Theoretical Study for Bare Soil Freeze/Thaw Process Detection Using GNSS-R/MR

摘要

GNSS-R remote sensing has emerged as a new promising remote sensing technique in the past two decades. It has gained wide attention at home and abroad. In essential, GNSS-R is a bistatic radar, the signals got by the GNSS-R receiver is delay Doppler map. Different from the specially designed receivers, the geodetic quality GPS receiver can be used to remotely sense the near surface soil moisture, vegetation growth and snow depth, i.e. GNSS-Multipath reflectometry (GNSS-MR). Three metrics, i.e. effective reflector height, phase and amplitude, are employed for retrieval. As for the applications of space-borne/air-borne GNSS-R or ground based GNSS-IR techniques, they include soil moisture, vegetation growth and snow depth retrieval. This paper has extended the bare soil freeze/thaw process detection, the theoretical fundamentals is that when the soil frozen/thawn process occurs, there is a big difference for the soil permittivity, which will result in the difference of reflectivities. The dielectric mixing models are employed for the calculations of the frozen/thawn soil permittivities, which are the inputs for the reflectivity models, the coherent scattering model and the random surface scattering models are employed for the calculation of specular scattering reflectivities and the diffuse scattering reflectivities, respectively. When the soil freeze/thaw process has occurred, the corresponding GPS multipath changes and the variations of delay Doppler map are simulated. The theoretical simulations indicate that the big difference of permittivity will result in the apparent changes of GPS multipath observables and delay Doppler map. It has been demonstrated in theory that the bare soil freeze/thaw process can be detected by the GNSS-R or GNSS-MR techniques.