DEVELOPING TOPOGRAPHIC MAPS USING A SUBâMETER ACCURACY GLOBAL POSITIONING RECEIVER

Abstract

Because spatial yield variability is usually related to topographic features, the availability of an accuratetopographic map should provide an opportunity to improve management of agricultural inputs. The objective of this studywas to develop a topographic map using a submeter accuracy differentialcorrected global positioning system (DGPS) andelevation data collected during routine crop management passes throughout multiple years. Two fields (24 and 31 ha) witha relief of 19 to 23 m were selected for this study. Elevation was obtained on 1s intervals using a RealTimeKinematic (RTK)GPS mounted on a pickup truck and driving passes on 3 to 50m intervals (greater distances for relatively uniform areas).Elevation was also obtained from multiple (six to seven) passes (4 to 14m intervals) with a DGPS mounted on a tractor,sprayer, or combine (1 or 2s intervals). Elevation data were interpolated to a 5m grid. Mean elevation from everycombination of passes with the DGPS was compared to elevation from the RTK GPS using the root mean square error (RMSE).A simple linear regression was used to compare the average elevation from the DGPS (based on all passes) to the RTK map.Threedimensional wireframe surfaces developed from the RTK GPS and DGPS data and several transects across thesesurfaces were used to evaluate the success of using the DGPS data. The RMSE decreased from 0.63 and 0.75 with one pass,for Fields One and Two, respectively, to 0.39 with six and seven passes, respectively. Average elevation, as determined fromsix or seven passes with the DGPS, was linearly related to elevation from the RTK GPS (r2 > 0.99). Although absoluteelevation differences were sometimes > 1 m, the DGPS maps were effective in characterizing the dominant topographicfeatures of both fields. Features as small as terraces, which are probably smaller than a typical manageable unit, were evidentin the DGPS topographic map. Agronomically important topographic features were identifiable with a DGPS.