Soil Moisture Estimation from GNSS Multipath at the Field Research Station Marquardt, Germany

Ajeet Kunwar (Sucessful finalization January 2017)

Soil moisture is a key parameter in hydrological cycle. It is also an important component from a socio-economical perspective. Knowledge about soil moisture is beneficial for many applications such as agricultural, health, and water management programs as well as water related disasters management. Several techniques are in use, including in-situ and remote sensing to measure this parameter, soil moisture. However, the desiredaccuracy in the appropriate spatial and temporal resolutions remains a major challenge.

In this research, the capabilities of multipath signals from Global Navigation Satellite Systems (GNSS) have been evaluated by using a commercial geodetic quality receiver (JAVAD-TR-G3T: 15657) and antenna (Antcom: S67-1575-86) for estimating soil moisture. Early research has already demonstrated the capability of this method to evaluate the characteristics of land or ocean surfaces, such as height, roughness, or dielectric properties of reflecting surfaces. From there, various methods were applied to estimate geophysical parameters such as ocean topography, ocean surface, wind, vegetation, soil moisture and snow height.

The results obtained in this thesis using a commercial geodetic quality GNSS receiver and antenna system show promising potential for the measurement of soil moisture. This technique is very sensitive and provides a good response following the dynamics of the ground and precipitation events. This technique is capable of detecting changes or distortions of land surface properties, even in the excessive rainfall events and freezing ground temperatures. Absolute values of soil moisture measured from this technique depends on surface roughness and always show higher results than TDR. This difference is because TDR measurement is a point measurement and GNSS is an area measurement, and geometric dependent. The analysis shows that there is high correlation (more than 0.79) between TDR (at different depth: 1,3,5,9 and 11 cm) and GNSS multipath estimated soil moisture. This technique could provide an excellent supplementary data for many earth-orbiting missions such as SMOS, SMAP, and other Earth Explorer Mission in the future.