remote sensing tools assist in environmental forensics:part ii—digital tools

Environmental Forensics (2001) 2, 223±229

doi:10.1006/enfo.2000.0033, available online at http://www.idealibrary.com on

Remote Sensing Tools Assist in Environmental Forensics:Part IIÐDigital Tools

G. M. Brilis

National Exposure Research Laboratory, U.S. Environmental Protection Agency, P.O. Box 93478, Las Vegas, NV89193-3478, U.S.A.

R. J. van Waasbergen

Applied Environmental Data Services, 2206 Franklin Road, Arlington, TX 76011, U.S.A.

P. M. Stokely

Environmental Protection Agency, Region 3, 12201 Sunrise Valley Drive, 555 National Center, Reston, VA 20192,U.S.A.

C. L. Gerlach

Lockheed Martin Corporation, 980 Kelly Johnson Drive, Las Vegas, NV 89119, U.S.A.

(Received 8 September 2000, Revised manuscript accepted 29 November 2000, Published electronically 14 February 2001)

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This is the second part of a two-part discussion, in which we will provide an overview of the use of GIS and GPS inenvironmental analysis and enforcement. Geographic Information Systems (GIS) describes a system which manages,analyses and displays geographic information. Environmental applications include analysis of source, extent andtransport of contaminants, nonpoint runo� modeling, ¯ood control, and emergency response support. The ability toexamine spatial relationships between environmental observations and other mapped and historical information, and tocommunicate these relationships to others, makes GIS valuable in environmental forensics. The US EnvironmentalProtection Agency currently requires the inclusion of locational information with all other environmental data that iscollected. Geographic Information Systems is a complex tool that requires careful planning and design to be successfullyimplemented. Choices in hardware, software and data development must be based on evaluation of project objectives,analytical requirements, data availability and data development considerations. Data sets must be evaluated anddocumented with metadata. The Global Positioning System (GPS) is a satellite-based system which provides highlyaccurate, three-dimensional position information anywhere on the earth's surface. Using portable radio receivers, ®eldanalysts can easily record the positions of spill sites, sampling locations and other environmental features. Spatialaccuracy of GPS ranges from 20±30 m (single receiver) to 1±5 m (di�erential GPS) for navigation-grade instruments,and down to millimeter level accuracy for geodetic units. Global Position Systems can be used not only to capturespatial information into a GIS system, but also to evaluate and quantify the spatial accuracy of existing digital mapdata, and to provide control points for existing aerial photographs and other remotely-sensed data. # 2001 AEHS

Introduction

Part I of this two-part series discussed the applicationof traditional remote sensing techniques in environ-mental forensics (Brilis, Gerlach and van Waasbergen,2000). The traditional techniques focused on mappingand aerial photography. Prior to the introduction ofcomputers, aerial photographs were acquired, pro-cessed, and interpreted manually and/or by mechanicaldevices. Application of maps and aerial photographyhas been a valuable tool for environmental forensics.The introduction and proliferation of computers in the®eld of remote sensing, in addition to satellites, haschanged the way data is acquired, processed, andanalysed. A more in-depth look at aerial photographyis described by Grip, Grip and Morrison (2000).

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The use of Geographic Information Systems (GIS)as a tool in environmental forensics is increasing.Geographic Information Systems are systems wheregeographic data describing features on the earth'ssurface are managed, displayed, manipulated, andanalysed (USEPA, 1992a). Digital remote sensing andthe use of GIS make it possible to rapidly collect andanalyse spatial data, yielding a powerful set of tools forthe analysis of the source, extent, and transport ofvarious types of contamination.

The ability to analyse complex, spatial data makesGIS technology interesting to a growing number ofusers within the environmental sciences community.Applications include environmental monitoring andanalysis, modeling nonpoint runo�, landscape ecology,¯ood control modeling, enforcement actions, and

# 2001 AEHS

224 G.M. Brilis et al.

emergency response support. The U.S. EnvironmentalProtection Agency (EPA) is tapping into the manycapabilities of GIS technology as it continues its long-term evaluation of ecological trends.

Recognizing the critical role of geographic data,EPA created the Locational Data Policy (LDP) in1991. This policy establishes the principles for collect-ing and documenting latitude/longitude coordinatesfor facilities, sites and monitoring and observationpoints regulated or tracked under Federal environmen-tal programs within the jurisdiction of the EPA. Theintent of the LDP is to extend environmental analysesand allow data to be integrated based upon location,thereby promoting the enhanced use of EPA's exten-sive data resources for cross-media environmentalanalyses and management decisions. This policyunderscores EPA's commitment to establishing thedata infrastructure necessary to enable data sharingand secondary data use. The EPA accuracy goal hasbeen established at 25 m and the best method currentlyavailable to satisfy the requirements of LDP iscurrently considered to be GPS (Geospatial Metadata,1997). Since the ®nalization of LDP, technology hasenabled a 2±5-m accuracy using simple hand-helddevices and di�erential error-correction, and sub-meteraccuracy with more sensitive units.

The heavy emphasis on analytical manipulation ofspatial data is the main characteristic that distinguishesGIS from other technologies like computer-aideddesign and electronic mapping systems. Using GIS, aforensic scientist is able to present a complete picture ofa site location, tiering maps of streams, geopoliticalboundaries, transportation routes, topography, andexamine the spatial relationships between them. Inaddition, GIS display tools allow these relationships tobe communicated to others in a meaningful way.

Geographic Information Systems are used toorganize ®eld data in a spatial context that can allowdecision makers to make more informed choices as thestudy progresses. There is a growing need for spatialanalysis to be an integral part of routine data analysisand decision-making. To meet this need, GIS technol-ogy is migrating to the desktops of applied technol-ogists in ®elds like biology, economics, andenvironmental science.

The current trend is to combine GIS technology withInternet applications to build distributed spatial data-bases and to provide GIS tools to users anywhere in anorganization, or even in the ®eld. Distributed spatialdatabases can be more reliably maintained, becauseeach contributor can focus on the data sets with whichthey have the most expertise. Development of uniformstandards for spatial data formats and quality will makeit possible for GIS users to more con®dently drawon data sets that are built and maintained by others,without a need to acquire, convert and maintain itthemselves.

Technique and Scope

The power of GIS to generate highly specializedinformational maps makes it an e�ective method forpresenting information to decision makers, the public,and potentially in the courtroom. But GIS is capable ofmuch more than generating maps and presenting data.

Environmental forensic studies can produce complexdata that are di�cult to represent verbally or some-times even visually. Using GIS, forensic investigatorsare able to interpret spatial data, manage complexdatabases, and use layers of information from varioussources. Based on GIS, investigators can produce arealistic and understandable visual analysis of a case.Some common analysis capabilities include measure-ments (spatial extent and volumes of mapped features),attribute reclassi®cation (combining information fromdi�erent data layers to determine, for example, the soiltypes in land parcels owned by di�erent people),topological overlay (to determine common boundariesor subdivide existing map units based on features inother layers), connectivity operations (to determine theshortest route along a network, for example),coordinate transformations (to bring di�erent datasets into a common spatial coordinate system so theycan be overlain), and surface analysis.

One example of how GIS analyses were used inenvironmental forensics was a case in which EPAassessed a number of mining companies for environ-mental damages that resulted from lead-zinc mining insouthwestern Missouri. Site investigations and photointerpretation were used to map the distribution andextent of hazardous mine waste. This was combinedwith historic lease and ownership information todetermine the extent to which each company shouldbe held liable for cleanup. In one instance, theallocation was further re®ned by the use of historic airphotos: by measuring changes in extent and volume ofmine tailings on air photos over several years, theamounts of waste produced during the stewardship of aspeci®c company could be determined. This allowed thecost allocation for that company to be adjusted to moreaccurately re¯ect their contribution to the problem.

Another application is used to support Section 404 ofthe Clean Water Act (CWA) enforcement investiga-tions. Section 404 outlines the procedures and require-ments for obtaining federal permits prior to thedischarge of dredged or ®ll material into Waters ofthe United States including wetland areas. Theseinvestigations utilize the interpretation of historicaland current aerial photography to document the loca-tions of historical wetland areas relative to current siteconditions. Aerial photography is obtained, scannedand geo-referenced to a known coordinate system usingDigital Ortho Quarter Quadrangles (DOQQs) pro-duced by the United States Geological Survey. DigitalOrtho Quarter Quadrangles are map accurate images inwhich every pixel, or picture element, has a knowncoordinate value. Through the geo-referencing process,these coordinate values are transferred to the historicalaerial photography. Once all the aerial photography isprojected in the same coordinate system then features orconditions observed on one date can be easily trans-ferred and overlayed on each date of photography.

This procedure enables historical wetland bound-aries to be transferred to current aerial photographywhich dramatically showed in one recent case: residen-tial roads, lots, and storm water lakes located in formerwetland areas. The picture this presented was in¯uen-tial in convincing the jury that wetlands had been ®lledwithout a permit. The dramatic presentation of ``beforeand after'' aerial photography coupled with the ability

Remote Sensing Tools Assist in Environmental Forensics 225

to accurately geo-reference and overlay features ofinterest provides strong visual evidence of changes on asite over time. This technique has been used success-fully on a number of enforcement investigations acrossEPA Regions.

Planning a GIS Project

Planning is an important step in a forensic investiga-tion. Geographic Information Systems is a complextool that requires planning in many areas to avoidproblems that can a�ect the project's outcome.Scientists have identi®ed six areas essential to theGIS project planning life cycle. They are to de®neproject objectives, identify analytical requirements,de®ne data and hardware requirements, determinedata availability, resolve data development issues andimplement project plans.

As with any analytical process, the quality of theresult is dependent upon the recognition of the exactproblem and the implementation of the correct steps inaddressing it.

Project Objectives

De®ning speci®c project objectives reduces wasted timeand e�ort in the project planning life cycle. Projectobjectives should encompass every aspect of the project,from data collection and manipulation to data displayand archival storage. Not all aspects of a project areknown in their entirety at the onset of a project, ofcourse, so project objectives should be ¯exible enoughto be customized as more knowledge related to thestudy becomes available. Sometimes very little is knownabout the project at the beginning of the study and apreplanning data gathering e�ort is necessary toestablish the facts.

Analytical Requirements

The next step in planning is the identi®cation of analy-tical requirements. The de®ned analytical requirementwill be used to specify more exact standards for data-base data quality, resolution, and scale. This stage ofthe GIS planning process requires the input of projectsta� and GIS specialists. It is important that the projectsta� communicate their exact needs to the GIS experts.After the requirements are established, program man-agement sta� should prioritize the needs and establishmeasurable data quality objectives to meet them.

At this stage it is useful to consider the attributeinformation required for analysis, minimum dataresolution and scale, and data input and outputformats. Data visualization is a�ected by the sensitivityand resolution of graphics terminals and printers.

Data Availability

The project's analysis objectives can only be met if thedata are available. The degree to which GIS data areavailable is related to the resolution, scale, andcompilation date required by the study. Anotheravailability factor is cost. Data may be available inthe sense of existing but may be beyond the costrestrictions of the particular project. The data needed

for a project will fall into one of three categories: datathat already exists and is available at no cost or mayeven be supplied with the GIS software; data that mustbe purchased from a vendor; and data generatedspeci®cally for the project at hand.

Data Development Issues

Data development may be required to address the dataquality objectives of the project. At this point, datamust be assessed to ascertain their adequacy. Projectdeadlines and data quality objectives (DQOs) shouldbe reviewed at this time. The personnel responsible forcritical decisions should be involved in this adequacyreview. Key questions should be asked. Are the dataadequate to meet the DQOs of the project? Candefensible decisions be made based on the data athand? Is the data quality su�cient? Is there enoughtime to gather additional data if necessary?

In any one project, there are generally three types ofspatial data sets:

(1) Contextual data. These are used on maps primarilyto provide a common reference, but are not usedfor analysis or modeling. Examples of contextualdata include state and county boundaries, oil®eldboundaries, major highways or other landmarks.Most often, this is data that may be supplied by aGIS software vendor.

(2) Relevant basemap data. These are commonlyobtainable data sets that may be relevant to theenvironmental issues and may be used for analysisor modeling. Examples include topography, streetnetworks, hydrography, soil and land-use data,known sewage outfalls, and historical air photos.Typically, this is data that must be purchased froma vendor.

(3) Speci®c project data. These are the data that areunique to the project at hand, and may includesampling locations, results of site investigations,monitoring well data, new air photos, and facilityplans. At the beginning of a project, this will be thedata generated speci®cally for the project at hand.

Of these three categories, the contextual data areusually the easiest to obtain, and has the fewest qualityrequirements. The basemap data are often also easy toobtain, but great care must be taken to ascertain thequality of these data sets, and to understand the limitsof their use in spatial analyses or modeling. Speci®cproject data are generally the category over which onehas the most control, but which also require the moste�ort and careful planning to obtain.

Digitized data and the informational maps thatresult from GIS applications are only as reliable as thequality of the data that is input. Whenever GIS is usedfor decision-making, it is important to state thecon®dence levels of the information. Some researche�ort is under way to represent the reliability of thedata by subtle di�erences in the display characteristics.

All aspects of the information should be evaluatedfor cost impact. Cost considerations may include theacquisition of data, travel costs, quality assurance,contractor fees, and all project management costs.


Metadata

Metadata is data about data and consists of informa-tion that characterizes data. Metadata are used toprovide documentation for data products. In essence,metadata answer who, what, when, where, why, andhow about every facet of the data that are beingdocumented. For remote sensing tools, metadataincludes (Geospatial Metadata, 1997):

Identi®cation information

Basic information about the data set. Examples includetitle, geographic area covered, currentness, and rulesfor acquiring or using the data.

Data quality information

An assessment of the quality of the data set. Examplesinclude positional and attribute accuracy, complete-ness, consistency, sources of information, and methodsused to produce the data.

Spatial data organization information

Describes the mechanism used to represent spatialinformation in the data set. Examples include themethod used to represent spatial positions directly(such as raster or vector) and indirectly (such as streetaddresses or county codes) and the number of spatialobjects in the data set.

Spatial reference information

A description of the reference frame for, and means ofencoding, coordinates in the data set. Examples includethe names of and parameters for map projections orgrid coordinate systems, horizontal and verticaldatums, and the coordinate system resolution.

Entity and attribute information

Describes information about the content of the dataset, including the entity types and their attributes andthe domains from which attribute values may beassigned. Examples include the names and de®nitionsof features, attributes, and attribute values.

Distribution information

O�ers information about obtaining the data set.Examples include a contact for the distributor,available formats, information about how to obtaindata sets online or on physical media (such as cartridgetape or CD-ROM), and fees for the data.

Metadata reference information

This provides information on the currentness ofthe metadata information and the responsible party.The standard has sections that specify contact informa-tion for organizations or individuals that developedor distribute the data set, temporal information fortime periods covered by the data set, and citation

information for the data set and information sourcesfrom which the data were derived.

The standard for how metadata information isorganized in a computer system or in a data transfer,or by which this information is transmitted or commun-icated to the user are not yet de®ned. Additionalinformation about metadata is available from theFederal Geographic Data Committee (FGDC) http://www.fgdc.gov

Implementation

The GIS project implementation phase carries out thedatabase development and analysis objectives. Thedatabase design de®nes the database structure, itscharacteristics, coverage attribute coding scheme, datamodels, and automation methods. The resulting designdocument should determine if the GIS database meetsthe project's analytical objectives. The data captureand automation phase carries out the database designthrough data acquisition and integration of data intothe GIS system. The database design includes digitizinganalog maps, converting digital data into GIS format,and correcting and coding data.

Once the database is complete, the GIS analysisfunctions are tested. When the sta� are satis®ed withthe system's ability to meet the analytical requirementsof the project, database production can begin.

GIS User Interface

Geographical Information Systems rely on a relationaldatabase management system to provide the ability toquery, manipulate, and extract geographic referenceand attribute data. This approach permits standardstatistical manipulations of attribute data, as well aslogical and boolean queries based on GIS featurecharacteristics (USEPA, 1992a). Most GIS softwarepackages provide a generic tool set to perform spatialanalysis operations, database operations, data manage-ment tasks, and data reporting/mapmaking tasks. Thegeneric tools can then be modi®ed to suit the needs ofthe organization, group, or individual user. Suchcustom GIS applications can be built to simplifycomplex tasks, automate data capture and data entry,and provide decision support tools to novice users.Automation and data-validation save time and canprevent many errors.

Geographic Information Systems And RemoteSensing

Remote sensing data, from vegetation and climatic data tooutlines of manmade structures, can form much of theinformation that is entered into a GIS. The technologies ofremote sensing and GIS are distinct, but complimentary.Di�erent equipment and technical skills are needed foreach, but in both cases the user must have a string grasp onthe information that is collected, be it forestry, geology,man-made structures, etc. Remote sensing technologyfocuses on sensor systems and image processing, whereasGIS requires expertise with the principles of spatialanalysis, map projections and databases. (Arono�, 1995)

Geographic Information Systems and remote sensingare both used in environmental forensics. Remote


sensing analyses are supported by other data stored ina GIS, and GIS applications will be improved byremotely sensed data. The availability of informationthat only remote sensing can provide, combined withthe powerful tool and technology of GIS, enable aforensic scientist to more e�ciently and e�ectivelyconduct an environmental investigation.

Global Positioning System Technology

Global positioning system (GPS) technology is asatellite-based radio positioning and time-transfersystem that can provide accurate, three-dimensionalgeographic positioning anywhere on the earth'ssurface. Developed by the U.S. Department ofDefense, this technology was designed primarily formilitary navigational systems, but there are numerousgeocoding applications in the ®eld of environmentalscience. Global Positioning Systems has become astandard technology in geodesy, geography, surveying,and environmental monitoring and analysis.

The Science of Satellite Positioning

By using radio signals from a constellation of earthorbiting satellites, earth based receivers can computehighly accurate three dimensional geographiccoordinate positions.

If data on the satellite geometry, position, andmovement (called ephemeral data) are known, thedistance to an earth based receiver can be geometricallycalculated by measuring the time it takes for the radiosignals from four separate satellites to reach thereceiver. This type of positioning is only possiblebecause of the accuracy and speed of modern clocksand computers. Ephemeral data are constantlymonitored by a network of earth tracking stations andrelayed back to the satellite where they are included inthe transmitting signal and tracked by the GPS receiver.The GPS system consists of 28 satellites in 12-h polarorbits at 12,000 miles above the Earth's surface (EPA,1999b). This is su�cient to allow at least four satellitesto be available in any location at any time. The satellitestransmit a sequence of pseudo-random binary values(zeros and ones) that repeat over a speci®c time interval.The receiver determines the o�set in time between thereceived codes and the expected codes over the sametime interval, and converts this to the distance(pseudorange) to the satellite. If this ranging processis repeated constantly from at least three satellites, andknown errors caused by clock timing and atmospherice�ects are modeled, a precise position can be calculatedand referenced to a known datum and coordinatesystem. Because the receivers (which can be small,inexpensive hand-held devices) do not have the sameextremely accurate time-keeping systems as the satel-lites, the fourth necessary element, time, can bedetermined by using a fourth satellite signal. Inaddition to the ranging codes, the satellites alsoregularly transmit corrections for their predictedpositions. These corrections are determined by theGPS ground stations around the world, which monitorany drift that may occur in the satellites' orbits.

An important limitation of the GPS system is that ituses very weak radio signals. This means GPS receiversrequire unobstructed lines-of-sight to the satellites, andthey will generally not work inside buildings, or evenunder trees or in ``urban canyons'' (city streetssurrounded by tall buildings). Using larger antennae,such as those on backpack mounted units, some forest-canopies or other low-impedance obstructions can betolerated.

How accurate is GPS?

Accuracy depends on several factors including thedesign of the receiver. There are two general classes ofGPS receivers: navigation and geodetic. Navigationgrade instruments use only the ranging-codes todetermine positions, and can routinely yield accuraciesin the 2±5 m range. The geodetic quality units cancompute coordinates with millimeter level accuracy, byusing not only the ranging codes, but by alsomeasuring the phase-o�set between the internallygenerated signal and the carrier wave of the satellitesignal. Geodetic GPS measurements require carefulacquisition of the GPS signals over a fairly long timeinterval (in the order of 15 min), making it unsuitablefor many survey applications.

In the recent past the GPS signals that are availableto general public (C/A-code) contained an arti®cialerror of up to 100 m that is added by the US Militaryfor security reasons. This is known as ``SelectiveAvailability (SA)''. A single GPS unit is thereforeonly accurate to about 100 m. Using two units, onestationary, over a known geodetic control point, andone mobile, the Selective Availability can be removedeither in real time, through direct communicationbetween the two units, or after the survey during post-processing of the data, this is known as di�erentialcorrection. However, as of 1 May 2000, under thedirection of President Clinton, the US military stoppedthe intentional degradation of the GPS signal. With SA``turned o�'' civilian users of GPS will be able topinpoint locations up to 10 times more accurately thanbefore (White House, 2000a). For standard GPS unitsnot using di�erential correction techniques, this meanspositional accuracies between 20 and 30 m will bepossible (White House, 2000b). Even with the turningo� of SA, positional accuracy will be superior usingdi�erentially corrected GPS data. With this postprocessing technique (or in realtime with DGPSUnits) positional accuracy between 1 and 5 m ispossible. Which type of data are best for a givenapplication depends on the spatial sensitivity of thedata. For example, the location of a water qualitysample point 10 miles o� shore may be reasonablylocated using a standard GPS unit with 20±30 maccuracy. If the sample point is located well within theboundaries of a homogeneous cover type or land formthen the 20±30-m accuracy may be su�cient. However,if the sample point needs to be spatially distinguishedfrom other close-by sample points, DGPS is required.

Applications

Apart from the traditional types of geocoding, survey-ing, and the collection of accurate latitude/longitude


coordinates, one of the main applications of thistechnology is in the area of GIS. Global PositioningSystem technology provides a means of evaluating andquantifying the spatial accuracy of digital map data aswell as creating digital cartographic data structures.Potential products and application areas include directdigital mapping and ®eld navigation.

In direct digital mapping portable GPSs can be handcarried or mounted on vehicles to create digital datastructures that can be used as direct input into GISsystems. The system is used to update existing mapdata, provide highly accurate subsections, or createentirely new map products.

In ®eld navigation, ®eld sampling teams can useGPS to easily and accurately record the location ofspeci®c sampling locations or to navigate back to aprevious sampling point even when surface markershave been disturbed or are no longer present.

One application integrating GPS data into GIS databases involves, once again, the investigation of Section404 of the CWA violations. Already mentioned in thispaper is the geo-referencing of sets of current andhistorical aerial photography covering and area underinvestigation. This process establishes coordinate valuesfor each pixel in each photograph. The GPS receiver canrecord coordinate values at sample points or alongboundaries of features of interest. Once thesecoordinate values are recorded they can be downloadedand automatically overlayed on the geo-referencedaerial photography. This allows the analyst to applythe attributes determined in the ®eld to the signaturesseen on the aerial photography ( for example, soilsmoisture conditions, vegetation community composi-tion, or the outlines of ®ll areas or structures). Inaddition, changes to the site or changes in the locationsof features relative to their historic conditions asdepicted on the aerial photography will be apparentusing this overlay technique.

Sample points can also be plotted on the aerialphotography to show the spatial arrangement over thesite and to determine if adequate spatial coverage wasobtained during a survey. With new GIS/GPS inter-faces this can be done in near realtime using a laptop inthe ®eld. Additional sample points can then be taken asnecessary. On one recent investigation it was deter-mined, after review of the GPS sample point locations,that additional sample points were required to givebetter spatial coverage and the ®eld work was adjustedaccordingly.

The GPS data, whether sample point locations or theboundaries of signi®cant environmental features or con-ditions, are stored in a GIS for later analysis and pre-sentation. Large format thematic maps or digital aerialphotos can be plotted along with the geo-referencedsample point locations and features of interest.

Quality control

A carefully planned GPS survey can provide ®rst ordercontrol locations which can then be utilized to assessthe spatial quality of other thematic overlays that havebeen developed for the database or to georeference rawdata layers, such as satellite or aerial images.

Network modeling

Kinematic (mobile) positioning techniques can be usedto create network structures with much greater accuracyand precision than is currently possible. Spatialvariations in movement and rate, and time seriesanalysis can be acquired at greater data resolutions.

Photogrammetry QA

Photogrammetry and cartography often remain themost cost e�ective methods of creating thematic maps.The ease of establishing a control con®guration forexisting aerial photographs with GPS technology asopposed to traditional surveying methods can result insigni®cant savings in cost, time, and manpower.

Future Directions in Handling SpatialInformation

Spatial information technology is still rapidly develop-ing. Current trends show a convergence of GIS andnavigation components into many aspects of businessand even everyday life. Geographic InformationSystem software is evolving from large, proprietarysystems to modular, component-based systems thatprovide speci®c functionality. Common business pro-ductivity software can now be enhanced with these GIScomponents, putting spatial analysis tools in the handsof any user. Common standards for the developmentand maintenance of GIS data are being developed andare increasingly supported by the major softwaredevelopers. GPS receivers have become more ubiqui-tous, and are being integrated into wireless telephones,automobiles, computers and other appliances. Finally,the accessibility of GIS data and functionality throughthe Internet will mean that information from almostany environmental project can be quickly integratedinto a GIS database and made available for use by allparticipants, wherever they may be.

Acknowledgements

We wish to acknowledge Donald Garofalo, U.S. EPA,and Ricardo Lopez, U.S. EPA, for their review andcomments.

References

Arono�, S. 1995. Geographic Information Systems: A ManagementPerspective. Ottawa, WDL Publications. pp. 294.

Brilis, G.M., Gerlach, C.L. and van Waasbergen, R.J. 2000. Remotesensing tools assist in environmental forensics. Part I: traditionalmethods. Environmental Forensics 1, 63±67, doi:10.1006/enfo.2000.0009.

USEPA (U.S. Environmental Protection Agency). 1992a. LocationalData Policy GuidanceÐGuide to the Policy (OIRM, EPA/220 B-92-008, March 1992).

USEPA (U.S. Environmental Protection Agency). 1992b. GISTechnical Memorandum 3: Global Positioning Systems Technol-ogy and Its Application in Environmental Programs (ORD, EPA/600-R-92-036, February 1992).


Geospatial Metadata. 1997. National Spatial Data Infrastructure,Federal Geographic Data Committee Fact Sheet. March1997, http://www.fgdc.gov/publications/documents/metadata/metafact.pdf.

Grip, W.M., Grip, R.W. and Morrison, R. 2000. Application ofaerial photography in environmental forensic investigations.Environmental Forensics 1, 121±129, doi:10.1006/enfo.2000.0014.

White House, O�ce of the Press Secretary. 2000a. Statement by thePresident of the United States' Decision to Stop Degrading GlobalPositioning System Accuracy, 1 May 2000.

White House. 2000b. Improving the Civilian Global PositioningSystem (GPS), 1 May 2000.

Notice

The U.S. Environmental Protection Agency (EPA),through its O�ce of Research and Development(ORD), partially funded, collaborated, and performedpart of the applications described here under contractnumber 68-C5-0091 to Lockheed Martin Corporation.This manuscript has been peer reviewed by EPA andapproved for publication. Mention of trade names orcommercial products does not constitute endorsementor recommendation by the EPA.

remote sensing tools assist in environmental forensics:part ii—digital tools

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