ACCURACY OF A GLOBAL POSITIONING SYSTEM (GPS) FOR WEED MAPPING

Experiments were conducted to test the accuracy of a global positionin g system (GPS) in measuring the area of simulated weed patches nf vary ing size and to determine the accuracy in navigating back to particula r points in a field. Circular areas of 5, 50, and 500 m(2) were establ ished and measured using point and polygon features of a GPS. The GPS estimations of the area of those patches had errors ranging from 7 to 45%, 6 to 15%, and 3 to 6%, respectively, when compared to actual meas urements. As patch size increased, errors decreased. A curve describin g the relationship between GPS error and patch size had an excellent f it (r(2) = 0.92). The error remained the same in all measurements acro ss all patch sizes, but composed a smaller percentage of large patches . The GPS had submeter accuracy in navigation to the correct quadrat 7 3% of the time, located the correct quadrat 27% of the time, and invar iably navigated to within 1.58 m of the correct quadrat. The relations hip between patch size and measurement error was applied to natural in festations of hemp dogbane.