Abstract
Five GPS receivers with point, differential and carrier phase positioning systems were tested. The test was done at four under canopy sites in flat forests without terrain effect and one extra-forest site. The point positioningreceiver was stable even inside forests and its mean horizontal positional accuracy of 5 min was 15.448.6 m. The differential GPS receivers successfully received real time DGPS correction broadcast from marine radio beacons and their accuracy were 1.17.3 m. The carrier phase receivers could not get fixed solutions and were not stable inside forests, but their accuracy of float solutions were 0.15.1 m, better than those of the differential receivers. The accuracy of both differential and carrier phase receivers decreased with increasing basal area. It was found that the accuracy of datum conversion, which the GIS software had, was not precise enough and it was necessary to use other conversion software to evaluate approximately 1 m accuracy. Selective usage of point positioning and differential GPS receivers is suggested for forest management.
