's measuring and processing techniques (Leick, 1995). Multipath effects can
introduce errors anywhere from < 1 meter to dozens of meters. Many multipath errors can be prevented by
planning a survey in order to avoid reflective surfaces such as buildings and large bodies of water and by
providing the GPS antenna with a clear view of the sky. The EPA QA Guidance Document G5g, Interim
Guidance for Geospatial Related Quality Assurance Project Plans, Sampling Process Design, Section Bl,
can be used to assist in developing a survey plan.
Atmospheric Delays
The density of the ionosphere affects the path of an electrical field such as a GPS signal. Changes in the
density of this layer of the Earth's atmosphere are caused by many factors, but they are primarily linked to
sunspot cycles. An increase in the activity of these cycles increases the density of the layer causing more
disturbances to GPS signals and reducing position accuracy Hittp://www.trimble.com/gps/1. Water vapor
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in the troposphere and atmospheric pressure may also have a slight affect on the accuracy of a GPS
position.
Baseline Length
The accuracy (actually the precision of positions related to each other, rather than the accuracy) of a
position will degrade as the distance increases between the base station receiver and the receiver at the
unknown location. For example, for the Trimble GeoExplorer II receiver, the estimate of this degradation
is 2 ppm or an accuracy degradation of 2 mm for every kilometer between the base and the rover. So, if a
GeoExplorer II, acting as the rover receiver, was collecting positions 200 km (124 mi) from the nearest
base station, then a degradation of 40 cm (15.7 in) may be expected in addition to the error values from
other sources. The older Trimble Pro XL unit also has a degradation of 2 ppm. The newer Trimble
ProXR unit has a degradation of 1 ppm. The best way to minimize this error is to use a base station
operating as close as possible to the survey site.
Position Dilution of Precision (PDOP)
This is a measure of the geometry of the satellite constellation which the GPS receiver is tracking. The
level of accuracy associated with positional measurements will vary depending upon the relative angles
between the range vectors of two or more satellites (GIS Technical Memo 3, 1992). The ideal situation is
to have a constellation of satellites which are spread evenly throughout the sky. The receiver automatically
tracks the satellites which will yield the best PDOP value. For example, if you are using a six-channel
receiver and there are eight available satellites above the horizon, the receiver will track only those four or
five satellites which will yield the best PDOP value, leaving one channel free to collect other information
such as the satellites' ephemerides. Satellites very low on the horizon adversely affect the accuracy of the
vertical component of the GPS position. This condition can be eliminated by setting a mask angle on the
GPS receiver so that it will disregard certain signals.
Signal-to-Noise Ratio (SNR)
This is a measure of the satellite signal strength in relation to background noise. Accuracy of the position
degrades as the strength of the signal decreases. One should refer to the GPS instrument manufacturer's
manual to find the range of the particular model's SNR. Subsequently, a determination should be made to
assess whether that SNR range is adequate for the purposes of the project or study. A SNR mask set at 8.0
(or higher, but not higher than 10.0) may reduce some multipath reflected signals since higher SNR's have
shown to provide better quality signals.
Data Quality Indicators and General Requirements
The following section describes data quality indicators used in GPS data collection and general
requirements for GPS use related to each indicator and based on the sources of inaccuracies mentioned
above.
Accuracy and Precision Requirements
As mentioned previously, the accuracy needed for a GPS survey is related to the goals of the project and
the type of information collected. Since the accuracies of GPS equipment and their procedures varies
greatly, different data collection procedures will be required for each purpose. In general, GPS data
collection can be divided into four main groups:
1. Gross position collection (13 meter horizontal accuracy) refers to the recreational grade GPS units.
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2. Coarse mapping grade collection (2-5 meter horizontal accuracy).
3. Fine mapping grade collection (1 meter horizontal).
4. Survey grade collection (1-2 cm horizontal and vertical accuracy).
The procedures of each of these will be treated separately within each data quality indicator section.
Multipath Avoidance Requirements
Multipath errors can be limited by using newer equipment, augmenting GPS work with laser range finders
to keep distance between the receiver and the source of the error, or by using conventional survey
techniques in areas of multipath. Many units manufactured after 1997 have software that significantly
reduces multipath; for example, Trimble's Everest multipath rejection software. GPS surveys in areas near
large reflective flat surfaces (such as buildings) without the benefit of lasers, conventional surveying, or
multipath cancelling software must be at a sufficient distance from the large reflective areas that the GPS
antenna sees the sky from 45 degrees and above.
Metadata File Collection Requirements
For gross data collection, no metadata is required to be collected since most recreational units do not have
the ability to record this information. The use of these recreational grade units would not be capable of
providing the essential method, accuracy, and description values that are required by the Locational Data
Policy. Therefore, their use should not be desired or encouraged, except where no other option exists for
collecting locational data. The standard metadata required by the Agency Locational Data Policy is
sufficient for other data collection efforts. For mapping grade and survey grade units, the following should
be saved to file:
1. Correction status,
2. GPS unit type,
3. PDOP, and
4. Standard deviation of points.
All of this data provides information on the overall quality of the GPS locations. The standard deviation
provides information on the precision of collected data. If the standard deviation is high, there is an
indication of possible interference. If the standard deviation of point data is greater than 10 times the
horizontal accuracy of the GPS unit, the data should be considered invalid.
Satellite Detection and Position Requirements
Due to the three-dimensional triangulation method used by all GPS units to determine location, a minimum
number of signals from at least four GPS satellites in the proper array in the sky are required for accuracy.
Unfortunately, most GPS units allow the user to utilize fewer satellites than the minimum, and in less than
ideal positions in the sky, than are required for quality data. Fortunately, GPS units also have the ability to
limit displaying and recording locational information until the proper number of satellite signals in the right
constellation is acquired by the unit. This function must be employed by USEPA users.
The utilization of four GPS satellites for 3-D positional fixes, with no significant precipitation, good
satellite visibility, a PDOP (indicator of a selected satellite geometric configuration) of no more than eight,
and simultaneous data recording of the base and remote units during the duration of the locational data
gathering effort, whether in real-time differential correction or postprocessing mode, is required for
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acceptable location results. For differentially corrected data, the datalogger must be set to read satellites at
no smaller than a 15-degree angle above the horizon.
Atmospheric and Ratio Requirements
Perhaps the easiest parameter to adhere to in GPS use is the requirement that no data is collected during
heavy precipitation. As far as any errors created by variations in the ionosphere, the gross and mapping
grade units have a fixed correction based on average ionosphere activity. The relative accuracies of these
units already reflect this limitation. The use of dual frequency receivers for survey grade GPS receivers
corrects atmospheric problems by utilizing the difference in real-time travel times of the two frequencies
caused by atmospheric variations.
Base Station Distance Requirements
For GPS projects requiring land-based differential correction, the error introduced by the distance from the
rover to the base unit, as measured by the manufacturer's specifications for the GPS unit and processing
software, should result in an error of no greater than 10 percent of the specified horizontal error of the unit.
This requirement applies predominantly to post processed data corrections. For real-time differential
correction, actual transmission distances will generally limit the error. For survey grade GPS work, the
distance from rover to base is limited by the radio transmission distance of approximately 10 km so no
requirements are necessary.
Calibration Requirements
Field calibration is not required for gross GPS work. The "graded approach" to QA is invoked for this
type of work.
GPS units, like any field electronic equipment, must be maintained in the proper working order to ensure
the highest quality data. A number of checks and procedures are required to ensure that the GPS unit is
working properly. These include checks of the software, wiring, and periodic checks against a known
location.
Ideally, for mapping grade data collection, if given sufficient notification, the user should acquire GPS
measurements at a nearby 1st order horizontal National Geodetic Survey (NGS) monument at the beginning
of each day of field work to ensure the overall performance of the unit matches its manufacturers stated
accuracy. In other words, the observed readings would be compared with the published coordinates of the
monument to give the user tangible assurance that the unit is performing within the manufacturer's
accuracy. However, this may not be feasible for most field work. Since using or finding NGS
monumentation is not always feasible, or possible, the accuracy of the survey will be based on the
manufacturer's specifications. Accuracy is determined by using differential corrections for locational data,
and by performing quality control checks on the locational data collected. The magnitude of the standard
deviation will provide an idea of the quality of the locational data, while the spatial distribution of the
individual positions inside a locational data file will provide visual clues for deleting obvious outliers. It is
recommended that each Region be allowed to decide what factors, if any, are used to determine the
accuracy of the points collected. Another field estimate of quality would be the comparison of two field
GPS units of the same type in the same location. The error should be no greater than that due to the unit's
specifications. For survey grade work, a first order benchmark (horizontal, vertical, or both depending on
the requirements of the work) is required. Therefore, no calibration is necessary.
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Completeness Requirements
Types of Samples Required: The types of samples that require GPS use should be determined in the
planning stage of data collection. It is not appropriate to require the highest accuracy to be attainable, nor
is it correct to say that every GPS survey demands an elaborate design. In some situations, such as in an
emergency response, a GPS survey crew may go from start to finish with no more of a plan than a minute-
to-minute decision can provide. Again, the graded approach must be applied with good judgement.
Data Collection Time and Frequency Requirements
Keeping the graded approach in mind, the time for residing at a particular location is dependent on the
accuracy required. If less accurate information is needed, then the unit can be operated in streaming mode
where the location is captured by the user based on the unit obtaining a stable result. Generally, this is
indicated by the unit and the time required at the location is minimal. If higher accuracy is required, then
the position to be captured should be occupied for a longer duration. Several results can then be captured
for the same location. These results can be improved by occupying the same location on different days and
different times of the day when the satellite configuration is different. Therefore, course mapping work
should require fewer positions for shorter duration than the fine mapping work.
The user must specify the requirements of the study in terms of Data Quality Objectives in the planning
phase and describe the operations to achieve the criteria in the Standard Operating Procedure. The
following examples show a hypothetical relationship, between different types of studies, and can be used
as "departure points" for establishing data collection time and frequency requirements for a project:
• For gross work with recreational units, a single position is acceptable. However, the use of these
units for Agency work is NOT encouraged.
• For coarse mapping work, a minimum of 12 positions is collected over a period of 1-3 minutes for
point data collection. The actual requirements should be described in the GPS Data Collection SOP
for the study, and any deviation from the SOP should be recorded.
• For fine mapping grade data collection, a minimum of 36 positions is collected over a period of 3-5
minutes. The actual requirements should be described in the GPS Data Collection SOP for the
study, and any deviation from the SOP should be recorded.
• For survey grade work, no averaging is required.
Data Evaluation
Once GPS data has been collected, depending on the survey goals, the data is evaluated for quality. For
gross data collection, recording information to satisfy the Locational Data Policy is sufficient. For
mapping grade data, the recorded standard deviation is an indication of the quality of the data and should
be used for screening purposes as mentioned. In addition, the recorded PDOP and correction status
provides additional quality checks. This raw information should be saved along with any pre-survey
calibration surveys with other project data in a database. Data of the locations can also be evaluated
against other available geospatial data such as digital orthophoto quads, topographic images, road and
parcel databases, etc. Any deviation from the SOP should be recorded.
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Section V
Core Elements of GPS Standard Operating Procedures
Planning and Preparation
Planning and Implementing a GPS Survey
The following sections will outline the basic steps involved in planning and conducting a GPS survey. In
order to complete a successful GPS survey, several steps must be taken prior to using the receiver in the
field. These steps will apply to the use of any of the various GPS receivers maintained by the Agency.
Most of the steps in the pre-survey and post-survey process will be conducted in conjunction with, or
entirely by, the GPS coordinator. Equipment will be on loan to those employees who have been trained on
the use of the GPS receiver. Those who require training or feel that retraining is necessary must notify the
GPS coordinator well in advance of a proposed GPS survey so arrangements can be made for training.
Training will be provided either on an as needed basis or through scheduled group training sessions.
It is extremely helpful if the field person who will be conducting the survey has some knowledge of the site
layout prior to data collection, either through published maps or previous site visits. This knowledge of the
survey site will help to expedite the survey by determining what features will be mapped and in what order.
Pre-survey Planning
• Contact the GPS Coordinator to identify the following prior to the GPS survey.
• The availability of the GPS equipment for the date(s) it is needed.
• List objectives of the survey.
• Make a determination as to what features will be mapped, sample point location identification, and
how they should be represented (points, lines, areas).
• Produce a checklist of each feature to be mapped so that none will be overlooked in the field.
• Site maps for determining in what sequence features will be mapped.
• Document the presence of any obstructions to satellite signals such as buildings or tree canopies
• Determine the necessity of a data dictionary (see below)
• Required accuracy of the survey (sub-meter, 5 meters)
• Extent and duration of the survey (how many features, how many days)
• Naming conventions for features and GPS file names
• Determine the need to use external sensors such as laser range finders, digital cameras, or depth
finders
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If an Agency regulated facility is to be mapped, a site description category should be used from the
latitude/longitude site description table from the Method, Accuracy, and Description (MAD) code tables
(see Table 1 for list of site descriptions). These site descriptions can be added to a data dictionary as
feature attributes and installed on a GPS receiver or data collector (see the section below for a description
of data dictionaries).
The answers to some of the above questions will determine what type of GPS receiver/data collector
combination will be required for the survey. Be mindful that a position represents only one part of a
feature.
The following section will outline which tasks will be completed by the GPS coordinator and the staff
person(s) requesting the GPS equipment for a survey.
Define Objectives of Survey
It is clearly important to initially establish the ultimate objectives of a GPS survey. Recognition of these
objectives early in the project planning process will help to focus the rest of the planning phase. The
accuracy requirements for the positional data needs to be defined, paying particular attention to the EPA
Locational Data Policy (See the Appendices section). From the discussion above, some distinct survey
objectives may include:
• Registration of remotely sensed photography or imagery,
• Evaluation of locational data quality of existing data, and
• Sample data collection following precise coordinates in a monitoring plan.
Define Project Area
This step is designed for establishing the overall project area and defining the limits of the survey. Maps
and/or aerial photos should be utilized extensively to familiarize the crew with the area prior to the actual
field work. For identifying the study area and surrounding environment, 7.5 minute topographic maps are
ideal. For locating particular sites by address a local street map will be required. A complete
understanding of the project area transportation network will also enable the field crew to maximize the
effectiveness of their field time. Much of this information is already available in digital form and can be
directly in conjunction with GPS site planning as well as validating the capture of the GPS locations.
Determine Observation Window and Schedule Operations
This involves determining the precise window of satellite availability and scheduling accordingly. With 26
satellites available for use, we generally are restricted for very short periods of time (usually less than 40
minutes in a continuous block of time and less than one hour during a 12-hour time period) during the day,
in open environments. However, in cities with many nearby tall buildings, GPS is often difficult to get.
Optimization of the schedule is dependent upon the size of the crew, the level of accuracy desired, the
logistics of setup, and the travel between control points. Many GPS units contain the satellite schedules in
their internal software. Updated satellite configuration and orbit information can be accessed via the
Internet.
A current satellite visibility almanac is invaluable in planning a survey mission. Provided by several
vendors, these almanacs provide information on the availability of satellite coverage. Since satellite orbits
are periodically adjusted, these almanacs require updating at least every month. Most vendors provide
updates using either electronic bulletin boards or regular mail. For final verification of availability, contact
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the U.S. Coast Guard GPS Users Service for information on the entire system or any individual satellites
that may be deactivated during your scheduled field work. Information is also broadcast by U.S. National
Institute of Standards and Technology (NIST) at 15 minutes past each hour
http://www.boulder.nist.gov/timefreq/stations/wwv.html.
QuickPlan from Trimble Navigation is an easy-to-use Windows-based software program which provides
information critical to the various components of planning a GPS survey: satellite availability, elevations,
azimuths, and Geometric Dilution of Precision (GDOP) calculations.
Several rules of thumb exist regarding available windows and angles above the horizon. Most almanac
software will yield good results for windows within one half degree of the survey station (approximately 30
miles). If your survey mission will span greater distances, then you may wish to iterate calculations for
several planned survey locations. For angles above the horizon, optimal results are achieved with satellites
25 degrees above the horizon; however, as little as 10 degrees works well in areas of minimal obstruction.
Be aware that this could present a problem if your going to differentially correct against a base station later
on, since the rover has to "see" the same satellites as the base.
Accuracy is heavily dependent upon the amount of observation time and number of observations taken at
each point. It is generally agreed that observation time can be reduced by increasing the quality of
observation time, i.e., observing a maximum number of satellites during 3-D viewing periods. Accuracy
can also be increased by repeated visits to the same location at different times.
Establish Control Configuration
For high accuracy work, known control points and/or benchmarks are located for both horizontal and
vertical control. This is usually accomplished by researching the records of various Federal, state, and
local agencies such as the National Geodetic Survey or the state geodetic survey. It is advisable to have,
where possible, at least two control points each for both vertical and horizontal positions so that there is a
double check for all control locations. NGS benchmark information can be obtained at
http://www.ngs.noaa.gov/.
It is of paramount importance that the reference datum within which the monument is located be defined.
The discussion provided later in this section will explain the reasons in detail. For horizontal coordinates,
the North American Datum of 1927 (NAD 27) or the newer Datum of 1983 (NAD 83) will be specified.
For vertical control coordinates, the National Geodetic Vertical Datum of 1929 (NGVD 29) or the new
North American Vertical Datum of 1988 (NAVD 88) will be referenced. If the NGS has redefined the
benchmark coordinates to correspond to the newer datums, coordinates will be available for both datums.
If the monument is located in a controlled-access setting, the appropriate individuals should be contacted to
obtain admittance. The station recovery section of monumentation data sheets provided by NGS describes
in detail how to locate a particular point and whom to contact for access.
Sensitivity to factors contributing to multipath is particularly important for positioning a receiver station
and antenna. In particular, control points/areas should not be near power lines, substations, or large metal
objects which can cause multipath interference and corrupted data. Since observation of these proximate
features may not be possible until the survey reconnaissance is performed, having backup sites ready will
save time.
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Choosing control points for use as base stations may require a physical inspection of the site. Ideal
locations will have a near 100 percent clear view of the sky and be easily accessible. They should also be
located in areas of low vehicular and pedestrian traffic. Where real-time kinematic surveys or post
processing are being planned, government agencies or other organizations may already have established
base stations in the area. They should be contacted to ensure that the base station is recording at the
planned time of the survey. In many areas, vendors and other organizations have operating base stations
that have web access for use in post processing.
Select Survey Locations
Obtain a list of the facilities or features targeted for data collection. A good suggestion is to organize the
site lists alphabetically by city and alphabetically by street name within each city. This will facilitate initial
route planning to visit each and serve as a master list. If possible, plot the general location on a field map
and highlight a local street map to serve as a general navigation aid. Similarly, plot potential base stations
to serve as control points on a 7.5-minute topographic map and local street map.
If the survey point to be obtained is located on private property, care should be taken to pursue appropriate
notification and access protocol. This includes preparation of a letter of introduction and formal contact
with the property owner/manager. A sample letter is included in the Appendices section.
The points/areas should have continuous and direct line-of-site to the path of the satellites in the sky.
Based on the view provided by satellite window planning software such as QuickPlan, and the survey
team's knowledge of the natural and man-made topographic features, it may be possible to predict masking.
As with control points, obstructions and other factors can cause interference and corrupted data during the
survey. It is advisable to note any adverse conditions on a form when collecting data. This will be helpful
in the postprocessing phase.
If point data being collected is to be used as control for photogrammetric operations, then the point
locations must be photo identifiable on the imagery to be used for photo registration. If the registration is
to be used with historic imagery, the locations should be landmarks present and identifiable for the entire
period of history to be reviewed. Such landmarks might be corners of the street network that have
remained constant, street/railroad intersections, hydrants, or other public works.
Equipment Logistics
Survey planning action items in this area include: determination of equipment availability (laptop PC, GPS
units, transport vehicle, monumentation equipment), and checking equipment for necessary repair and
maintenance (batteries charged in PC and GPS unit, PC disk loaded with necessary software and has
available disk space).
This is the time to collect and pack field survey equipment. In addition to the above items, experienced
crews carry everything from a compass and tape measure to manuals and almanac printouts. Suggested
checklists are provided in the Appendices section.
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Reconnaissance
The purpose of this phase is to:
Locate and Verify Control Point Locations
For high accuracy work, this is critical to the success of the overall survey. Often, monuments have been
damaged, stolen, buried or vandalized. If a control point cannot be recovered, a replacement must be
located. This can drastically change the schedule and logistics of the field survey. Also, it may be found
that a monument's location has shifted somewhat.
Plan to visit each of the control points at least twice during the survey. Collecting redundant data is useful
in determining the quality and accuracy of the overall survey. The duration of each fix should be
approximately 3-5 minutes, but it may be adjusted depending on data accuracy needs as articulated by the
EPA's QA graded approach.
Preview Instrument Locations
Obtain permissions and verify accessibility. It will often be necessary to coordinate activities with property
owners, local law enforcement, and/or land management officials in order to ensure safe and authorized
access to the instrument locations. Verify that there are not any visible multipath-contributing or masking
features. Identify any natural or man-made obstacles to direct access of the survey point.
Physically Establish Point Locations
This is accomplished by using a standard surveying marker such as an iron pipe, a hub and tack, or a brass
nail. All points should be documented with detailed descriptions in a log book (refer to Appendix F for a
sample form). If nearby multipath or masking features are unavoidable, note their presence. It may be
necessary to physically offset the GPS control point from an obstructed benchmark. This can effectively be
accomplished using a compass and tape measure. Whatever approach that is used, the end-use of the
project data should drive the establishment of reproducible marking.
Survey Execution
The actual GPS survey consists of:
Establishing a Schedule of Operations
This involves determining the window of satellite configuration availability and scheduling the GPS
sessions. This is dependent on the size of the crew, the level of accuracy desired, and the logistics of setup
and travel between control points. Maximum data quality and collection efficiency can be obtained by
arranging data collection periods to coincide with periods of 3-D or better satellite visibility.
Pre-survey: The Day Before
Plan on arriving the day before. Charge all batteries. Many GPS collection systems utilize a battery
system which requires either 8-hour or overnight charging. Review the travel routes to survey sites and
base stations, if required, and coordinate with local personnel. Review use of unfamiliar equipment and
understanding of procedures.
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Pre-data Collection: Establishing a Base Station
The type of survey will dictate if a base control station in the field is required. If required and the location
is not secure or if the data collection period is particularly long, part of the survey crew may be required to
remain at the site. Logistical considerations will need to be scheduled, i.e., shut down periods for
downloading files, changing battery packs, and when to terminate collection. Once a setup at a base station
begins, the GPS units will need to be initialized. Depending upon the location and familiarity with
equipment, this activity can take anywhere from a few minutes to a couple of hours.
Field collection data should be saved as digital files in order to facilitate depositing the data into
Information Management Systems.
Data Collection: Performing the GPS Survey
The crew must warm up, check and program the receiver for proper operation. Most vendors currently
recommend collecting fixes for discrete point data for a period of 3-5 minutes, at a 1- or 2-second interval.
Many software packages require approximately 35-40 readings per point to perform statistical analyses.
Any deviation from this would be reflected in each Region's SOP.
Depending on the unit being utilized, sufficient battery power must be available. For high accuracy work,
the receiving antenna must be leveled on a tripod and centered exactly over the control point location. Log
sheets containing critical information on position, weather, timing, height of instrument, and local
coordinates must be maintained. Once the session is completed, the receiving equipment must be
disassembled, stored, and log and tape files documented.
If the survey to be performed will span over numerous days, it is likely that the data will be transferred
from the GPS to a lap top PC with some regularity. Data from the base station as well as the roving unit
will need to be collected with equal frequency.
Returning from the Field
This is the time to perform other post-survey tasks. Before leaving the site, document any unique
problems. After returning from the field, complete other housekeeping chores such as recharging the
system and cleaning the equipment. Use checklists to make sure equipment is in working order and any
consumable supplies are reordered. Post processing may be conducted after returning from the field.
Tools for post processing are more easily used and controlled in an office environment. The common steps
in post processing are transferring the data from the field to the lab, conducting the initial stages of
processing, computation of the solutions for critical factors, data conversion for use in a GIS, and the final
documentation and reporting. Each of these stages is discussed in detail below.
Data Transfer
There are currently two common methods of collecting data in the field; using a GPS unit with a datalogger
or using a GPS unit with a laptop/notebook computer. With the latter method some users subsequently
perform all processing directly on the same device. More commonly, data is transferred into a computer.
This consists of reading the raw data from the GPS unit into a structured data base for processing. As with
any computer data, backup copies should be made immediately.
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Initial Processing
The electronic GPS data stream may not be immediately useable. It normally consists of satellite
navigation messages, phase measurements, user input field data and other information that must be
transferred to various files for processing before computations can be accomplished. Depending upon the
hardware and software vendor, many of these operations are transparent to the user. There are five
components to the initial processing phase performed by GPS "firmware," software that comes with the
GPS units:
1. Orbit Determination: Using satellite navigation messages, one unambiguous orbit for each satellite is
computed,
2. Single-Point Positioning: Clock corrections and parameters for each receiver are computed,
3. Baseline Definition: General locations of receiving stations are established, computing the best pairs
of sites for baseline definition,
4. Single Difference File Creation: The differences between simultaneous phase measurements and the
same satellite from two sites. This is the basic data from which network and coordinate data will be
derived, and
5. Data Screening and Editing: Automatic and manual screening of the single difference files and
editing of data obviously affected by breaks, cycle slips, or multipath.
In some instances, depending on the type of maintenance and upgrades that are going on to the NAVSTAR
constellation at the time of the survey, utilization of the actual ephemeris rather than the ephemeris
projected prior to the survey date may improve solution accuracy. Actual ephemerides are available 2
weeks after a given survey date.
In the data screening and editing step above, there are at least three considerations that might be taken in
editing. Outlier position data can be removed from a data file. This editing should be guided by
establishing an absolute deviation threshold, using the mean coordinate as a reference. The threshold
criteria might be varied to determine the sensitivity of the solutions to this editing. Data points collected
immediately after a break in the data stream, such as in the event of masking, should be edited out because
these positions will be less reliable.
Computation
This component uses the preprocessed data to compute the network of sites and give a full solution showing
geographical coordinates (latitude, longitude and ellipsoidal height), distances of the vectors between each
pair of sites in the network, and several assessments of accuracy of the various transformations and
residuals of critical computations. If the standard deviation for a differential mode position is greater than
5 meters, removal of outlier coordinates and recalculation of a position mean is advised (Lange, 1990).
This should be left up to the Regions, since better quality (i.e., +/- 1 meter data) might be desired, or lower
quality data may suffice. Also, samples taken while on an unanchored boat or from a helicopter would
require individual attention.
Data Conversion to GIS
Data conversion is accomplished by use of Data Export Utilities obtainable from the GPS manufacturer.
These utilities should accompany the Data Processing Software packaged with the GPS Equipment.
Example formats are: Arc View, Arclnfo, dBase, ASCII, Maplnfo, AutoCAD, etc. Before exporting,
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ensure that the correct coordinate system and datums are chosen. Contact the regional GIS coordinator on
the required system for use with GIS layers.
Documentation and Reporting
The documentation and reporting requirements for spatial data include both the EPA Locational Data
Policy and the Federal Geographic Data Committee's Metadata Standard, an Executive Order.
Information on both the standards and assistance with the reporting requirements can be obtained from the
EPA Locational Data Improvement Project.
EPA established a Locational Data Policy (OIRM Policy 2100, 8 April 1991) to standardize principles for
collecting and documenting latitude and longitude coordinates and associated attributes for facilities, sites,
and monitoring and observation points regulated or tracked under Federal environmental programs within
the jurisdiction of the Agency (ref Chap. 13 IRM Policy Manual - Locational Data). This policy applies
to all Agency divisions and personnel of agents, contractors and grantees of the Agency who will, in
essence, be collecting, compiling and maintaining spatial data sets for environmental program support. It
states that the collection of coordinates using latitude/longitude has become the preferred coordinate system
for identifying features and that the use of the GPS is the preferred method for obtaining these coordinates.
The Locational Data Policy has also established an Agency-wide accuracy goal of+/- 25 meters. The LDP
+/- 25 meter accuracy goal was written as a goal and not a standard because the achievement of a certain
accuracy is based primarily upon the best available data collection technology. The current best available
technology, GPS, allows for the acquisition of data with a < 10-meter accuracy and has been embraced by
the Locational Accuracy Task Force (LATF) as the coordinate data collection technology of choice.
One of the more important aspects of the Policy is the documentation requirement. The Method, Accuracy,
and Description (MAD) codes need to accompany the facility-based spatial data sets. The MAD code
fields listed below are outlined in the Method, Accuracy, and Description (MAD) codes v 6.1. The
document represents a procedure for standardizing the coding of geographic information and associated
attributes for use in a geographic information system (GIS) or other statistical software program. It
requires that all geographic coordinates acquired by Agency employees, contractors and grantees be
accompanied by certain specific information. See the EPA Locational Data Policy section in the
Appendices.
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Section VI
Management of Locational Data
The power of place has demonstrated exceptional potential to serve the Agency in addressing its mission
and business needs. The ability for programs, regions and the public to easily access, analyze, and use
geospatial information is recognized as a key component of environmental management. The EPA has
placed a heightened emphasis on mapping and integrating data across programs to support environmental
protection. As programs increasingly rely on mapped data to guide environmental protection activities, the
EPA needs to ensure that locational data is of sufficient quality for intended uses. Data mapping and
integration is hampered by locational information that is nonexistent, inaccurate, or of unknown quality.
This valuable data is fragmented across many organizational entities, systems and platforms, which makes
access difficult.
To improve the Agency's locational data for facilities and other environmental features, the EPA launched
the Locational Data Improvement Project (LDIP) in 1996. The goal of this project was to populate the
Envirofacts database and other repositories of spatial information with locational information (e.g., latitude
and longitude records) of documented origin, for all data subject to the EPA's Locational Data Policy,
including regulated facilities and sites, operable units, and environmental monitoring and observation
locations. A secondary objective is to support the infrastructure needed to manage these data in a manner
that yields integration across national, regional, tribal, and state systems. The intent is to support the
EPA's movement toward data integration based on location, thereby promoting the use of the EPA's data
resources for a wide array of cross-media analysis, such as community-based ecosystem management and
environmental justice.
The launching of the EPA's Office of Environmental Information (OEI) in October 1999 resulted in more
foci on LDIP to help ensure the acquisition, documentation, storage, and use of locational data to help meet
the geospatial needs of the Agency. Critical LDIP activities include maintaining locational information in
the Envirofacts Warehouse, improving facility identification through geocoding (i.e., calculating a
coordinate value for an entity based on the reported full location address for that entity), supporting the
Facility Linkage Application (FLA), and providing the Geographic Information System (GIS) community
in program system offices with access to locational data.
Another important aspect of LDIP is the requirement that all locational information in Envirofacts retain
Method, Accuracy, and Description (MAD) codes. These codes, which conform to the Locational Data
Standard, describe every aspect of the collection of that particular location. For locational data that resided
in the programmatic databases prior to LDIP, it was difficult to know the quality of a particular coordinate,
how accurate it was, and what it actually represented because method, accuracy, and description
information was, for the most part, not available.
The locational information in Envirofacts is stored in the Locational Reference Tables (LRT). The LRT
act as a storehouse for the actual locational data and business rules that are applied to them in order to
provide the most accurate information available for depicting the locations of federally regulated entities.
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Although LDIP has improved the EPA's locational data, there have also been a number of challenges.
Regions, states and programs have been working to improve data coordinates but in a rather uncoordinated
fashion with very limited and unsustained resources. Some of the challenges are: lack of communication
and of coordination between interested parties, duplication of efforts between regions and programs in
obtaining resources and performing activities to acquire better locational data, lack of understanding of
what might be the "best" locational coordinates, and absence of leadership to centralize efforts to prioritize
environmental sites for improvement. To address these and other concerns of locational data, the
Locational Data Improvement Subcommittee (LDIS) was established in March 2001. The vision of the
LDIS, as stated in its Action Plan, is to ensure that locational data is collected and documented as an
integral part of the Agency's regional and program business. One of the key goals of this vision as it
relates to this guidance is that Global Positioning System (GPS) and related technologies are well
supported and used within the programs, regions, states, and tribes to collect, document, and quality check
locational data.
The Value of Documenting Locational Data: One of the challenges when doing an environmental
assessment or analysis is finding documentation about data, commonly called metadata. Documentation
provides secondary data users with information about data sets that will help users understand the data and
can be used to evaluate the data set's appropriateness for a specific project. A well-documented data set
will increase the confidence in the conclusions made after using the data. In summary, documenting data
facilitates data sharing and reuse. Complete documentation includes information about:
1. Content
2. Quality
3. Accuracy
4. Methods
5. Intended use
6. Lineage (source information)
7. Availability
8. Distribution and Access
9. Contact
Documentation involving methods, accuracy, and content are significant metadata entities for geospatial
data. Geospatial metadata that describes the data collected by GPS can have information about the quality
of the positional accuracy for horizontal and vertical coordinates. This information is useful when
determining the data's fitness for use. Contact information can also be a source for providing further data
set clarification if it is needed. One of the impediments of merging data layers when conducting an
environmental assessment is the confusion over the data element names and definitions in each layer. Full
documentation will clarify this ambiguity enabling integration and analysis of data layers to occur.
The Agency has a suite of metadata tools for documenting data that are available to everyone in the
Agency, states, regions, and the public via the Internet. For documenting a data set, users can enter
information into the Environmental Information Management System (EIMS). For documenting the
individual data elements, users can enter information into the Environmental Data Registry (EDR). These
two cataloging systems will be integrated in the near future. EIMS is an online metadata repository with
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links to data files and databases. There are built in quality assurance controls within EIMS, including the
review of metadata content by a metadata librarian. EIMS supports the Dublin Core and the complex
Federal Geographic Data Committee documentation Standards for digital geospatial metadata and supports
Executive Order 12906 serving as the EPA's Clearinghouse for Geospatial data on the National Spatial
Data Infrastructure (NSDI).
To learn more about EIMS visit http://www.epa.gov/eims or call the EIMS Support Center at
800-334-2405. To learn more about EDR visit http://www.epa.gov/edr.
Relationship of LDIS Action Plan Efforts and GPS-Technology Implementation Guidance (TIG)
Development Effort: It is important that there is strong collaboration between the efforts of the GPS-TIG
development and LDIS Action Plan. The Agency has advocated an Agency-wide accuracy goal of +/- 25
meters. For lat/long data points to be of any credible value, this stated accuracy goal must be met. GPS is
the current available best technology for the acquisition of data with a < 10-meter accuracy and has been
embraced by the Locational Accuracy Task Force (LATF) as the coordinate data collection technology of
choice. Therefore, the work of the LDIS Action Plan and the GPS-TIG would be served by coordinating
and closely aligning the efforts. Revising the Locational Data Policy has been identified as an action item
in the LDIS Action Plan and will be the area that addresses the use of the GPS-TIG.
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Section VII
Legal Considerations
Certain types of locational data can present legal issues relating to the collection, storage, maintenance and
dissemination of the information. If the data is sensitive, due to privacy concerns, confidential business
concerns, or post-September 11 security issues, the Agency may need to limit dissemination of the data, or
release it only in masked or aggregated form. The Agency discloses data generally for three reasons:
because a statute requires the disclosure, because the data has been requested under the Freedom of
Information Act, or because the Agency has decided that it is in the public interest to make the information
available on its own initiative. With expanding use of computers and the Internet, publishing data on web
sites has become a common means of making information widely available. With the increase of
information available to the public, it has resulted in a heightened concern about potential misuse of
sensitive data.
Collection of Data
Agencies may not collect information from 10 or more persons by means of identical questions, or identical
reporting or record-keeping requirements, unless the collection is cleared by the Office of Management and
Budget (OMB). This is required by the Paperwork Reduction Act, 44 U.S.C. § 3501 et seq. If
information is requested from 10 or more persons by means of identical questions, the Agency must obtain
a control number from OMB and display the control number in accordance with OMB regulatory
requirements. If there are any questions whether the Paperwork Reduction Act applies to a collection of
information, Agency legal counsel should be consulted.
Storage and Maintenance of Data
The Federal Records Act (FRA), 44 U.S.C. § 3101 et seq., and § 3301 et seq. The FRA requires agencies
to maintain and dispose of official records in accordance with formally adopted records retention schedules.
Official records include material that is required by law to be developed or that documents EPA actions or
the formulation of EPA policies or decisions. Data files and raw data may be official records for purposes
of the FRA if the data is necessary to document the decision trail of the Agency's action. The records
retention schedules and other information about the FRA may be found at http://www.epa.gov/records.
Release of Data Pursuant to Freedom of Information Act Requests
The Freedom of Information Act (FOIA), 5 U.S.C. § 552, provides that agencies will make records
available to the public upon written request, unless one of nine specific exemptions apply. The Electronic
FOIA amendments of 1996, Pub. L. No. 104-231 require agencies to provide records in electronic format if
requested, and if reasonably possible. Agencies must also develop electronic reading rooms and make
agency-created documents that have been requested and released available electronically if the agency
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decides they will be subject to subsequent requests. It is important to note that, for the purposes of
responding to FOIA requests, agency "records" are not necessarily limited to agency "records" as defined
under the FRA. Responsive records for FOIA purposes include all non-personal documents in existence at
the time of the FOIA request that are in the agency's possession. Once records have been identified as
responsive to an FOIA request, they must be retained pursuant to the FOIA records retention schedule even
if they otherwise would not be agency records under the FRA.
EPA FOIA regulations are found at 40 C.F.R. Part 2; the Department of Justice FOIA Guide may be
accessed on the Internet at http://www.usdoj.gov/oip/foi-act.htm.
Privacy Concerns
The Privacy Act, 5 U.S.C. § 552a, covers systems of records from which information is retrieved by an
individual's personal identifier, such as name or Social Security Number. Most Agency records are not
maintained in Privacy Act systems. However, many agency records may contain information that is
personal to an individual, and if the personal privacy interest of the individual outweighs the public's
interest in the information, the information is withheld from disclosure pursuant to Exemption 6 of the
FOIA.
In addition, there are prohibitions on the use of information generated from research on human subjects.
See, for example, 28 C.F.R. Part 46, Protection of Human Subjects; 28 C.F.R. Part 22, Confidentiality of
Identifiable Research and Statistical Information.
A-110
In 1997, the EPA refused to obtain data from the Harvard School of Public Health that had been used in
EPA grant-funded studies. Due in large part to adverse reaction to this situation, Congress directed OMB
to revise OMB Circular A-l 10 to "require Federal awarding agencies to ensure that all data produced
under an award will be made available to the public (pursuant to FOIA)." The Supreme Court had
previously ruled that records in the possession of a Federal grantee but not in the Agency's possession were
not considered "agency records" and therefore not subject to the FOIA. Agencies previously had no
obligation to obtain records from grantees.
OMB published its final revision to Circular A-l 10 on October 8, 1999 (64 Fed. Reg. 54926), and the
EPA adopted the amendment March 16, 2000 (65 Fed Reg. 14407, 14417). Under new 40 C.F.R.
§30.36(d), in response to an FOIA request, the EPA must request from its recipients, and the recipients
must provide, "research data relating to published research findings produced under an award that were
used by the EPA in developing an agency action that has the force and effect of law." The term
"published" is defined as either when the findings are published in a peer-reviewed scientific or technical
journal or when a Federal agency publicly and officially cites the findings in support of agency action that
has "the force and effect of law."
The revised regulation also narrows the definition of "research data" to exclude preliminary analyses,
drafts of scientific papers, plans for future research, peer reviews, communications with colleagues, and
physical objects. It also excludes confidential business information, personal privacy material, and similar
information protected by exemptions under FOIA.
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Data as Confidential Business Information
Locational data, or secondary data, may be claimed by a company to be confidential business information,
commonly referred to as "CBI." EPA regulations governing the determination of CBI claims are found at
40 C.F.R. Part 2, Subpart B.
Toxics Release Inventory (TRI)
The TRI is a publicly available, searchable database that includes information on over 20,000 facilities and
the releases and transfers of toxic chemicals at or from those facilities. The TRI was developed under the
Emergency Planning and Community Right-to-Know Act (EPCRA) and the Pollution Prevention Act
(PPA), and it is required by statute to be made publicly available by computer telecommunications and
other means. Currently, the main methods of accessing the data are the Internet and the EPA Public Data
Release, which is a report that compiles much of the data on a yearly basis. The EPA currently collects
facility identification information, including facility name, street, city, county, state, zip, mailing address (if
different), latitude and longitude, Dun and Bradstreet number, EPA ID Number (RCRA ID number),
NPDES Permit numbers, and Underground Injection Well Code ID numbers. In addition, the EPA
currently collects the name of the facility's parent company, if applicable, and the parent company's Dun
and Bradstreet number. All of this data is currently publicly available.
Locational Data as Intellectual Property
Under the Copyright Act, 17 U.S.C. § 101 et. seq., data itself is not generally subject to copyright
protection. However, information about data, or software programs, may be copyrighted. Licensing
agreements are common in the software industry. Since these are contracts binding the Agency, they must
be reviewed by Agency legal counsel to ensure compliance with Federal law. If there are questions about
the ability to release or disseminate secondary data that is copyrighted, Agency legal counsel should also be
consulted.
This section only presents a summary of the main issues raised. For further information, or if you have
questions about the legal issues, please contact Agency legal counsel.
32
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Section VIM
References
Ackroyd, Neil, and Robert Lorimer. Global Navigation: A GPS User's Guide. Lloyd's of London Pr Ltd.,
1990.
Aronoff, S. Geographic Information Systems: A Management Perspective, WDL Publications, Ottawa
Canada, 1995.
Bodnar, Captain A. Nicholas. National Geodetic Reference System Statewide Upgrade Policy. National
Geodetic Survey, June 1990.
Corn, David. Surveying By Satellite. Catalyst, February 1990, pp. 43-44.
Denaro, R. P. and R. Kalafus. Advances and Test Results in Differential GPS Navigation. The Journal of
Navigation, vol. 43:1, pp. 32-40, 1990.
Dewhurst, W. T. Shift-On-A-Disk. Converting Coordinate Data from NAD 27 to NAD 83. ACSM
Bulletin, No. 126, 1990, pp. 29-33.
Hartl, P. H. Remote Sensing and Satellite Navigation: Complementary Tools of Space Technology.
Photogrammetric Record, vol. 13:74, pp. 263-275, 1989.
Giles, John, Bob Greenlaw, and Charles Wordell. "Maine City Quickly Improves Infrastructure
Management." ArcUser: The Magazine for ESRI Software Users. July-Sept. 2000: 28-29.
Hum, J. GPS, A Guide to the Next Utility. Trimble Navigation Ltd., Sunnyvale, California, 1989, 76 pp.
Kruczynski, L. R. and A. F. Lange. Geographic Information Systems and the GPS Pathfinder System:
Differential Accuracy of Point Location Data. Trimble Navigation, Limited study report, 1990.
Kruczynski, L. R. Differential GPS: A Review of the Concept and How To Make It Work. Trimble
Navigation, Limited study report, 1990.
Kruczynski, L. R., W. W. Porter, D. G. Abby, and E. T. Weston. Global Positioning System Differential
Navigation Test at the Yuma Proving Ground. The Institute of Navigation, 1986.
Lang, Laura. Managing Natural Resources with GIS. Redlands: ESRI, Inc., 1998.
Lange, A. F. and L. R. Kruczynski. Global Positioning System Applications to Geographic Information
Systems. Proceedings from the Ninth Annual ESRI ARC/INFO User Conference, Palm Springs,
California, 1989. 4 pp.
33
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Langely, R. B. Innovation Column: Why is the GPS Signal So Complex? GPS World, Vol. 1:3, pp. 56-
59, 1990.
Locational Data Policy Implementation Guidance (LDPIG). U.S. EPA Office of Information Management
Resources, Washington, B.C., 1991.
McDonald, K. D. GPS Progress and Issues. GPS World, Vol. 1:1, p. 16, 1990.
McDonald, K. D., E. Burkholder, B. Parkinson, J. Sennott. GPS for the Environmental Protection Agency,
Course 355. Navtech Seminars, Inc., November 1991.
National Geodetic Survey. National Geodetic Reference System Statewide Upgrade Policy. 1990.
Puterski, R. GPS Applications in Urban Areas. Proceedings from the Tenth Annual ESRI ARC/INFO
User Conference, Palm Springs, California, Vol. 1, 1990, 12 pp.
Slonecker, E. T. and J. A. Carter. GIS Applications of Global Positioning System Technology. GPS
World, Vol. 1:3, pp. 50-55, 1990.
U.S. Department of Defense/Department of Transportation, 1984. Federal Radionavigation Plan. Final
Report: March 1982-December 1984. U.S. Department of Defense Document #DOD-4650.4 and
U.S. Department of Transportation document #DOT-TSC-RSPA-84-8.
Wells, D., N. Beck, D. Delikaraoglou, A. Kleusberg, E. J. Krakiwsky, G. Lachapelle, R. B. Langley, M.
Nakiboglu, K-P Schwarz, J. M. Tranquilla, and P. Vanicek. Guide to GPS Positioning. Canadian
GPS Associates. Fredericton, New Brunswick, Canada. 1988.
Hum, Jeff. (1989). GPS, A Guide to the Next Utility. Trimble Navigation Limited.
Leick, Alfred. (1995). GPS Satellite Surveying, 2nd Edition. New York: John Wiley & Sons.
Trimble Navigation Limited. (1997). A New Level of Accuracy for Differential GPS Mapping
Applications Using EVERESTJ Multipath Rejection Technology. Mapping and GIS Systems
Division. Document #102. pp. 1 -7.
Trimble Navigation Limited - Operations Manuals for the following GPS Receivers: GeoExplorer II
(1996) P/N 28801-00. Revision B. Version 2.11; Pathfinder Basic (1990) P/N 16848. Revision B.
Release 1.00; Pathfinder Professional (1990) P/N 16177. Revision G. Release 1.42; Pathfinder
Pro-XL (1996) P/N 28380-00. Revision B. Version 3.00; TDC2 Asset Surveyor Software Users
Guide (1996) P/N 31175-00. Version: 3.10.
Trimble Navigation Limited. (1996). Mapping Systems (Figures). General Reference. P/N 24177.
Revision B.
U.S. Environmental Protection Agency. (1992). GIS Technical Memorandum 3. Global Positioning
Systems - Technology and Its Application in Environmental Programs, Research and Development
(PM-225). EPA/600/R-92/036.
34
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U.S. Environmental Protection Agency. (2001). EPA QA Guidance for Developing Geospatially-related
Quality Assurance Projects, EPA/600/R-01/062.
U.S. Environmental Protection Agency. (1996). Locational Data Improvement Project Plan, Office of
Information Resources Management, Contract Number 68-WI-0055. Delivery Order Number 065,
Prepared by: EPA Systems Development Center. SDC-0055-065-JB-5057A.
U.S. Environmental Protection Agency. (1991). Locational Data Policy, Chapter 13, Office of
Information Resources Management.
U.S. Environmental Protection Agency. (1994). Method Accuracy Description (MAD) v. 6.1.
Information Coding Standards for the U.S. EPA's Locational Data Policy. Prepared by the Locational
Data Policy Sub-Work Group of the Regional GIS Work Group.
Van Sickle, J., GPS for Land Surveyors, Ann Arbor Press, Second Edition, 2001.
35
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Appendix A
Glossary of GPS Terms
Almanac: Information describing the orbit of each GPS satellite, including clock corrections and
atmospheric delay parameters. An almanac is used by a GPS receiver to facilitate rapid satellite signal
acquisition and is also required by Trimble's Mission Planning Software.
Baseline: Consists of a pair of stations for which simultaneous GPS data has been collected.
Cadastral Survey: Survey performed to establish legal and political boundaries, typically for land
ownership and taxation purposes.
Channel: A channel of a GPS receiver consists of the radio frequency, circuitry, and software necessary to
tune the signal from a signal GPS satellite.
Control Segment: A worldwide network of GPS monitoring and control stations that ensure the accuracy
of satellite positions and their clocks.
Cycle Slip: A discontinuity of an integer number of cycles in the measured carrier beat phase resulting
from a temporary loss-of-lock in the carrier tracking loop of a GPS receiver.
Dilution of Precision: The multiplicative factor that modifies range error. It is caused solely by the
geometry between the user and his or her set of satellites; known as DOP or GDOP.
Ephemeris: The predictions of current satellite position that are transmitted to the user in the data message.
Federal Radionavigation Plan (FRP): Congressionally mandated, joint DOD and Department of
Transportation (DOT) effort to reduce the proliferation and overlap of federally funded radionavigation
systems. The FRP is designed to delineate policies and plans for U.S. government-provided
radionavigation services.
Geodetic Surveys: Global surveys done to establish control networks (consisting of reference or control
points) as a basis for accurate land mapping.
Geometric Dilution of Precision (GDOP): See Dilution of Precision.
Ionosphere: The band of charged particles 80 - 120 miles above the Earth's surface.
Mask Angle: The minimum acceptable satellite elevation above the horizon to avoid blockages of line-of-
sight.
36
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Multipath Error: Errors caused by the interference of a signal that has reached the receiver antenna by two
or more different paths. This is usually caused by one path being bounced or reflected.
North American Datum of 1927 (NAD 27): Older and obsolete horizontal datum of North America. NAD
27 depends upon an early approximation of the shape of the Earth, known as the Clarke Spheroid of
1866, designed to fit only the shape of the conterminous United States, and utilizing a specific Earth
surface coordinate pair as its center of reference.
North American Datum of 1983 (NAD 83): Official horizontal datum of North America. NAD 83 relies
on the more precise Geodetic Reference System of 1980 (GRS 80), employs a geocentric ellipsoid
model, and utilizes the Earth's center of mass as its center of reference.
North American Vertical Datum of 1988 (NAVD 88): Effort underway by NGS to readjust the North
American Vertical datum. The NAVD 88 readjustment will remove distortions from the continent-
wide vertical geodetic (height) reference system.
Point Positioning: Positioning mode in which a position is identified with respect to a well-defined
coordinate system, commonly a geocentric system (i.e., a system whose point of origin coincides with
the center of mass of the Earth).
Positional Dilution of Precision (PDOP): Measure of the geometrical strength of the GPS satellite
configuration.
Pseudo-Random Noise (PRN) Code: A signal with random noise-like properties. It is a very complicated
but repeated pattern of 1's and O's.
Pseudo-Range: A distance measurement based on the correlation of a satellite-transmitted code and the
local receiver's reference code that has not been corrected for errors in synchronization between the
transmitter's clock and the receiver's clock.
Satellite Configuration: The state of the satellite constellation at a specific time, relative to a specific user
or set of users.
Satellite Constellation: The arrangement in space of a set of satellites.
Selective Availability (S/A): Intentional degradation of the performance capabilities of the NAVSTAR
satellite system for civilian users by the U.S. military, accomplished by artificially creating a
significant clock error in the satellites.
Space Segment: The space-based component of the GPS system (i.e., the satellites).
User Segment: The component of the GPS system that includes the receivers.
Y-Code: Classified PRN code, similar to the P-code, though restricted to use by the military.
37
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Appendix B
U.S. EPA - Locational Data Policy
Locational Data Policy Implementation Guidance (LDPIG). 1991. U.S. EPA Office of Information
Management Resources, Washington, B.C.
1. Purpose: This policy establishes the principles for collecting and documenting latitude/longitude
coordinates for facilities, sites, and monitoring and observation points regulated or tracked under
Federal environmental programs within the jurisdiction of the Environmental Protection Agency
(EPA). The intent of this policy is to extend environmental analyses and allow data to be integrated
based upon location, thereby promoting the enhanced use of the EPA's extensive data resources for
cross-media environmental analyses and management decisions. This policy underscores the EPA's
commitment to establishing the data infrastructure necessary to enable data sharing and secondary
data use.
2. Scope and Applicability: This policy applies to all EPA organizations and personnel of agents
(including contractors and grantees) of the EPA who design, develop, compile, operate, or maintain
EPA information collections developed for environmental program support. Certain requirements of
this policy apply to existing as well as new data collections.
3. Background:
a. Fulfillment of the EPA's mission to protect and improve the environment depends upon
improvements in cross-programmatic, multimedia data analyses. A need for available and reliable
location identification information is a commonality which all regulatory tracking programs share.
b. Standard location identification data will provide a return yet unrealized on the EPA's sizable
investment in environmental data collection by improving the utility of these data for a variety of
value-added secondary applications often unanticipated by the original data collectors.
c. The EPA is committed to implementing its locational policy in accordance with the requirements
specified by the Federal Interagency Coordinating Committee for Digital Cartography (FICCDC).
The FICCDC has identified the collection of latitude/longitude as the most preferred coordinate
system for identifying location. Latitude and longitude are coordinate representations that show
locations on the surface of the Earth using the planet's equator and the prime meridian
(Greenwich, England) as the respective latitude and longitude origins.
d. The State/EPA Data Management Program is a successful multiyear initiative linking state
environmental regulatory agencies and the EPA in cooperative action. The program's goals
include improvements in data quality and data integration based on location identification.
38
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e. Readily available, reliable, and consistent location identification data are critical to support the
Agency-wide development of environmental risk management strategies, methodologies, and
assessments.
f. OIRM is committed to working with EPA Programs, Regions, and Laboratories to apply spatially
related tools (e.g., geographic information systems (GIS), remote sensing, automated mapping)
and to ensure these tools are supported by adequate and accurate location identification data.
Effective use of spatial tools depends on the appropriate collection and use of location identifiers
and on the accompanying data and attributes to be analyzed.
g. OIRM's commitment to effective use of spatial data is also reflected in the Agency's
comprehensive GIS Program and OIRM's coordination of the Agency's National Mapping
Requirement Program (NMRP) to identify and provide for the EPA's current and future spatial
data requirements.
4. Authorities:
a. 15 C.F.R., Part 6 Subtitle A, Standardization of Data Elements and Representations.
b. Geological Survey Circular 878-B, A U.S. Geological Survey Data Standard, Specifications for
Representation of Geographic Point Locations for Information Interchange.
c. Federal Interagency Coordinating Committee on Digital Cartography (FICCDQ/U.S. Office of
Management and Budget, Digital Cartographic Data Standards: In Interim Proposed Standard.
d. EPA Regulations 40 C.F.R 30.503 and 40 CPR 31.45, Quality Assurance Practices under the
EPA General Grant Regulations.
5. Policy:
a. It is EPA policy that latitude/longitude ("lat/long") coordinates be collected and documented with
environmental and related data. This is in addition to, and not precluding, other critical location
identification data that may be needed to satisfy individual program or project needs, such as
depth, street address, elevation, or altitude.
b. This policy serves as a framework for collecting and documenting location identification data. It
includes a goal that a 25-meter level of accuracy is achieved; managers of individual data
collection efforts determine the exact levels of precision and accuracy necessary to support their
mission within the context of this goal. The use of global positioning systems (GPS) is
recommended to obtain lat/longs of the highest possible accuracy.
c. To implement this policy, program data managers must collect and document the following
information:
(1) Latitude/longitude coordinates in accordance with Federal Interagency Coordinating
Committee for Digital Cartography (FICCDC) recommendations. The coordinates may be
present singly or multiple times, to define a point, line, or area, according to the most
appropriate data type for the entity being represented.
39
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The format for representing this information is:
t/-DD MM SS.SSSS (latitude)
t/-DDD MM SS.SSSS (longitude)
where:
• Latitude is always presented before longitude
• DD represents degrees of latitude; a two-digit decimal number ranging from 00 through
90
• DDD represents degrees of longitude; a three-digit decimal number ranging from 000
through 180
MM represents minutes of latitude or longitude; a two-digit decimal number ranging
from 00 through 60
SS.SSSS represents seconds of latitude or longitude, with a format allowing possible
precision to the ten-thousandths of seconds
• + specifies latitudes north of the equator and longitudes east of the prime meridian
- specifies latitudes south of the equator and longitudes west of the prime meridian
(2) Specific method used to determine the lat/long coordinates (e.g., remote sensing techniques,
map interpolation, cadastral survey)
(3) Textual description of the entity to which the latitude/longitude coordinates refers to (e.g.,
northeast corner of site, entrance to facility, point of discharge, drainage ditch)
(4) Estimate of accuracy in terms of the most precise units of measurement used (e.g., if the
coordinates are given to tenths-of-seconds precision, the accuracy estimate should be
expressed in terms of the range of tenths-of seconds within which the true value should fall,
such as "+/- 0.5 seconds")
d. Recommended labeling of the above information is as follows:
• "Latitude"
• "Longitude"
• "Method"
• "Description"
• "Accuracy"
e. This policy does not preclude or rescind more stringent regional or program-specific policy and
guidance. Such guidance may require, for example, additional elevation measurements to fully
characterize the location of environmental observations.
40
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f. Formats, standards, coding conventions, or other specifications for the method, description, and
accuracy information are forthcoming.
6. Responsibilities:
a. The Office of Information Resources Management (OIRM) shall:
(1) Be responsible for implementing and supporting this policy
(2) Provide guidance and technical assistance where feasible and appropriate in implementing and
improving the requirements of this policy
b. Assistant Administrators, Associate Administrators, Regional Administrators, Laboratory
Directors, and the General Counsel shall establish procedures within their respective organizations
to ensure that information collection and reporting systems under their direction are in compliance
with this policy.
While the value of obtaining locational coordinates will vary according to individual program requirements,
the method, description, and accuracy of the coordinates must always be documented. Such documentation
will permit other users to evaluate whether those coordinates can support secondary uses, thus addressing
EPA data sharing and integration objectives.
7. Waivers: Requests for waivers from specified provisions of the policy may be submitted for review
to the Director of the Office of Information Resources Management. Waiver requests must be based
clearly on data quality objectives and must be signed by the relevant Senior IRM Official prior to
submission to the Director, OIRM.
8. Procedures and Guidelines: The Findings and Recommendations of the Locational Accuracy Task
Force supplement this policy. More detailed procedures and guidelines for implementing the policy
are issued under separate cover as the Locational Data Policy Implementation Guidelines.
25 Meter Accuracy Goal
It has also established an Agency-wide accuracy goal of+/- 25 meters. The LDP +/- 25 meter accuracy
goal was written as a goal and not a standard because the achievement of a certain accuracy is based
primarily upon the best available data collection technology. The current best available technology, GPS,
allows for the acquisition of data with < 10 meter accuracy and has been embraced by the Locational
Accuracy Task Force (LATF) as the coordinate data collection technology of choice.
Method Accuracy and Description Codes
Along with the geographic coordinates, the LDP requires that associated Method, Accuracy, and
Description (MAD) codes accompany the spatial data sets. The Method, Accuracy, and Description
(MAD) code fields listed below are outlined in the Method, Accuracy, and Description (MAD) codes v 6.1.
The document represents a procedure for standardizing the coding of geographic information and
associated attributes for use in a geographic information system (GIS) or other statistical software
program. It requires that all geographic coordinates acquired by Agency employees, contractors, and
grantees be accompanied by the following information.
41
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Required Locational Data Fields Required Locational Data Fields
1. Latitude (represented in decimal degrees +/- dd.xxxxxx)
2. Longitude (represented in decimal degrees +/- ddd.xxxxxx)
3. Method of collection
4. Accuracy value and unit
5. Description category
6. Vertical measure
7. Horizontal datum
8. Source scale
9. Feature type (point - line - area)
Recommended/Optional Locational Data Fields
1. Date of collection
2. Source
3. Description comments
4. Vertical measure method of collection
5. Vertical measure accuracy
6. Vertical datum
7. Verification
8. Data-point-sequence
9. Description-sequence
10. Lat/Long Policy
42
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Appendix C
Examples of GPS in Environmental Applications
New Jersey Department of Environmental Protection Assesses Water Quality
The New Jersey Department of Environmental Protection has been using GIS to assess water quality of the
state's major river basins and to communicate its findings to local governments, community groups, and
businesses. The department studies entire watersheds, so scientists, planners, and regulators can
understand all sources of contamination and can work together to restore water quality.
Scientists collected samples from the Whippany River which is located near an urban area. The Whippany
watershed receives pollution from sewage treatment plants, factories, farms, and storm water runoff.
Scientists took samples of the river's sediment and water and measured the concentrations of nutrients,
organics, and metals. They also took readings of temperature, dissolved oxygen, and pH. The data were
compared to standards set by state and Federal agencies to keep the waters clean enough to provide healthy
fish habitats and to provide swimming opportunities for the public.
The scientists also collected biological samples, looking in particular for creatures sensitive to pollution. If
the samples are composed mostly of animals that can tolerate pollution, or if the number and types of
insects are different from past samples, the scientists are alerted to changes in water quality, change that
could be missed by chemical sampling alone.
As samples were collected, the researchers collected their exact field positions with GPS receivers. These
positions, along with their associated chemical and biological data, were used in a GIS to create a map of
the watershed's streams and lakes. Other map layers were added. One was a layer of potential sources of
pollution, representing locations, such as factory sites, where pollutants are known to be discharged. The
inclusion of land use data made it possible to take into account more diffuse types of pollution, like that
from farms and storm runoff. The GIS was queried to determine the proximity of known sites of
contamination to the rivers and streams being monitored. Finally, the biological sampling data was added
and the GIS was used to show impairment ratings for stream segments. The impairment rating is a
measure of the health hazard it poses to fish and human swimmers.
Given this information, the department was able to find the severely impaired segments and take action.
The department did this by going into the field and checking for possible causes of this severe
contamination. Further water sampling was also done to help the regulators determine where the
contamination was entering the stream. With all the collected information, the polluter was identified for
being a leaking storage tank at a nearby factory.
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Portland. Maine Quicky Improves Infrastructure Management
Like many old cities, Portland had much old infrastructure data that was not accurately reported in the
city's paper records or incorporated in the city's growing GIS. The GIS coordinator for Portland wanted a
one-person data gathering system that was quick, affordable, and database ready. The impetus for
developing this system occurred when city officials asked the engineering section to supply detailed
information about the condition and location of the city's culverts as part of the city's participation in
Project Impact, a Federal Emergency Management Agency (FEMA) program designed to minimize and
prevent damage resulting from disasters. However, extensive culvert information was not readily available
in the city's database records.
The engineering section responded by acquiring a GPS/GIS two-way data collection system. This unit
enabled users to accurately create and edit submeter accuracy position or attribute data in the field. For
this culvert project, the team divided the city into sections and created paper maps of culvert locations
gleaned from existing city records. Based on information from these maps, a mapping technician began
inspecting streets with recorded culverts and attempted to locate unrecorded culverts. Once a culvert was
found, the position of the inlet and outlet were recorded, in most areas, to submeter accuracy.
Portland also planned to periodically reinspect the culverts. Survey crews were usually sent out in teams of
two when operating more conventional systems. With the GPS units, it became a one-person job. In
addition, when it was time for reinspection, the culverts were located in less time because they were all
clearly marked and the GPS units were used to guide them back to the locations.
44
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Appendix D
IRM Policy Manual 2100 CHG 2
1. Purpose: This policy establishes the principles for collecting and documenting latitude/longitude
coordinates for facilities, sites, and monitoring and observation points regulated or tracked under
Federal environmental programs within the jurisdiction of the Environmental Protection Agency
(EPA). The intent of this policy is to extend environmental analyses and allow data to be integrated
based upon location, thereby promoting the enhanced use of the EPA's extensive data resources for
cross-media environmental analyses and management decisions. This policy underscores the EPA's
commitment to establishing the data infrastructure necessary to enable data sharing and secondary
data use.
2. Scope and Applicability: This policy applies to all Environmental Protection Agency (EPA)
organizations and personnel of agents (including contractors and grantees) who design, develop,
compile, operate, or maintain EPA information collections developed for environmental program
support. Certain requirements of this policy apply to existing as well as new data collections.
3. Background:
• Fulfillment of the EPA's mission to protect and improve the environment depends upon
improvements in cross programmatic, multimedia data analyses. A need for available and reliable
location identification information is a commonality which all regulatory tracking programs share.
• Standard location identification data will provide a return yet unrealized on the EPA's sizable
investment in environmental data collection by improving the utility of these data for a variety of
value-added secondary applications often unanticipated by the original data collectors.
• The EPA is committed to implementing its locational policy in accordance with the requirements
specified by the Federal Interagency Coordinating Committee for Digital Cartography (FICCDC).
The FICCDC has identified the collection of latitude/longitude as the most preferred coordinate
system for identifying location. Latitude and longitude are coordinate representations that show
locations on the surface of the Earth using the planet's equator and the prime meridian
(Greenwich, England) as the respective latitude and longitude origins.
• The State/EPA Data Management Program is a successful multiyear initiative linking state
environmental regulatory agencies and EPA in cooperative action. The program's goals include
improvements in data quality and data integration based on location identification.
• Readily available, reliable and consistent location identification data are critical to support the
Agency-wide development of environmental risk management strategies, methodologies and
assessments.
• OIRM is committed to working with EPA Programs, Regions, and Laboratories to apply spatially
related tools (e.g., geographic information systems (GIS), remote sensing, automated mapping)
and to ensure these tools are supported by adequate and accurate location identification data.
45
-------
Effective use of spatial tools depends on the appropriate collection and use of location identifiers,
and on the accompanying data and attributes to be analyzed.
• OIRM's commitment to effective use of spatial data is also reflected in the Agency's
comprehensive GIS Program and OIRM's coordination of the Agency's National Mapping
Requirement Program (NMRP) to identify and provide for the EPA's current and future spatial
data requirements.
4. Authorities:
1. 15 C.F.R., Part 6 Subtitle A, Standardization of Data Elements and Representations
2. Geological Survey Circular 878-B, A U.S. Geological Survey Data Standard, Specifications for
Representation of Geographic Point Locations for Information Interchange
5. Federal Interagency Coordinating Committee on Digital Cartography (FICCDC)/U.S. Office of
Management and Budget, Digital Cartographic Data Standards: An Interim Proposed Standard 6.
EPA Regulations 40 C.F.R. 30.503 and 40 C.F.R. 31.45, Quality Assurance Practices under the
EPA General Grant Regulations.
5. Policy:
a. It is EPA policy that latitude/longitude ("lat/long") coordinates be collected and documented with
environmental and related data. This is in addition to, and not precluding, other critical location
identification data that may be needed to satisfy individual program or project needs, such as
depth, street address, elevation, or altitude.
b. This policy serves as a framework for collecting and documenting location identification data. It
includes a goal that a 25-meter level of accuracy is achieved; managers of individual data
collection efforts determine the exact levels of precision and accuracy necessary to support their
mission within the context of this goal. The use of global positioning systems (GPS) is
recommended to obtain lat/longs of the highest possible accuracy.
c. To implement this policy, program data managers must collect and document the following
information:
(1) Latitude/longitude coordinates in accordance with Federal Interagency Coordinating
Committee for Digital Cartography, (FICCDC) recommendations. The coordinates may be
present singly or multiple times, to define a point, line, or area, according to the most
appropriate data type for the entity being represented.
The format for representing this information is:
+/-DD MM SS.SSSS (latitude)
+/-DDD MM SS.SSSS (longitude)
where:
i. Latitude is always presented before longitude
ii. DD represents degrees of latitude; a through 90
iii. ODD represents degrees of longitude; a ranging from 000 through 180
iv. MM represents minutes of latitude or from 00 through 60
46
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v. SS.SSSS represents seconds of latitude or precision to the ten-thousandths of seconds
vi. "+" specifies latitudes north of the equator and longitudes east of the prime meridian
vii. "-" specifies latitudes south of the equator and longitudes west of the prime meridian
(2) Specific method used to determine the lat/long coordinates (e.g., remote sensing techniques,
map interpolation, cadastral survey)
(3) Textual description of the entity to which the latitude/longitude coordinates refers to (e.g.,
northeast corner of site, entrance to facility, point of discharge, drainage ditch)
(4) Estimate of accuracy in terms of the most precise units of measurement used (e.g., if the
coordinates are given to tenths-of-seconds precision, the accuracy estimate should be
expressed in terms of the range in tenths-of-seconds within which the true value should fall,
such as "+/- 0.5 seconds")
I. Recommended labeling of the above information is as follows:
a. "Latitude"
i. "Longitude"
ii. "Method"
hi. "Description"
iv. "Accuracy"
b. This policy does not preclude or rescind more stringent Regional or program-specific
policy and guidance. Such guidance may require, for example, additional elevation
measurements to fully characterize the location of environmental observations.
c. Formats, standards, coding conventions or other specifications for the method,
description, and accuracy information are forthcoming.
6. Responsibilities:
a. The Office of Information Resources Management (OIRM) shall:
(1) Be responsible for implementing and supporting this policy.
(2) Provide guidance and technical assistance where feasible and appropriate in implementing and
improving the requirements of this policy.
b. Assistant Administrators, Associate Administrators, Regional Administrators, Laboratory
Directors, and the General Counsel shall establish procedures within their respective organizations
to ensure that information collection and reporting systems under their direction are in compliance
with this policy.
While the value of obtaining locational coordinates will vary according to individual program
requirements, the method, description, and accuracy of the coordinates must always be
documented. Such documentation will permit other users to evaluate whether those coordinates
can support secondary uses, thus addressing EPA data sharing and integration objectives.
47
-------
7. Waivers:
Requests for waivers from specified provisions of the policy may be submitted for review to the
Director of the Office of Information Resources Management. Waiver requests must be based
clearly on data quality objectives and must be signed by the relevant Senior IRM Official prior to
submission to the Director, OIRM.
8. Procedures and Guidelines: The Findings and Recommendations of the Locational Accuracy Task
Force supplement this policy. More detailed procedures and guidelines for implementing the policy
are issued under separate cover as the Locational Data Policy Implementation Guidelines.
LRT Return Format
The Locational Reference Tables (LRT) serve as a repository for locational information that has been
collected and documented as a result of the EPA Locational Data Improvement Project. The LRT are a
series of tables that store facility-level locational information collected from the program system databases
in Envirofacts and from the EPA regional data stewards. This information includes geographic attributes,
coordinate data, and Method, Accuracy, and Description (MAD) qualifiers.
To design the LRT, the EPA solicited feedback from regional and program office stakeholders in regular
LDIP meetings. A requirements document was drafted based on this input, and the LRT was designed and
released in February 1997 to serve as a repository of latitude and longitude coordinates and associated
documentation. The original data load consisted of latitude and longitude coordinates acquired as a result
of geocoding. These tables were synchronized with the Envirofacts refresh process to be updated monthly,
and it served as the source for spatial data used to depict EPA-regulated facilities in GIS applications
developed within the EPA. To access the LRT, go to:
http://www.epa.gov/enviro/html/locational/index.html.
Sample Letter of Introduction
Note: All letters requesting access to property should be on official stationary, include both a day and
evening phone number, and any other appropriate information. The example on the next page has
been used by an Agency contractor.
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July 4, 1991
To Whom it May Concern,
The below named individuals are employees of the Bionetics Corporation and under contract to the
U.S. Environmental Protection Agency (contract Number 68-03-3532). These individuals will be
collecting field data in the area of Chattanooga, Tennessee, during the month of November 1990:
Mary Brown
Bill Johnson
John Smith
Their efforts are in support of official U.S. Environmental Protection Agency research. Please extend
them all possible courtesy and consideration.
Additional information may be obtained by calling (703) 349-8970.
Sincerely,
E. Terrence Slonecker
Environmental Scientist
U.S. Environmental Protection Agency
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Pre-survey Checklist
Obtain List of Facilities
Obtain Current Almanac
Call Coast Guard to Verify Satellite Availability
Obtain Control Points from NGS or Local Source
Obtain 7.5 min Topographic Maps
Obtain Local Street Maps
Prepare Letter of Introduction
Collect and Pack Field Equipment
Field Equipment
GPS Equipment
Laptop or Other Field Computer
7.5 min Maps
Aerial Photo if Available
Camera
Film
Compass
Tape Measure
Binoculars
Field Forms
Clip Board
Calculator
GPS Hardware/Software Manuals
Mini Tape Recorder
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Field Equipment, Continued
Hard Copy of Almanac
Rain Gear
Two-way Radio Communication (i.e., CB, cellular phone, etc.)
Last Minute Checks
Charge Batteries
Verify Almanac
Target Travel Route
In the Field Checks
Find Base Stations
Initialize Equipment
Begin Collecting Data
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United States
Environmental Protection
Agency
Please make all necessary changes on the below label,
detach or copy, and return to the address in the upper
left-hand corner.
If you do not wish to receive these reports CHECK HERE
PRESORTED STANDARD
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Office of Research and Development
National Exposure Research Laboratory
Environmental Sciences Division
P.O. Box 93478
Las Vegas, Nevada 89193-3478
Official Business
Penalty for Private Use
$300
EPA/600/R-02/031
April 2002
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