Using Global Positioning Systems To Increase Accuracy in Soil Survey Field Mapping

By Jim Turenne (This article was written and posted in 1996 some information may be outdated).

Using GPS, GPR, and GIS to inventory peat deposits
Instructions on how to download GPS data and create contour maps


A soil survey update is underway in Plymouth County Massachusetts. The updated soil survey report is employing state of the art technology such as ground penetrating radar, high resolution CIR photography, and global positioning systems (GPS) to produce highly detailed and accurate soil maps. The updated soil mapping is at a scale of 1:12,000, which allow minimum delineations down to 1 - 2, acres.

Rockwell PLGR GPR

The Global Positioning System used by the Plymouth County Soil Survey is the Rockwell International Precision Lightweight GPS Receiver (PLGR). The PLGR unit measures approximately 10x4x2 inches and weighs 3 pounds with batteries. The small size and lightweight make the unit easy to carry and use. The durable plastic case is sealed for all-weather use. The unit has a built in antenna and has external connectors for power, antennas, and other accessories. The PLGR unit provides accuracy to within 4 meters. The PLGR unit has special encryption codes, which allows for increased accuracy with out the need for post-processing.

Using GPS for Field Soil Mapping

The GPS unit was field tested by the Plymouth County Soil Survey in 1994 to determine the potential use of the PLGR's for the Survey. Initial field tests involved determining the accuracy of the unit by locating known areas and comparing the coordinates to determine the accuracy. Coordinates from the PLGR were downloaded onto a PC and Digital Ortho-photography was overlain to see if the PLGR's location matched the known location of the imagery. The GPS unit accurately plotted the correct location for the scale of the field mapping. The next step was to determine its uses for field mapping.

The GPS unit is carried in a fanny pack along with other equipment used by soil scientists. When a location is required the GPS unit displays the coordinate and stores the location for geo-referencing. The easiest coordinate system to use in the field is the UTM coordinate system. This system is based on a 1,000-meter grid, which is shown on most USGS topographic maps. A Mylar overlay of the topographic map is enlarged to match the scale of the aerial photo so the location of site can be pinpointed by the mapper. Results of the field-testing showed that the GPS provides a wide array of uses for soil survey. The following is a brief list of some uses for the GPS for soil survey operations:

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