Applications of Ground-Based Multipath Reflectometry Based on Combinations of Pseudorange and Carrier Phase Observations of Multi-GNSS Dual-Frequency Signals

Measurements from a geodetic global navigation satellite system (GNSS) setup can be deployed to retrieve geophysics parameters, because coherent reflections from the surrounding environment enter the antenna along with direct signals. Previous GNSS multipath studies of snow depth and sea level were mainly based on signals-to-noise ratio (SNR) measurements. In this article, two new methods based on combinations of pseudorange and carrier phase observations from multi-GNSS dual-frequency signals are proposed, which can be used as substitutes for the SNR method when there are no SNR observations. The first method is based on the combination of dual-frequency pseudorange, which is geometry-free, and avoids any consideration of the influence of ambiguity and cycle slip of carrier phase observations. The second method is based on the combination of dual-frequency pseudorange and carrier phase. This, too, is geometry-free, and is not affected by ionospheric delays. To test these two methods, parameter retrievals using multi-GNSS observations reflected from different surface materials were applied. The derived snow depth series over a 256-day period from SG27 station showed an optimal RMSE of 8 cm with respect to
in situ
data for both methods by using the combination of observations from GPS L2 and L5 frequency bands. In addition, in a separate 365-day experiment at AT01 station, sea levels were estimated using the proposed methods with optimal RMSE of 21 cm when compared with tide gauge measurements. All these results indicate that the two proposed methods can be seen as supplements to the applications of ground-based multipath reflectometry.