GPS has been used for a wide variety of environmental applications, both stand-alone and differential GPS receivers have been used, depending on the accuracy requirements. For general environmental surveys, a standard civil GPS receiver (non-DGPS) can be used if the application can tolerate the +/-100 m accuracy. Most environmental applications require some form of DGPS with its +/- 10 m accuracy. DGPS data is suitable for most mapping and geographic information system (GIS) applications. Several typical environmental applications are described below. Lake Water Quality Study Bechtel Environmental, Inc. of Oak Ridge, Tennessee performed an early GPS assisted water quality study in 1991 (5). Both stand-alone and differential GPS receivers were used to map sampling positions for PCB contamination on Hartwell Lake, located on the Georgia - South Carolina border. At that time, 1991, the GPS constellation of 24 NAVSTAR satellites was not fully in place, so a limited number of hours were available each day for GPS operations. During part of the study, Selective Availability was turned off by the DoD due to the Gulf War. Later in the study differential GPS, with a portable reference station was used (the U.S. Coast Guard DGPS system was not yet operational).

Oil Spill Tracking The National Oceanic and Atmospheric Administration (NOAA) developed a GPS based oil spill tracking system (6). An airborne tracking system consisting of a stand-alone GPS receiver and a custom datalogger was used to track oil slicks from the air. The datalogger was configured with custom keys to annotate the data record with flags on slick quality, appearance, and other characteristics. The system was first deployed on the Exxon Valdez oil spill. Data was post-processed and used to validate NOAA oil slick models. A GPS equipped drifter buoy was also developed by NOAA and the U.S. Minerals Management Service (MMS). Dropped into an oil slick by helicopter, the buoys drift along with the slick, and telemeter GPS coordinates via the TIROS satellite system. Radioactive Waste Contamination Survey

The Hanford Site in Washington State, was until the mid-eighties, the primary source of plutonium for the U.S. nuclear arsenal. After plutonium production at the site was stopped in 1989, a radiological survey of hundreds of square miles of potentially contaminated land was required. Westinghouse Hanford Company developed a unique monitoring vehicle called the Mobile Surface Contamination Monitor (MSCM – II). Based on a heavy duty four wheel drive farm tractor, the MSCM – II has sensitive scintillation counters mounted on a front-end loader arm. Data from the counters is processed by an on-board computer system and combined with latitude and longitude coordinates from and integrated with Geographic Information System applications.