Application of dual-frequency GPS receivers for static surveying under tree canopies

Abstract

 The objectives of this study are to evaluate the accuracy of dual-frequency GPS receivers in static surveying in forests and to develop a model to estimate the probability of resolving ambiguity by logistic regressions, with independent variables being the observation period length and an index of canopy opening. In this study, a rover receiver was set up at four points in the forest (at a treeless point, under a large canopy gap, under a small canopy gap, and under closed canopies), and static surveys were conducted for 4 h at each point. The observed data were post-processed with the data from the base station, and the baseline data were repeatedly post-processed while changing the length of the observation periods. As a result, positional accuracies were decreased more under tree canopies than at the treeless point, but under tree canopies several integer ambiguities were resolved within 15 min by using a dual-frequency GPS receiver. The result also showed that ambiguity-fixed solutions using a dual-frequency GPS receiver produced the most accurate positional data under tree canopies. Moreover, the probability of resolving ambiguity was estimated by logistic regression with the independent variables being the index of canopy opening and observation period lengths.