Dynamic accuracy of recreation-grade GPS receivers in oak-hickory forests

The study, using 20 individual instruments of one model of recreational-grade Global Positioning Systems (GPS) receiver, was conducted in a mature predominantly deciduous forest in the southern United States. The true area was delineated from the eight test points that were very accurately located from monuments using survey-grade instrument and protocols, within the Whitehall Forest GPS Test Site in northeast Georgia. These sameeighttestpointswereusedascontrolsduringthedynamichorizontalaccuracyassessmentsofGPStechnology conducted within the forest. The test points are very precise compared with recent published literature. Our hypotheses were that the areas determined with the 20 receivers were not significantly different from the true areas, and the percentage of the area of agreement and the variation of the vertices around the true boundary were not different in winter and summer seasons. Also, based on the distribution of the vertices around the true boundary, we conducted simulations for larger areas. The average area of agreement was 93 per cent during the winter season, and 84 per cent during the summer season. The variation in sample areas was also greater for data collected during the summer, and data from the winter had higher association as measured by area of agreement with the true study area than data from the summer. A ranking of receivers by average area during each season did not reveal significant problems within the set of receivers tested. In conclusion, data collected during each season were not significantly different. Given the distribution of vertices around the true boundary of the study area, simulations of larger land areas revealed that there would be a 2 per cent or less error for mature, deciduous forests of greater than 25 ha in size in both winter and summer seasons.