Forest canopy influence on the precision of location with GPS receivers

Abstract

This article presents the results of a test of three GPS receivers of GIS category (Topcon Turbo G1, Topcon, Magellan ProMark X-CM, Magellan, March II-E, Corvalis Microtechnology) in location under the entire cover of forest canopy. A network of 111 experimental points was established in the territory of Training Forest Enterprise (TFE) of the Technical University Zvolen, Forest District Kováčová, in variable forest and terrain conditions. Location of the points was measured by an exact terrestrial geodetic method and consequently by all receivers. To evaluate the location precision of each receiver we used the method of calculation of individual differences in co-ordinate values for each measurement, and calculation of average differences and their standard deviations for groups of measurements. The values of average co-ordinate errors and testing of the presence of systematic error were also calculated. To evaluate the influence of receiver type, stand age, tree species composition and terrain configuration multi-factor analysis of variance was used. General location error was 7.16 m for Topcon, 5.89 m for Magellan and 5.60 m for March. Difference between Topcon and the other two receivers is statistically significant. The influence of forest stand age is also statistically significant. The results of the test of tree species composition and terrain configuration influence are not unambiguous.