Preliminary Evaluation of Baseline Relative Accuracies Using L1 Frequency Observations of Navigation-Grade GARMIN Receivers

Abstract

Handheld navigation global positioning system (GPS) receivers are significantly cheaper and their position determination accuracy is less than their geodetic-grade counterparts. Although the main observable in most low-cost handheld GPS receivers is the coarse acquisition (C/A) code, some receive L1 frequency observations and utilize them to smooth the code measurements. In this technical paper, we examined the use of the C/A code and L1 phase observations captured by two GARMIN eTrex receivers in a postprocessing mode. We used software applications that send low level commands to download and save the receiver data stream and convert the observations into standard RINEX file format. Nineteen baselines with different lengths were observed using the eTrex receivers and dual frequency geodetic-grade receivers. The baseline lengths were derived from the eTrex observations and compared to corresponding ones derived from the higher accuracy geodetic-grade receiver observations. Several tests were conducted to analyze the effect of potential error sources on the achieved accuracy. The results showed that low satellite angles and existing cycle slips contributed to the errors in the processed eTrex data. The implementation of a cycle slip detection algorithm and their subsequent deletion significantly enhanced the obtained baseline relative accuracy to a finally limited range of 1.8–13.4 cm/km.