Carrier phase multipath corrections based on GNSS signal quality measurements to improve CORS observations

Abstract

Carrier phase multipath caused by reflections in the vicinity of GNSS stations is a major error source of precise differential positioning. Detection and mitigation of carrier phase multipath errors can be based on signal quality measurements, i.e. signal-to-noise ratio (S/N) or carrier-to-noise ratio (C/N), as provided by GNSS receivers. Variations of the signal quality oscillation frequency are caused by changes of the reflected signal's additional path length. Calculating carrier phase multipath corrections from signal quality time series is not simple. Most published algorithms need various interim results, e.g. phase shift or attenuation factors, to calculate the final correction value. Our algorithm, however, directly estimates carrier phase multipath corrections from signal quality measurements. In order to validate the potential of this multipath mitigation method in practice, GPS/GLONASS observation data sets of six continuously operating reference stations (CORS) of the German SAPOS network were corrected. All these stations are equipped with receivers for which the signal quality based multipath mitigation performs similarly well for both frequencies. Thus multipath mitigation may even improve coordinate results based on the ionosphere-free linear combination. We present a detailed analysis of the effects of carrier phase multipath corrections on positioning results in this CORS subnetwork.