LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Region 4 U.S. Environmental Protection Agency Laboratory Services and Applied Science Division Athens, Georgia Issuing Authority: LSASD Field Branch Chief Effective Date: May 5, 2020 Review Date: May 5, 2023 Purpose This document describes the Global Positioning System (GPS) and procedures, methods and considerations to be used and observed when using GPS to record location data in the field. Guidance is provided on accuracy requirements for various uses of location data and potential means to obtain the requisite accuracy. This document contains direction developed solely to provide internal guidance to LSASD employees. Scope/Application The procedures contained in this document are to be used by LSASD field investigators when using the Global Positioning System to obtain the geographical coordinates of sampling locations and/or measurements during field investigations. In LSASD investigations, GPS is the preferred means of collecting horizontal location information. In most cases the accuracy of GPS is unsuitable for collection of elevation data. On the occasion that LSASD field personnel determine that any of the procedures described in this section cannot be used to obtain the required coordinate information and alternate procedures are employed, the alternate procedure will be documented in the field log book, along with a description of the circumstances requiring its use. GPS users must be currently qualified as proficient in the operation of the specific GPS equipment to be used. The manufacturer's operation manuals should be used for detailed information on the use of specific GPS equipment. Mention of trade names or commercial products in this operating procedure does not constitute endorsement or recommendation for use. Page 1 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 TABLE OF CONTENTS Purpose 1 Scope/Application 1 1 General Information 3 1.1 Documentation/Verification 3 2 Methodology 3 2.1 General 3 2.1.1 GPS Description 3 2.1.2 GPS Accuracy Factors 4 2.1.3 Differential GPS 5 2.2 Requirements for Locational Information 6 2.2.1 Data Uses 6 2.2.2 Datums and Data formats 7 2.3 Quality Control Procedures 8 2.4 Special Considerations 8 2.4.1 Special considerations for the use of Trimble® Geo7X Mapping Grade Receivers 8 2.4.2 Special considerations for the use of Garmin® and other General-Use Grade Receivers 12 2.4.3 Use of Mobile Device GPS (cellphones/tablets) 13 2.4.4 Coordinate Conversion 13 2.5 Records 14 3 References 16 Page 2 of 18 Uncontrolled When Printed ------- Contents 1 General Information 1.1 Documentation/Verification This procedure was prepared by persons deemed technically competent by LSASD management, based on their knowledge, skills and abilities and has been tested in practice and reviewed in print by a subject matter expert. The official copy of this procedure resides on LSASD local area network (LAN). The Document Control Coordinator is responsible for ensuring the most recent version of the procedure is placed on the LAN and for maintaining records of review conducted prior to its issuance. 2 .Methodology 2.1 General 2.1.1 GPS Description The Navigation Satellite Time and Ranging (NAVSTAR) Global Positioning System (GPS) is a worldwide radio-navigation system created by the U. S. Department of Defense (DOD) to provide navigation, location, and timing information for military operations. System testing using a limited number of satellites began in 1978 with the system being declared fully operational in 1995. The system was declared available for civilian uses in the 1980s and has seen burgeoning civilian application for navigation and mapping. GPS is the U.S. implementation of a Global Navigation Satellite System (GNSS). Increasingly, GPS receivers have the capability to utilize signals from other GNSS such as the Russian GLONASS or European Galileo systems. LSASD has no limitations on the use of signals from other GNSS. The GPS system consists of three basic elements: the space segment, control segment, and user segment. The space segment consists of the constellation of up to 24 active NAVSTAR satellites in six orbital tracks. The satellites are not in geo-synchronous orbit, but are in constant motion relative to a ground user. The control segment consists of several ground stations that serve as uplinks to the satellites and that make adjustments to satellite orbits and clocks when necessary. The user segment consists of the GPS receiver which will typically consist of an antenna, multi- channel receiver, and processing unit. For the purposes of this document, the user segment GPS receivers may be loosely grouped into Recreational and Navigational receivers (henceforth referred to as General-Use receivers), Mapping Grade receivers, and Survey Grade receivers. GPS receivers derive positions by simultaneously measuring the distance (range) to three or more satellites in precisely known orbits and using trilateration of the ranges to calculate a unique position for the receiver. The range to each satellite is determined by precisely measuring the transit time of radio signals broadcast from the satellites. Page 3 of 18 LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 General-Use grade receivers are available on the retail market for a variety of applications including boating, hiking, and automotive navigation. They display an instantaneous reading of position and are generally not optimized for data collection. Waypoints containing instantaneous position fixes can often be stored and downloaded. The accuracy of these receivers is adequate for many environmental applications. Mobile Device (cellphone and tablet) GPS could fall in this category, but are commented on separately in the Special Considerations section. Mapping Grade receivers are used for applications such as resource management and Geographical Information System (GIS) feature collection. The receivers are capable of averaging multiple position fixes for greater accuracy and then data-logging the results with sufficient information to post-correct the positions as described below. The accuracy that can be achieved may be better than one meter. Survey Grade receivers can provide accuracy at the centimeter level by using long occupation times and special techniques for receiver use and data processing. Survey Grade receivers are not currently used by LSASD in field investigations. 2.1.2 GPS Accuracy Factors The accuracy of the basic GPS system is approximately 15m. GPS accuracy can be affected by a number of factors including the Selective Availability feature, atmospheric delays, satellite clock and orbit errors, multipath signals, signal strength, and satellite geometry relative to the user. In the early GPS implementation, the DOD used a feature known as Selective Availability (SA) to degrade the quality and subsequent accuracy of the GPS signals to non-DOD users. With Selective Availability enabled, the accuracy of position fixes could be as poor as 100m without the use of the differential correction techniques described below. Per an Presidential Executive order, the SA accuracy limitation has been disabled to enhance civilian GPS use. . As satellites move in their orbits and some signals are blocked by obstructions, the geometry of the available satellite signals relative to the user will constantly change. When the satellites with available signals are clustered closely together in the sky, small errors in range will result in large errors in reported position. Conversely, when the satellites are distributed more broadly across the sky, the resultant position errors will be at their minimum. The general measure of this phenomenon is Dilution of Precision (DOP), which may be represented as Position Dilution of Precision (PDOP), or more specifically for geographical coordinate collection, Horizontal Dilution of Precision (HDOP). Mapping and Survey Grade receivers generally can calculate and display DOP and allow the user to limit logging to times when the higher potential accuracy conditions of low DOP prevai 1. General-Use receivers may display DOP and use DOP with other factors to estimate a general accuracy figure. DOP may range from approximately 2 to 50, with high quality work usually requiring a HDOP of less than 4-6. Signal strength and multipath signals relate to the strength and quality of the signal reaching the receiver antenna. Signal attenuation by the atmosphere, buildings, and tree cover limit the accuracy of the ranges obtained. The measure of signal strength is Signal to Noise Ratio (SNR), Page 4 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 generally measured in decibels (db). Most receivers of any grade will display the SNR of the satellite signals in a bar graph or table. Mapping Grade Receivers generally allow the user to specify a minimum signal strength for the use of a satellite signal (commonly 2-15db). Poor signal strength can be resolved by waiting for satellite locations to change or moving the receiver location. Multipath signals result from portions of the satellite signal bouncing off terrain, structures, or atmospheric disturbances, resulting in a degraded total signal. Iligher quality Mapping Grade receivers may be capable of rejecting the stray multipath signals. Multipath may make it difficult or impossible to obtain accurate positions adjacent to buildings and an offset position may be need to be surveyed 2.1.3 Differential GPS Clock and orbital errors affect all GPS users, and atmospheric delays affect all users over a relatively wide region. A second GPS receiver in the same general area as the user will experience the same errors from these sources as the user's receiver. Consequently, correction factors from a remote station at a known location can be applied to the user's receiver in a process known as Differential GPS (DGPS). DGPS can be applied in real-time using additional radio signals, or after the collection event by a method called post-correction. An early real-time was the US Coast Guard (USCG) Nationwide Differential Global Positioning System (NDGPS), consisting of a network of 80 base stations supporting coastal and Mississippi river navigation via VI IF radio signals used to transmit the correction data. However, with the widespread utilization of WAAS in GPS receivers, the USCG is discontinuing the NDGPS, with all stations scheduled to be shut down by September 2020 The most common real-time DGPS are Space Based Augmentation Systems (SBAS). The most common SB AS used in the United States is the Wide Area Augmentation System (WAAS), developed by the Federal Aviation Administration to meet the additional demands on GPS for aircraft navigation. The W AAS network of base stations collects information on satellite clock errors, orbital errors, and atmospheric conditions. The error information is transferred to satellites in geo-synchronous orbits arid subsequently broadcast to suitably equipped GPS receivers on frequencies compatible with the GPS range signals. Almost all current GPS receivers are capable of utilizing WAAS for differential correction. Note: LSASD has received G arm in receivers have been noted to ship with WAAS turned off. In order to utilize WAAS on new receivers, it must be enabled in the setup menu Mapping grade GPS receivers are capable of increased accuracy beyond the capabilities of WAAS by a method called post correction. Post-Corrected DGPS is accomplished by downloading the receiver survey files to a desktop or laptop computer and then retrieving correction files for the same time period (generally via the internet) from an established base station in the area of the survey. Post correction base stations, called Continuously Operating Reference Stations (CORS) are managed by the National Oceanographic and Atmospheric Agency (NOAA). There are other post correction base stations operated by universities, municipalities, and private industry. Post- processed accuracy improves with proximity of the base station to the surveyed locations and base station data should be used from a station within 300km of the site surveyed and ideally within 75km. The use of multiple base stations will improve accuracy. The survey positions are Page 5 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 processed by application software and a new set of positions is generated using the correction data. The capability for post-processed differential correction is limited to Mapping Grade and Survey Grade receivers. Various factors limit GPS accuracy in the vertical plane to approximately half of that obtainable in the horizontal plane, i.e., if a location fix is accurate to 3 m in the horizontal plane, it may only be accurate to 6 m in the vertical plane. Since relatively high accuracy is generally required for utilization of elevation data, GPS is rarely used to obtain and report elevations. 2.2 Requirements for Locations! Information 2.2.1 Data Uses Locational information can serve many purposes in an environmental investigation, a few of which are listed below: • Providing an unambiguous means to identify facilities or sampling plats. • Providing locational information to key analytical data in a GiS based data archiving system to the original sampling locations. • Differentiating watersheds. • Providing information to calculate extents and volumes of contamination. • Providing a means to relocate the media represented by samples for removal or treatment. • Providing information to prepare presentation graphics of sampling locations. Depending on the specific uses for the data and the type of work being performed, there will be different needs for the accuracy of the locational data. Studies where a sample represents a large area of relatively homogeneous material would not requi re the same accuracy as the location of a permanent monitoring well. Below are broad guidelines for the accuracy that might be required for different applications. Desired Accuracy Application 100-20 m Open ocean work where sample is presumed to be representative of a large area 20 in Open water work (lakes or estuaries) where sample is presumed to be representative of a large area 10 m Stream and river work where samples are presumed to be broadly representative of a reach 5-3 m Stream work where samples arc representative of a specific narrowly defined section 10m Air Monitoring Stations 10-3 m Microscale air monitoring Page 6 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 3 - 1 m Permanent monitoring wells 1 m Locations of 'Hot Spots' destined for removal of limited arcal extent 3 - 1 m Locations of Temporary groundwater wells in plumes requiring narrow delineation 3 m Locations of Temporary groundwater wells in broad plumes 3 m Locations of environmental samples with sample spacing >20 m 5m Locations of environmental samples with sample spacing >60 m 200 - 20 m Coordinates describing a facility where mobile waste units are sampled 30 - 3 m Locations of industrial process areas orNPDES permitted facilities where the sampling locations arc described in field notes relative to the process or site features Specific demands of a study may drive increased or decreased requirements for accuracy. The preferred means of location al data collection for most studies will be GPS, although alternate means are permissible if they meet accuracy requirements. The following table indicates the accuracy that may be expected from various means of establishing coordinates. Accuracy Description 200 - 50 m Map Derived, coarse work 40 - 20 m Map Derived, fine work or using GIS with digital imagery 15 m General-Use Grade GPS, w/o WAAS 5 m General-Use Grade GPS, w/ WAAS or beacon corrections 10 m Mapping Grade GPS, no corrections, averaged readings. 3 m Mapping Grade GPS w/ differential correction, averaged readings 1 m Mapping Grade GPS w/ differential correction, controlled DOP and SNR, averaged readings < 10 cm Sun-eying Grade GPS or optical surveying (dependent on baseline length) Accuracy is a term used to describe the degree of conformity of a measurement. In GPS, accuracy is usually specified as an estimate of the radius from the measured coordinates that is likely to include the actual coordinates. The estimate will be based on a percentage likelihood or a certain number of standard deviations that the accuracy estimate is met. As such, it is recognized that some measurements will fall outside of the specified accuracy. For the purposes of LSASD GPS work, the nominal accuracy figures derived from manufacturer's literature for specific operating conditions, displayed by the receiver at the time of feature collection, or output from processing software will be taken at face value. 2.2.2 Datums and Data formats In general, a datum is a reference from which other measurements are taken. In the development of surveying systems by civil entities, different datums were used as base references that will result in differing coordinates for the same location. A GPS receiver will generally display coordinates in a number of different user-selected datums. Unless there are specific requirements on a Page 7 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 project, all LSASD work should be conducted using the WGS84 datum. Alternatively, the nearly equivalent NAD83 datum may be used if WGS84 is unavailable as a receiver option. If an alternate coordinate system is used where coordinates are obtained and recorded in field logbooks, the use of the alternate coordinate system should also be noted in the logbook. The Region 4 EQuIS database requires that coordinates for sample locations be entered in the WGS84 datum and dd.dddddd format. Unless specific project requirements dictate otherwise, all coordinates explicitly stated in reports will be in WGS84 format and in all cases the datum used will be specified. There is no LSASD policy on significant digits for GPS information, and accuracy should not be implied from the presence of significant digits in reported coordinates. However, good scientific practice should be followed in the presentation of locational information in order that useful information not be truncated or a higher degree of accuracy implied. The following table shows the incremental distance in latitude represented by the least significant digit for vanous coordinate formats: dd.dddddd0 Approximately 4" or 10 cm dd.ddddd0 Approximately 44" or 1.1 m dd.dddd0 Approximately 36' or 11 m ddPram'ss" Approximately 100' or 30 m dd°inin'ss.x" Approximately 10' or 3 m dd°mm'ss.xx" Approximately 1' or 30 cm dd^nm.xxxx1 Approximately 7" or 18 cm dd°mm.xxx' Approximately 6' or 1.8 m dd^iini.xx1 Approximately 60' or 18 m 2.3 Quality Control Procedures By nature of its origin in the 1)01) and recent application to aircraft navigation, the GPS is designed for high reliability. GPS failures resulting in an incorrect reading beyond the bounds of known errors are so rare that the possibility can be ignored for most LSASD studies. If a study requires the verification of receiver function, this can be accomplished by verifying that a receiver displays the correct position while occupying a known benchmark. 2.4 Special Considerations The data quality objectives for the application, availability of receivers, and other factors will dictate the type of receiver used. There are several specific considerations for the use of the various GPS receivers available at LSASD. 2.4.1 Special considerations for the use of Trimble© Geo7\ Mapping Grade Receiv ers Page 8 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Several important settings can be adjusted or checked under the 'Setup" toolbar. Suggested settings for Trimble® Geo7X receivers are: 2.4.1.1 Settings -Coordinate System: System = Latitude/Longitude Datum = WGS 1984 Altitude Reference = MSL Altitude Units - Feet These settings would rarely need to be changed, but should be checked prior to collecting data. 2.4.1.2 Settings Real-time Settings Set to: Choice 1 = Integrated SBAS Choice 2 = Wait for Real-time When 'Choice T is set to 'Wait for Real-time", the receiver will not log positions if a WAAS signal cannot be received. When this occurs, 'Choice 2' may need to be changed temporarily to 'Use uncorrected GNSS'. The location would then be logged with the reduced accuracy of uncorrected GPS, which should be noted in field logbooks. The accuracy of the position can be improved later by post-processing. 2.4.1.3 Settings -Logging Settings At the top of the logging settings dialog is the 'Accuracy Settings' label. Tap the 'wrench' box to the right of the first field to open the Accuracy Settings dialog box. Set the first box under 'Accuracy Value for Display/Logging' to 'Horizontal' The box below the Horizontal/Vertical selection chooses whether positions will be corrected in real time or by post-processing. Choose 'In the field' if Real-time WAAS corrections will be used, or ' Postprocessed" if positions will be post-corrected. This selection will affect the accuracy estimates displayed. If Real-time correction is used when this setting is set to 'Postprocessed', the estimated error reported will be erroneously low. Select 'Yes' or 'No' for accuracy based logging. Selecting 'Yes' will prevent the receiver from logging until the desired accuracy can be achieved. This setting is recommended when a specific accuracy for locational data is required. Selecting 'Yes" enables the following choices: The next box, 'Apply Accuracy-based Logging to:' can be set to point features or 'All Features'. Set appropriately. Page 9 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 The 'Required Accuracy' field selects the accuracy threshold that will allow logging. If a position cannot be logged because the threshold cannot be met, several options are available: • Set the accuracy threshold to a higher but still acceptable value. • Plan to post-correct the coordinates and change the settings in this dialog accordingly. • Post-correction will generally allow more accurate correction than WAAS. • Return to the point at a later time when propagation or satellite geometry is more suitable. • Use the 'Offset' feature (see below) to log the positions from a more suitable location (e.g. less tree cover). The screen shot below shows the Accuracy Settings Dialog Box: Page 10 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Tcrrrfync f Setup 0 < y Accuracy Settings 4;U Accuracy /a!uŁ For Disp o // I OQtlififl /¦ ( ( I t f -* I J - f -.1 Oi f" I !/ • I > I 1 f\ I U w / WU ^ . V ^ 'J ' i ' ^ .J Apply Accuracybas&d Logyir^ ro Squired Accuracy rZ /• Done ) E3J ] Cancel Page 11 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 If the point to be logged cannot be occupied, or signals cannot be received at the location, the 'Offset' feature of the receiver can be used. The I.SASD Geo7X receivers can employ a laser rangefinder, compass, and inclinometer to calculate the offsets. To use the 'Offset' feature: 1. Begin logging from the offset location. 2. Pull down the 'Options' menu and select 'Offset', then 'Distance - Bearing' 3. The Offset dialog will open where distances and bearings could be manually entered. 4. To use the laser rangefinder and compass to populate the dialog fields, press the physical' 1 1 button located on the receiver below the screen. 5. The laser rangefinder application will start and a red sighting laser will turn on. Point the laser at the desired point to survey and sight the object in the crosshairs on the screen. When sighted on the survey object, tap on the ' o • icon on the screen to lock in the distance and bearing at the bottom of the screen. Press the '-o-' icon again to update the readings, or press the ly/ icon to transfer the bearing and distance to the Offset dialog box. 6. If the numbers transferred to the Offset dialog box are appropriate, tap 'Done' to return to the feature logging screen. There is no quality system calibration performed on the electronic compass, inclinometer, and rangefinder. It is the responsibility of the user to assure that the bearings and ranges returned by the laser rangefinder system will result in accuracy consistent with the overall GPS work. A quick check for reasonableness can be performed by comparing the logged position on the Map screen with the current position shown. Photos can also be taken with the unit and associated with the logged features. The user is referred to vendor documentation for instruction in the use of this feature. Trimble® receivers at LSASD have been loaded with a data dictionary that can facilitate the management of GIS data. If the COC G1S dictionary is selected at the time of file creation, LSASD standard media codes can be assigned to features at the time of logging that will accompany the data through the download process. The use of the COC__GIS data dictionary can simplify the management of the data when processed in a GIS system or when submitted to the EQuIS data archiving system. The logging interv al of the Trimble® Geo 7X receivers can be set to a 1 or 5 second interval as an option during feature collection. The setting may be set to 1 second to expedite feature collection. A point feature should have a minimum of 36 positions logged to obtain the additional accuracy afforded by the averaging of positions. After a minimum of 36 positions are logged and the feature is closed, the averaged coordinates for the location can be obtained by selecting the feature on the 'Map' screen. The averaged position should always be the one entered into field notebooks. 2.4.2 Special considerations for the use of Garmin® and other General-Use Grade Receivers Several types of General-Use grade of receivers are in use at LSASD, with many from the Garmin® product line. Most of the Garmin® receivers operate with a similar interface to facilitate use of the various devices. The nautical receivers/depth sounders are suitable for recording location data within the limitations described for the General-Use grade receivers. Page 12 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Some receivers will allow averaging of positions to improve accuracy. Use of this feature is recommended when possible. Anecdotal experience at LSASD suggests that GPS designed primarily for automobile navigation is unsuitable for obtaining locational data. Many Garni in receivers will display on the status screen whether WAAS differential correction is in use by displaying small 'D' characters at the base of the signal strength bars. Some newer receivers do not display this information directly and correction status can only be inferred by the accuracy estimates or by monitoring the status screen for acquisition of signals from the WAAS satellites. As noted previously, WAAS is disabled as the default setting in new Garni in GPS units, therefore WAAS must be enabled in the Settings Menu to achieve real-time differential correction 2.4.3 Use of Mobile Device GPS (cellphones/tablets) A variety of applications on cellphones and tablets can access GPS features of the devices. The applications are generally not optimized for data collection and estimations of accuracy, when present, can be non-rigorous. It is generally recommended that locational data not be collected with these devices. If they are used, the locations should be viewed against aerial imagery to verify credibility and when submitted to the EQuIS data system the accuracy verification code of 'Cell/tablet GPS' should be used. The same would appl y if automotive-specific GPS were used. 2.4.4 Coordinate Conversion Coordinates may be displayed in different formats on the various receivers, or coordinates obtained from outside LSASD may be presented in a format other than that required. If the coordinates are in the correct datum, but recorded in the dd°mm'ss.sss" format they can be arithmetically converted to dd.dddddd format. Convert to decimal degrees as follows: Converting to decimal degrees (dd.dddddd) from degrees°minutes'seconds" (dd°mm'ss.sss"): dd.dddddd = dd + (mm/60) + (ss.sss/3600) Example: Convert 33°28'45.241" to decimal degrees 33 + (28/60) + (45.241/3600) = 33.479236 The reverse conversion is accomplished as follows: Converting to degrees°minutes'seconds" from decimal degrees Starting with dd.dddddd Multiply .dddddd by 60 to obtain mm.mmmm Page 13 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Multiply .mmmm by 60 to obtain ss.sss Then dd°mm'ss.sss" = dd & mm & ss.sss Example: Convert 33.479236 to dd°mm'ss.sss" format Multiply .479236 by 60 to obtain 28.7540 (mm.mmmm) Multiply .7540 by 60 to obtain 45.241 (ss.sss) Dd°mm'ss.sss" = 33° & 28' & 45.241" = 33°28'45.241" The standard format for navigational purposes is decimal minutes (dd mm.mmm") This format is utilized due to the fact that nautical navigation charts are set up in this format. However, location information must be converted to a decimal degree (dd.ddddd0) format in order for G1S software to properly interpret the information and for submission to the Region 4 EQuIS database. Assuming the coordinates have been recorded in the proper datum, the conversion can be accomplished by dividing the minutes portion of the coordinates by 60. Converting to decimal degrees from decimal minutes: dd.ddddd0 = dd + (mm.mmm/60) Example: Convert 81°49.386' to decimal degrees 81 + (49.386/60) = 81.8231 degrees The reverse conversion is accomplished as follows: dd°mm.mmm' dd & (,ddddd*60) Example: Convert 8 1.823 1 degrees to decimal minutes (dd'mm.mmm') Multiply .8231 by 60 to obtain 49.386 (mm.mmm) 81° & 49.386' = 81°49.386' GPS users should familiarize themselves with the differences between the formats, as they can appear similar. Spreadsheets can automate the conversion process. 2.5 Records The GPS coordinates and the I .S ASI) equipment identification number of the GPS receiver should be recorded in field logbooks at the time of GPS coordinate collection. The data logging capability of Page 14 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 receivers may be used in lieu of the requirement to record the coordinates in logbooks when the following conditions can be met: • The location can easily be found later if it needs to be resurveyed prior to demobilization. A permanent monitoring well can easily be resurveyed, while most open-water work would not afford this opportunity. • The data is downloaded and ascertained to meet the accuracy requirements for the project prior to demobilization from the site. • The data is stored in at least two separate locations for transport, such as a laptop hard drive and flash drive or compact disc. In all cases where positions are electronically recorded, the provisions of the Electronic Records section of the LSASD Operating Procedure for Control of Records (LSASDPROC-002) should be followed. Where locational data is collected and processed electronically, but not reported explicitly in the final report, a copy of the coordinates in text format should be output and entered into the proj ect tile in paper or electronic form. The output should include: • Latitude, generally in dd.dddddd format. • Longitude, generally in dd.dddddd format. • Date of collection. A note on the differential correction process used where it supports the accuracy requirements. • The datum used for the export. Trimble® Pathfinder Office can create files with this information when exporting coordinates to a text file. The information will be contained in the ,pos and ,inf files. Page 15 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 3 References Rand Corporation, The Global Positioning System. Assessing National Policies. Appendix B. GPS History. Chronology, and Budgets. 1995. LSASD Operating Procedure for Control of Records, LSASDPROC-002, Most Recent Version. Trimble© Navigation Limited, Mapping Systems General Reference. Revision B, 1996. USE PA, Global Position Systems - Technical Implementation Guidance. Office of Environmental Information (EPA/250/R-03/001), 2003. USEPA, CilS Technical Memorandum 3. Global Positioning Systems - Technology and It's Application in Environmental Programs. Research and Development (PM-225). EPA/600/R-92/036, 1992. USEPA, Locational Data Policy. Office of Information Resources Management, 1RM Policy Manual 2100 Chapter 13, 1991. Page 16 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Revision History The top row of this table shows the most recent changes to this controlled document. For previous revision history information, archived versions of this document are maintained by the LSASD Document Control Coordinator on the LSASD local area network (LAN). LSASDPROC-110-R5, Global Positioning System, replaces SESDPROC-110-R4 General: Updated format and naming convention due to agency realignment and new Division/Branch names. Special Considerations: Section added related to the use of mobile device GPS for data collection. May 5, 2020 SESDPROC-110-R4, Global Positioning System, replaces SESDPROC-110-R3 Cover Page: LSASD's reorganization was reflected in the authorization section by making John Deatrick the Chief of the Field Services Branch. The FQM was changed from Liza Montalvo to Hunter Johnson. Revision History: Changes were made to reflect the current practice of only including the most recent changes in the revision history. Section 2.1.1: Changes were added to elaborate on the description and purpose of GPS systems. Section 2.1.3: Changes made to reflect the abilities of different differential GPS systems. Sentence added to reflect the preferences to certain differential GPS systems. Section 2.2.1: Added to explain that the GPS measurement estimate will be based on a certain number of standard deviations. Section 2.2.2: Changes were made to reflect a name change. Section 2.4.1: Changes were made to reflect the current procedures. Section 2.4.2: Changes were added to reflect the changes in current procedure practices. Conversion process removed and revised in a later section. Section 4.X: Conversion procedure updated and revised to reflect the current practices. Paragraph added to reflect the standard format for navigational purposes. June 23, 2015 Page 17 of 18 Uncontrolled When Printed ------- LSASDPROC-110-R5 Global Positioning System Effective Date: May 5, 2020 Section 2.5: Removed the DOP where it includes accuracy requirements for what the output should include to reflect the changes in the operating procedures SESDPROC-110-R3, Global Positioning System, replaces SESDPROC-110-R2 April 20, 2011 SESDPROC-'l 10-R2, Global Positioning System, replaces SESDPROC-110-R01 November 1, 2007 SESDPROC-110-R1, Global Positioning System, replaces SESDPROC-'l 10-R0 October 1, 2007 SESDPROC-110-R0, Global Positioning System, Original Issue March 22, 2007 Page 18 of 18 Uncontrolled When Printed ------- |