Global Positioning Systems (Gps)

Article excerpt

Accurate pacing, compasses, and night-sky navigation now share the outdoors with GPS systems and laser range finders. Field collection will never be the same.

GPS allows field researchers to pinpoint the location of observations (reportedly to within an inch or less with the most sophisticated systems). The US Department of Defense (DOD) manages a constellation of twenty-four satellites in high-altitude orbits, which continuously broadcast precise time and position data. By measuring the interval between transmission and reception of satellite signals, and triangulating data received from at least three satellites, a GPS receiver calculates a position fix, and displays it as longitude/latitude, map grid, or military grid coordinates. For species inventories, it makes for much more useful reporting than old systems that referenced names of towns, political boundaries, physical features, or other changeable markers.

In May, GPS became faster, more accurate, and less costly when President Clinton turned off the DOD's selective availability (SA) system. Using SA, the Defense Department had intentionally corrupted satellites' timing signals, in order to make readings less accurate to potential hostile users.

The basic item in a GPS "toolkit" is a GPS receiver. Most are manufactured by Garmin, Magellan, or Trimble (see their Web sites or a mail-order catalog such as Ben Meadows Company, 800/241-2068, www.benmeadows. …