Abstract
Accuracy of positioning with DGPS (Differential GPS) was studied in various forests. Almost all positions of measurements by DGPS affected by SA (Selective Availability) located within a 1m circle. The more DGPS located near the tree stem, the more positioning errors became large. Significant differences were observed in the positioning errors between outside and inside of the evergreen broad-leaved and the evergreen coniferous forests, but not the deciduous forest. These results suggested that it was necessary to use DGPS at a point that was far away from the tree stem and with an open upside canopy, and to use DGPS in winter inside the deciduous forest. In addition, when we use DGPS inside the forest, for example for measuring every tree, we can enhance the accuracy of positioning by offset positioning using a laser range finder from the position that is far away from the tree stem and with an open upside canopy.
