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            Office of
   Environmental Information

Global  Positioning Systems
 Technical Implementation
          Guidance

         (September 2003)
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OFFICE OF
ENVIRONMENTAL
INFORMATION

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                                                   EPA/2 50/R-03/001
                                                    September 2003
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    Global  Positioning  Systems
       Technical  Implementation
                       Guidance
                           Project Lead

                       George M. Brills, Chair
                   U.S. EPA Geospatial Quality Council
         Tim Bridges
         EPA, Region 1

         George M.  Brilis
         EPA, ORD

         Wendy Blake-
         Coleman
         EPA, OEI

         David Hansen
         DOI, BoR

         Chad Cross
         EPA, ORD

         Ivan DeLoatch
         EPA, OEI
                  Authors

                  Timothy Drexler
                  EPA, Region 5

                  Karl Hermann
                  EPA, Region 8

                  Patricia Hirsch
                  EPA, OGC

                  Cheryl  Itkin
                  EPA, ORD

                  Shashank Kalra
                  EPA, OEI
                  Linda Kirkland
                  EPA, OEI
              Kevin Kirby
              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
Michael Glogower
EPA, Region 2
                        Peer Reviewers
      Dan Harris
      EPA, Region 7
Nita Tallent-Halsell
EPA, ORD
John G. Lyon
EPA, ORD
David Burden
EPA, ORD
                  U.S. Environmental Protection Agency
                   Office of Research and Development
                    Environmental Sciences Division
                        Post Office Box 93478
                    Las Vegas, Nevada 89193-3478
                                                     3260DC03.RPT
                                                                 10/31/03

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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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                                          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 trade
names or commercial products does not constitute endorsement or recommendation for use.

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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 have 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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                                         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.

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. In order

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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 (LDPIG, 1992)." 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 HI et al.
and is a testament to the timelessness of his work.
George M. Brilis, Chair
EPA Geospatial Quality Council

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                                     Background
The U.S. EPA Geospatial Quality Council (GQC) was formed in 1998 to provide Quality Assurance (QA)
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, the EPA Geospatial Quality Council Strategy
Plan. The GQC is dynamic and continually improving the foundation of quality in the use of geospatial
science. Individuals and organizations should periodically check the GQC website for additional products
and updates, http://www.epa.gov/nerlesdl/gqc/default.htm In addition to this document the GQC website
also contains a training course, "GIS for QA Professionals" and the EPA Guidance for Geospatial-related
Quality Assurance Project Plans, EPA/240/R-03/003.  Operating without a budget, all products of the GQC
are created from through the voluntary efforts of the members.

An internal 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
re search 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
Technology 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. The
GIS Technical Memorandum 3 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.

Trimble Navigation Limited graciously approved the use of all images/figures contained in this document.
All figures/images are copyrighted by Trimble and used by permission [McNabb,  July 2, 2002].

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                              Table  of Contents


Foreword	 vi

Background	 viii

Acknowledgments  	 ix


Section I    Introduction	1
   Purpose of Document and Intended Audience	1
   Document Contents  	2
   Document Updates	3

Section IIAlternative Methods of Geopositioning	6
   Conventional Surveying	6
   Methods of Point Surveying	7

Section m  Global Positioning System (GPS) Technology	8
   Methods of Satellite Positioning	11
      Autonomous	11
      Differential	11
      Wide Area Augmentation System (WAAS)	12
      GPS and GIS  	13
      GPS: Direct and Secondary Data	13

Section IV  Quality Assurance Considerations	14
   Overview of QA Project Plan Requirements  for Geospatial Data	14
      Graded Approach	15
      EPA QA Requirements	15
      Project Design Criteria  	16
      Accuracy and Precision  	16
      Factors Affecting the Accuracy of the GPS Survey	17
         Multipath	17
         Atmospheric Delays	17
         Baseline Length	18
         Position Dilution of Precision (PDOP)	18
         Signal-to-Noise Ratio (SNR)	18
   Data Quality Indicators and General Requirements	18
         Accuracy and Precision Requirements 	18
         Multipath Avoidance Requirements  	19
         Metadata File Collection Requirements 	19
         Satellite Detection and Position Requirements	19

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Table of Contents, Continued
         Atmospheric and Ratio Requirements	20
         Base Station Distance Requirements	20
         Calibration Requirements	20
         Completeness Requirements	21
         Data Collection Time and Frequency Requirements  	21
         Data Evaluation	21

Section V    Core Elements of GPS Standard Operating Procedures	22
   Planning and Preparation	22
      Planning and Implementing a GPS Survey	22
      Pre-survey Planning  	22
      Define Objectives of Survey  	23
      Define Project Area	23
      Determine Observation Window and Schedule Operations	23
      Establish Control Configuration  	24
      Select Survey Locations  	25
      Equipment Logistics	25
   Reconnaissance 	26
      Locate and Verify Control Point Locations  	26
      Preview Instrument Locations	26
      Physically Establish Point Locations	26
   Survey Execution	26
      Establishing a Schedule of Operations	26
      Pre-survey: The Day Before	26
      Pre-data Collection: Establishing a Base Station	27
      Data Collection:  Performing the GPS Survey	27
   Returning from the Field	27
      Data Transfer	28
      Initial Processing	28
      Computation	28
      Data Conversion to GIS  	29
      Documentation and Reporting	29

Section VI   Management of Locational Data	31

Section VII   Legal Considerations	34
   Collection of Data  	34
   Storage and Maintenance of Data	34
   Release of Data Pursuant to Freedom of Information Act Requests	34
   Privacy Concerns	35
   A-110 	35
   Data as Confidential Business Information	36
   Toxics Release Inventory (TRI)  	36
   Locational Data as Intellectual Property	36

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Table of  Contents, Continued

Section VIII   References	37
Appendix A  Glossary of GPS Terms	40
Appendix B  Examples of GPS in Environmental Applications	42
Pre-survey Checklist 	44
Sample Letter of Introduction	46

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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, and

  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 who 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 staff or 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
      currently 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 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 EPA's
information management.

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The accuracy required for GPS data collection will vary depending on the reasons for gathering locational
informatioa Different equipment and procedures are needed to identify the outline of a landfill than those
needed to determine the location of a ground-water monitoring well used for a hydrologic 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 both the EPA Locational Data Policy and the Federal
Geographic Data Committee's  (FGDC) Content Standard for Digital Geospatial Metadata.  Federal
agencies are required to follow the FGDC standard according to Executive Order  12906, "Coordinating
Geographic Data Acquisition and Access: The National Spatial Data Infrastructure."


Document Updates

This document  is intended to be a "living document."  Two EPA organizational units will work together to
update and release revisions. These organizational units are both within the EPA's Office of
Environmental Information, Office of Information Collection (OIC). The duties and responsibilities of the
organizational units overseeing this document are both within the OIC.  The units within the OIC  are, the
Data Acquisition Branch (DAB), and the Data Standards Branch (DSB). The revelant duties of each of
these units are described below.

The Office of Information Collection (OIC): develops and implements innovative data collection policies
and services. The Office promotes the efficient and effective collection and use of data and develops
processes to ensure that environmental data and information meet established standards of quality.
http://www.epa.gov/oei/collecting.htm

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Data Acquisition Branch (DAB): is responsible for working with the Agency's partners at the Federal and
state levels on data sharing and exchange projects via electronic and non-electronic means. Functions of
the Branch that are relevant to this document are as follows:

   •  Provide strategic direction, guidance and standards, and support for the geospatial program (remote
      sensing, Geographic Information Systems,  spatial enablement of data and information systems, and
      visualization) within the Agency and oversee their implementation.

   •  Obtain and manage, on behalf of the Agency, environmental data from third party sources (especially
      other federal agencies such as the United States Geological Survey, USGS);

   •  Manage and/or participate in standing coordinating committees (with states, other Federal Agencies,
      other countries, and non-governmental entities or other organizations) that facilitate joint strategic
      and multi year planning for data acquisition and expedite related technology and information
      exchange;

   •  Work with the states,  tribes, and other government organizations to integrate and share data through
      current and other emerging and innovative  approaches.

   •  Identify, obtain, and broker data sets with environmentally-relevant information, including non-
      regulatory data (such as spatial data and "orphan" data sets). Manage EPA Interagency Agreements
      for data acquisition.

The Data Standards Branch (DSB): is responsible for maintaining a current and comprehensive
understanding of the Agency's data architecture,  i.e., the "what" and "where" aspects of EPA's data
holdings. Functions of the Branch that are relevant to this document are as follows:
http://oaspub.epa. gov/edr/EPASTD$. STARTUP

   •  In concert with state partners, develop and implement standards for the Environmental Data Registry
      (EDR). http ://www. epa. gov/edr/

   •  Develop and oversee the data standards program, including monitoring, measurement, and metadata.

   •  Develop and oversee the implementation of Agency-wide business rules for new and existing data
      standards, in concert with the Environmental Council of the States (ECOS).

   •  Lead the design and implementation of the EPA Facility Registry System.

   •  Participate in cooperative data standard-setting activities for international environmental information.

   •  Develop and publish the semi-annual Agency Information Inventory.

   •  Develop and oversee the implementation of Agency information protection policies,  including policies
      for central docket, confidential business information CBI, and Privacy Act implementation.

   •  Serve as the Agency Records Officer and oversee the National Records  Management Program,
      including the Agency History Program.

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Distribution of document revisions may be a time consuming process.  Therefore, readers are encouraged to
check the organizational website listed above for the latest update in standards and data collection.

The EPA Geospatial Quality Council (GQC) is available to all for consultation and assistance. At the time
of this writing, the GQC website is being developed.  GQC contact information is provided at the beginning
of this document.

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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 and distance between points 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. gov/1 and are searchable by area as well as site name. In addition, there is a netwot
of continuously operating reporting stations (CORS) Fhttp://www.ngs.noaa. gov/CORS/1. 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 allow it to calculate a position:

   1. The space segment - approximately 24 NAVSTAR satellites.

   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 positioa 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 a sphere

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centered around the satellite, with the radius
representing the range between the satellite and the
receiver antenna (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).
One measurement narrows down our
 position to the surface of a sphere
                                We are on the
                                surface of this
                                sphere
                  Figure 1
          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
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.

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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
the observer to the satellite.
                                         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
                                                                 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).
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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 satellite's
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.
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 navigatioa 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 are 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

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    sites should occur shortly after the GPS data are collected in the field to be able to match the same time
    frame as the data collected in the field.

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.

Wide Area Augmentation System (WAAS)
Wide Area Augmentation System (WAAS) is a GPS  signal correction system being  developed by the
Federal Aviation Administration (FAA) and the Department of Transportation for use in precision aircraft
flight approaches. Currently,  GPS alone does not meet the FAA's navigation requirements for accuracy,
integrity and availability. WAAS corrects for GPS signal errors that can be caused by ionospheric
disturbances, timing and satellite orbit errors as well  as the integrity and health of each of the GPS satellites.
WAAS is not expected to be approved by the FAA for a  couple of years but the system is available for
civilian use, such as for boaters and recreational GPS users.

The existing WAAS network consists of approximately 25 ground reference stations positioned across the
United States that monitor GPS satellite data. These data are collected by two master stations, located on
either coast and in turn create  a GPS correction message. This correction accounts for GPS satellite orbit
and clock drift plus signal delays caused by the atmosphere and ionosphere. The corrected differential
message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over
the equator. The information  is compatible with the basic GPS signal structure, which means any WAAS-
enabled GPS receiver can read the corrected signal.

Any GPS unit that is WAAS enabled can receive these more accurate corrected signals.  Many inexpensive
GPS units are available on the market that are WAAS enabled. Currently, WAAS satellite coverage is only
available in North America. For some users in the U. S., the position of the satellites over the equator makes
it difficult to receive the  signals when trees, buildings, or mountains obstruct the view of the horizon. WAAS
signal reception is ideal for open land and marine applications. WAAS provides extended coverage both
inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of WAAS
is that it does not require additional receiving equipment while DGPS does.

GPS Accuracy:

 100 meters: Accuracy of the  original GPS system, which was subject to accuracy degradation under the
            government-imposed Selective Availability (SA) program.

  15 meters: Typical GPS position accuracy without SA.

 3-5 meters: Typical differential GPS (DGPS) position accuracy.

 < 3 meters: Typical WAAS position accuracy
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GPS and CIS
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 these data
collection tools.  After post processing, these features can be exported to a number of GIS formats and used
for analysis with other spatial data.

GPS: Direct and  Secondary Data

     Direct: This document is intended to address the approach for directly obtained GPS data, such as
            during  surveys or other collection events or activities.

 Secondary: Caution should be exercised by the user in that GPS results are frequently more accurate than
            available base map information.
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                                       Section  IV

                  Quality  Assurance Considerations
This guidance supplements EPA Guidance for Geospatial Data Quality Assurance Project Plans (Peer
Review Draft), (EPA QA/G-5G), in that the focus here is to guide the process of collecting, editing, and
exporting accurate spatial data using the Global Positioning System (GPS).

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 plaa  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).  The EPA Guidance for
Geospatial Data Quality Assurance Project Plans (Peer Review Draft), (EPA QA/G-5G) 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 EPA 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 the EPA Guidance for Geospatial Data Quality Assurance Project
Plans (Peer Review Draft), (EPA QA/G-5G) 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/ASQC E4,  1994), as cited in contract and assistance agreement regulations and incorporated in the
revised EPA Order 5360.1 A2 (EPA 2000) and the EPA Manual 5360 Al (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

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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 and the multitude of stakeholders.  For this reason, a tiered approach to accuracy values  for
locational information is being considered for the Agency's location data.  With respect to GPS information,
this underscores the importance of documenting the GPS collection method used to collect coordinate data
(see Latitude/Longitude Data Standard at http://www.epa.gov/edr/).

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  A2 (2000), Policy and Program Requirements for the Mandatory
Agency-wide Quality System, and the EPA Manual 5360 Al  (2000), EPA 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 ofthe 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 EPA Manual 5360 Al  (2000), 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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"QA Project Plans Requirements" are provided in Chapter 5 of the EPA 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 must be considered in
project planning with the EPA QA/G-5 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/6OO/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 Quality System 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  (PLGR)
which use the encrypted Y code. This improves the accuracy of these hand-held units particularly where

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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 are collected with Standard Operating
Procedures that specify exactly how the data are 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 are 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 Guidance for Geospatial Data Quality
Assurance Project Plans (Peer Review Draft), (EPA QA/G-5G), Sampling Process Design, Section 2.2.1,
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 reduced position accuracy [http://www.trimble.com/gps/1. Water vapor in
the troposphere  and atmospheric pressure may also have a slight affect on the accuracy of a GPS position.
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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.

   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).
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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 so that the GPS antenna sees the sky
from 45 degrees and above.

Metadata File Collection Requirements
While it is recognized that many recreational grade units are typically not capable of storing in memory
essential method, accuracy, and description values that are required by the Latitude/Longitude Data
Standard (L/LDS) each coordinate point collected with a GPS is still required to document this information.
It is for this reason that recreation grade units are not encouraged, except where no other option exists for
collecting locational data. For mapping grade and survey grade units, the following information should be
saved to file in addition to the standard metadata required by the L/LDS:

   1.  Correction status,
   2.  GPS unit type,

   3.  PDOP, and
   4.  Standard deviation of points.

All of these data provide 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 EPA 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 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 are 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

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units already reflect this limitatioa  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 and where practicable and
possible, 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 always appropriate to require the highest accuracy to be attained,
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 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 project goals, the data are 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

   •  Objectives of the survey

   •  What features will be mapped, sample point location identification, and how they should be
      represented (points, lines, areas)

   •  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

   •  The presence of any obstructions to satellite signals such as buildings or tree canopies

   •  The necessity of a data dictionary

   •  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

   •  The need to use external sensors such as laser range finders, digital cameras, or depth finders

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

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(see the reference section). These site descriptions can be added to a data dictionary as feature attributes
and installed on a GPS receiver or data collector.

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 used 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
approximately 24 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
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.
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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 horizoa  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, 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, if
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 are 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.

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.
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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 as well as by zip code.
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 are 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 are 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 Quality System 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, utilizing, if practical, the
descriptive reference points listed in the L/LDS, as this information will be required in the subsequent input
of coordinate information in the Locational Reference Tables . 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 ofreproducible
markings.


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.

Special note: Recreational GPS Units
Whereas taking 35-40 readings may be appropriate for sub-meter survey-grade accuracy, this may not be
appropriate for recreational units. Recreational GPS units are widely used by some EPA Programs and
stakeholders. The Agency is currently developing standards for recreational units. Though this is intended
to be a living document, the reader is encouraged to check the web site for the latest changes in standards,
especially recreational units. http://oaspub.epa.gov/edr/epastd$.startup

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 laptop 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.
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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 are 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.

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.
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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,
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 are established in the Agency's
Latitude/Longitude Data Standard (L/LDS). This data standard draws elements from both the EPA
Locational Data Policy and the Federal Geographic Data Committee's (FGDC) Content Standard for
Digital Geospatial Metadata.

The Latitude/Longitude Data Standard establishes the requirements for documenting latitude and longitude
coordinates, and related method, accuracy and description data for places of interest to the Agency. Places
include facilities, sites, monitoring stations, observation points, and other features regulated or tracked under
federal environmental programs within the jurisdiction of the EPA The intent of this standard is to ensure
that sufficient information is available with each set of locational data to enable an assessment of the
precision and accuracy of that data. Mandatory  reporting data elements include:

Latitude Measure: Expressed in Degrees and decimal degrees (DD.dddddd)

Longitude Measure: Expressed in Degrees and decimal degrees (DD.dddddd)

Horizontal Collection Method: Describes the method used to determine coordinates.  GPS methods
currently recognized include:
        Horizontal  Collection
        Method

        GPS Carrier Phase Static
        Relative Position


        GPS Carrier Phase
        Kinematic Relative Position
        GPS Code (Pseudo Range)
        Differential
        GPS Code (Pseudo Range)
        Precise Position
        GPS Code - Autonomous,
        Recreation class unit (new
        method proposed)


        GPS, with Canadian Active
        Control System


        GPS-Unspecified
Definition
The geographic coordinate determination method
based on GPS carrier phase static relative
positioning technique

The geographic coordinate determination method
based on GPS carrier phase kinematic relative
positioning technique.

The geographic coordinate determination method
based on GPS carrier phase kinematic relative
positioning technique.

The geographic coordinate determination method
based on GPS code measurements (pseudo range)
precise positioning service.

The geographic coordinate determination method
based on GPS position calculated by one receiver
at an unknown  location with a recreation class
unit

The geographic coordinate determination method
based on GPS code measurements (pseudo range)
using the Canadian Active Control System

Global Positioning Method, with unspecified
parameters.
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Horizontal Accuracy Measure: The measure of the accuracy (in meters) of the coordinates

Reference Point: The text (or code) that identifies the place for which the geographic coordinates were
established

Horizontal Reference Datum: The name (or code) that describes the reference datum used to determine the
geographic coordinates. Note: GPS methods should specify WGS84.

For further reference to the Agency's adopted Latitude/Longitude Data Standard, please go to
http://www.epa.gov/edr/ and follow the prompts to the final data standards.

Federal agencies are required to follow the FGDC standard according to Executive Order 12906,
"Coordinating Geographic Data Acquisition and Access: The National Spatial Data Infrastructure."
Information on the policy and standard as well as assistance with the reporting requirements can be obtained
from the EPA Envirofacts website, www.epa.gov/enviro/, or the FGDC website, www.fgdc.gov.

EPA established a Locational Data Policy (OIRM Policy 2100, 8 April 1991) to communicate 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. This accuracy
goal was established to achieve an optimal accuracy 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 method technology of choice.
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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 are of sufficient quality for intended uses.

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 the 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 the 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. Experience also suggest that it
is often critical to  record not only the typical MAD code information but also the results of verification or
other comparisons. This helps provide users with some assurance that data entry or conversion errors have
not occurred.

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.

Although the LDIP has improved the EPA's locational data,  challenges still remain. To address these
challenges and other concerns of locational data, the Locational Data Improvement Subcommittee (LDIS)


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was established in March 2001.  The vision of the LDIS, as stated in its Action Plan, is to ensure that
locational data are 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 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 metadata initiative, the complex FGDC
Content Standard 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/.

LRT Return Format:
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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.

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 Plaa The Agency has advocated an Agency-wide accuracy goal of 25-
meters.  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 are 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 are 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

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agency-created documents that have been requested and released available electronically if the agency
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 possessioa Once records have been identified as
responsive to a 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.usdoi. 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-1 10

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-110  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-110 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 a 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 these data are currently publicly available.


Locational Data  as Intellectual  Property

Under the Copyright Act, 17 U.S.C. § 101  et. seq., data are not generally subject to copyright protectioa
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 are 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.
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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.

American National Standards Institute.  Specifications and Guidelines for Quality Systems for
    Environmental Data Collection and Environmental Technology Programs. ANSI/ASQC E4, 1994.

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.

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.

Hartl, P. H. Remote Sensing and Satellite Navigation:  Complementary Tools of Space Technology.
    Photogrammetric Record, vol. 13:74, pp. 263-275, 1989.

Hum, J. GPS, A Guide to the Next Utility. Trimble Navigation Ltd., Sunnyvale, California, 1989, 76 pp.

Kruczynski, L. R.  Differential GPS: A Review of the Concept and How To Make It Work. Trimble
    Navigation Ltd., study report, 1990.

Kruczynski L. R., W. W. Porter, D. G. Abby, andE. T. Weston. Global Positioning System Differential
    Navigation Test at the Yuma Proving Ground. The Institute of Navigation, 1986.

Kruczynski, L. R. and A. F. Lange.  Geographic Information Systems and the GPS Pathfinder System:
    Differential Accuracy of Point Location Data.  Trimble Navigation Ltd., study report, 1990.

Lang, Laura. Managing Natural Resources with GIS.  Redlands, California, ESRI, Inc., 1998.
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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, 1989,4pp.

Langely, R. B. Innovation Column: Why is the GPS Signal So Complex?  GPS World, Vol. 1:3, pp. 56-
    59, 1990.

Leick, Alfred. GPS Satellite Surveying, 2nd Editioa New York: John Wiley & Sons, 1995.

McDonald, K. D.  GPS Progress and Issues.  GPS World, Vol. 1:1, p.  16, 1990.

McDonald, K. D.,  E. Burkholder, B. Parkinson, and 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.

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. Mapping Systems (Figures).  General Reference. P/N 24177. Revision B,
    1996.

Trimble Navigation Limited. A New Level of Accuracy for Differential GPS Mapping Applications Using
    EVEREST! Multipath Rejection Technology. Mapping and GIS Systems  Division. Document #102.
    pp. 1 - 7, 1997.

U.S. Department of Defense/Department of Transportation. 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,  1984.

U.S. Environmental Protection Agency. Locational Data Policy, IRM  Policy Manual, Chapter 13, 2100
    Chg 2, Office of Administration and Resources Management, 1991.

U.S. Environmental Protection Agency. Locational Data Policy Implementation Guidance (LDPIG). Office
    of Administration and Resources Management, PM-211D, 220 B-92-008, Washington, D.C., 1992.

U.S. Environmental Protection Agency. GIS Technical Memorandum  3: Global Positioning Systems
    Technology and its Application in Environmental Programs,  Office of Research and Development (PM-
    225).  EPA/600/R-92/036,  1992.
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U.S. Environmental Protection Agency. Method Accuracy Description (MAD) code 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, 1994.

U.S. Environmental Protection Agency. Locational Data Improvement Project Plan, Office of
    Administration and Resources Management, Contract Number 68-WI-0055.  Delivery Order Number
    065, Prepared by: EPA Systems Development Center. SDC-0055-065-JB-5057A, 1996.

U.S. Environmental Protection Agency. EPA Quality Manual for Environmental Programs, EPA Manual
    5360 Al, EPA Quality Staff, Office of Environmental Information, May 2000.

U.S. Environmental Protection Agency. Policy and Program Requirements for the Mandatory Agency-wide
    Quality System, EPA Order 5360.1 A2, EPA Quality Staff, Office of Environmental Information, May
    2000.

U.S. Environmental Protection Agency. EPA Guidance for Geospatial Data Quality Assurance Project
    Plans (Peer Review Draft),  (EPA QA/G-5G), EPA Quality Staff, Office of Environmental Information,
    2002.

U.S. Environmental Protection Agency. Business Rules for Latitude/Longitude Data Standard (Locational
    Data Standard), Office of Environmental Information, 2000.

Van Sickle, J., GPS for Land Surveyors, Ann Arbor Press, Second Edition, 2001.

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.
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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.
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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.
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                                     Appendix B

      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 were 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 as being a leaking storage tank at
a nearby factory.
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Portland,  Maine Quickly  Improves Infrastructure Management

Like many old cities, Portland had much old infrastructure data that were 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.
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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
     Hard Copy of Almanac
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Field Equipment, Continued
     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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                      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.
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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