INITIAL RESULTS FOR NEAR SURFACE SOIL FREEZE-THAW PROCESS DETECTION USING GPS-INTERFEROMETRIC REFLECTOMETRY

The geodetic-quality GPS receivers can be used for geophysical parameters retrieval, i.e. soil moisture, vegetation growth and snow depth, and it is called GPS-Interferometric Reflectometry (GPS-IR) remote sensing. In this paper, to detect the near surface soil freeze-thaw process using GPS-IR is evaluated for the first time. When the soil changes from frozen state to thawn state, the corresponding permittivities and reflectivities at RR, LR, VR and HR pol are changed. Triple-frequency effects are evaluated, for different frequencies, the modulations for SNR data are not the same, but within L-band, the observed surface has almost the same reflected properties (e. g. GPS L1 band, L2band and L5band). A GPS site in the EarthScope Plate Boundary Observatory (PBO) and a corresponding soil climate site in SCAN (Soil Climate Analysis Network) is used to examine the potential for near surface soil freeze-thaw process detection. Two representative days and a time series of SNR data show strong correlation with near surface soil temperature. Our initial results demonstrate that GPS-IR has the potential for bare soil freeze-thaw detection. Therefore, the new low-cost bare soil freeze-thaw monitoring networks are expected from geodetic GNSS network.