Abstract
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.
Highlights
T HE SIGNALS from global navigation satellite system (GNSS) were originally used for positioning, navigation and timing
At AT01, in order to filter out the reflected signals from surrounding obstacles and isolate the reflected signals from the sea surface, the elevation and azimuth ranges are set as 5°–15° and 40°–220°, respectively
Different combinations of dual-frequency pseudorange and carrier phase are formed in accordance with the GNSS observation data using (6) and (10)
Summary
T HE SIGNALS from global navigation satellite system (GNSS) were originally used for positioning, navigation and timing. GNSS multipath reflectometry (GNSS-MR) [1] is one of these that relies on the reflected signals which were received simultaneously and coherently with direct satellite signal by geodetic receivers. In contrast to other kind of GNSS-R that use specially designed instruments to, respectively, receive the direct and reflected signals, geodetic receivers only measure the interference of the direct and reflected signals [2]. Rodriguez-Alvarez et al [4] extends this kind of GNSS-R which based on the measurement of the interference pattern of the GPS direct and reflected signals to a snow covered soils studies. Signal-to-noise ratio (SNR), observable in GNSS receiver independent exchange format (RINEX) files, is the conventional measurement in GNSS-MR for retrievals of environmental parameters such as the sea level [5,6,7,8,9,10,11,12,13,14,15,16,17]; snow depth [18]–[28]; soil moisture [29]–[35]; vegetation growth [36]–[40]; etc
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