Precise Estimation of Snow Water Equivalent based on GPS and Galileo Measurements

A precise information on Snow Water Equivalent (SWE) and Liquid Water Content (LWC) is essential for various applications, e.g. for optimized operations of hydropower plants, for improved flood forecast, and for cryosphere research.
Global Navigation Satellite System (GNSS) receivers and antennas can be used to measure the snow water equivalent, snow height and liquid water content. The GNSS receivers are much more cost-effective and easy to install than other sensors such as snow scales and pillows. Our set-up consists of two GNSS receivers/ antennas, whereas one GNSS antenna is placed on the ground (i.e. below) the snow and serves as actual sensor.
The other GNSS antenna is placed on a pole above the snow and serves as reference antenna. We use the pseudorange, carrier phase and carrier to noise power ratio observables from both GPS and Galileo. The pseudorange and carrier phase measurements of both GNSS antennas are combined in double difference measurements to eliminate orbital errors, clock errors and atmospheric delays.
The snow has three effects on the GNSS signals: The first one is a time delay caused by the reduced speed of signal propagation in snow. The second effect is the refraction at the air-snow interface according to Snell's law. The third effect is the signal attenuation which is mainly driven by the LWC.
These three effects of the snow affect only the lower GNSS antenna, i.e. the double differencing does not eliminate the effects of the snow. It only eliminates the atmospheric delays being common to both GNSS antennas.
The presentation covers a precise modeling of GNSS carrier phase and pseudorange measurements, and a mathematical description of the SWE and LWC estimation from the GNSS carrier phase, pseudorange and carrier to noise power ratio measurements. We investigate different parameterizations and evaluate their impact on the SWE solution. We show the measurement results for a snow monitoring station of ANavS at an Alpine test-site for the complete previous winter period 2023/ 2024.