Carrier Phase Multipath Calibration of GPS Reference Stations

Based on available GPS reference network observations we developed, implemented and tested a procedure to estimate carrier phase multipath corrections. This procedure consists of three steps: detection and localization of multipath affected satellite signals, daily estimations of multipath errors, and combination of these daily estimates to corrections for undifferenced L1 and L2 phase measurements. We examined the variability of carrier phase multipath effects over one year in order to estimate the influence wetness and snow have on the reflectors. Whereas on days with continuous rainfall our multipath corrections worked as well as usually, on some days with snow cover multipath errors were altered. In order to prove the successful calibration and correction of carrier phase multipath errors, we compared the double-differenced residuals of short and of long baselines for both uncorrected and corrected observations. Multipath errors could be significantly reduced for often used linear combinations of the dual-frequency observations, but not for the original L1 and L2 observations themselves. The reason can be found in the small multipath effects compared to a larger influence of remaining ionospheric errors in the multipath corrections.