A first attempt to retrieve dry snow density and snow water equivalent using signal-to-noise ratio observations from geodetic GNSS receivers

Snow density (SDE) and snow water equivalent (SWE) are critical snow variables. The geodetic Global Navigation Satellite System (GNSS) receiver has been proven to estimate snow depth using the phase change rate of the signal-to-noise ratio (SNR) observations. However, it is challenging to retrieve SDE and SWE due to the difficulty in extracting the reflected amplitude since it hides in the SNR interference waveform and changes with the satellite elevation angle. This study first explores the feasibility of simultaneously retrieving SDE and SWE using GNSS SNR observations. A novel GSARM model was proposed that relates the corrected instantaneous amplitude ratio (<i>α</i>) to the snow permittivity and the resulting SDE and SWE. The GSARM results are compared with three other data sources, i.e., the PBO-H₂O, the ERA5-Land, and the in-situ measurements over three GNSS sites. The overall Root Mean Square Deviation (RMSD) values of SDE for GSARM versus PBO-H₂O, ERA5-Land, and in-situ measurements are 0.04 g/cm³, 0.04 g/cm³, and 0.04 g/cm³, respectively. The overall mean (R², RMSD, and MAE) of SWE for GSARM versus PBO-H₂O, ERA5-Land, and in-situ measurements are (0.91, 18.07 mm, and 14.83 mm), (0.78, 20.44 mm, and 18.54 mm), and (0.90, 17.09 mm, and 14.81 mm), respectively. The findings of this study prove the feasibility of using geodetic GNSS receivers for SDE and SWE retrieval and achieving similar accuracy to traditional radiometers. It also has great potential to develop low-cost instruments for snow monitoring based on principles investigated in this study.