A ground-based GNSS-R station for soil moisture monitoring

GNSS-R is an emerging technology for remote sensing of soil moisture with the advantages of high tempo spatial resolutions at low cost. Most of the current research has been carried out on the basis of space borne observations, and a large number of results have been obtained. Due to the high altitude of satellites, the Fresnel reflection zone is usually a few kilometers in diameter, which does not meet the requirements of fine agriculture. Ground-based and UAV-borne GNSS-R, due to their low altitude, can provide effective observations to address above problem. We have built a ground-based GNSS-R observatory at the Experimental Farm of Weihai Academy of Agricultural Sciences, Shandong Province China. The site is equipped with mainly high gain a downward facing left-handed circularly polarized antenna, an upward facing right-handed circularly polarized antenna, an IF signal collector and a computer platform for running the SDR. Currently the main observables that can be output include: SNR, Power Ratio, DDM, etc. The retrievals were evaluated by the in-suit measurements from TDR and the results show that the accuracy of the solutions can reach 3%. In addition, a UAV-based GNSS-R setups are also built and effective measurements were obtained.