Conference Agenda

In this paper, snow depth is derived using GPS Interferometric Reflectometry (GNSS-IR) and a method is presented to derive snow water equivalent (SWE) by using refracted GPS signals (GPS refractometry) from an antenna buried underneath the snow pack. The GPS monitoring system is installed at the narrow Grimsel mountain pass located in the Swiss Alps and is surrounded by high mountains. The GNSS-IR retrieved snow depth shows a certain correlation to the reference snow depth. The terrain influences thereby the precision of the retrieved snow depth seriously. GPS refractometry is able to correct the influence of the snow pack above the buried antenna. The systematic and stochastic snow induced effects in the GPS residuals are significantly reduced by estimating the SWE above the antenna. The method is thus able to estimate the SWE. Results of refractometric determination of the SWE show a very high correspondence within less than 5% with the results of conventional SWE determinations. This has be shown over three consecutive winter seasons.

Soil moisture plays an important role in water cycle study. Modern remote sensing technique has demonstrated that L-band is very sensitive to soil moisture variation. With the design and implementation of the Global Navigation Satellite System (GNSS) which working on L-band as well, remote sensing using navigation signal of opportunity gained wide interests. With two decades’ development, two technique based on signal reflection have been proposed including GNSS-R (GNSS-Reflectometry) and GNSS-IR (GNSS-Interferometric Reflectometry). More recently, some researchers tried to utilize the penetrating signal to measure soil moisture (Franziska Koch et al., 2016) and snow water equivalent (Franziska Koch et al., 2014 and Ladina Steiner et al,. 2018). For the soil moisture measurement, the investigation of the penetrating signal leads to better understanding of the sensing depth of the reflected signal, which is related to estimating the Root-Zone soil moisture and Field Capability.

We are going to study how different soil moisture affect the signal attenuation in the soil and the penetration depth of the signal under different soil moisture condition. We hope to predict the reflection caused by the soil based on the above analysis. Finally, we want to analyze the sensing depth of the GNSS signal which is defined as the maximum depth from where the signal reflected off can be received under certain receiving sensitivity. A long term experiment is carried out along with this study. Two identical antennas are used with one placed in the air and the other is placed at the bottom of a big plastic bag filled with soil of different thickness. At the same time, three FDR soil moisture probes are evenly buried at vertical direction with one probe always stay at the bottom of the bag. The increment of soil thickness is about 2 cm with its initial depth being 2 cm. Different navigation system will be investigated such as GALILEO and BEIDOU. Particularly, the BEIDOU System contains different kinds of satellite orbits including GEO, IGSO, and MEO. The GEO satellite can give quasi-static measurements, while the IGSO and MEO can give dynamic measurements.