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Library Card

Karsky, Dick ; Chamberlain, Ken ; Mancebo, Santiago ; Patterson, Don ; Jasumback, Anthony E.. 2001. Comparison of GPS Receivers Under a Forest Canopy After Selective Availability Has Been Turned Off. 0171 2809. Missoula, MT: U.S. Department of Agriculture, Forest Service, Missoula Technology and Development Center. 18 p.

Describes tests of various GPS receivers (Rockwell PLGR +96, Garmin GPS III+, Trimble Pro XR, Trimble GeoExplorer 3, Magellan Map 410) at several locations (Powell, ID, Lubrecht, MT, Clackamas, OR). A good satellite constellation (satellites with strong signals within the GPS receiver's view) is needed to get good data. When the satellite constellation is good, the inexpensive handheld receivers will provide accurate positions in the open or under a medium canopy. The handheld receivers are not as accurate under a heavy canopy, especially when the satellite constellation is poor. Postprocessing data increases position accuracy, typically by 2 to 4 meters. If data are not needed immediately, it is more efficient to collect uncorrected data and postprocess the information rather than to collect real-time or DGPS positions. This may change in the future when more DGPS stations come online and all areas can receive a DGPS signal from two beacon stations.

Keywords: accuracy, antennas, real-time, satelites, surveys

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