利用 GNSS 信号地表穿透特性反演土壤湿度的思考

It has been widely concerned by domestic and foreign research institutions that make the Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) used in soil surface moisture inversion because of its excellent characteristics, needing not for signal sources, suiting wide detection area, etc. In order to solve the complex problem of tradition GNSS penetration model, a method was proposed to calculate the vertical distance between the antenna phase center and the actual surface reflector by GNSS-IR according to the geometric configuration. Firstly, the height measurement deviations under different soil moisture were calculated by simulation, establishing the linear relationship of the GNSS signal with the theoretical penetration depth and the inverse proportion relationship with soil moisture. Considering the influence of the change of the satellite altitude angle on the altitude retrieval, a modified altimetry model was adopted, and the Lomb-Scargle spectral analysis method was used to calculate the altitude measurement deviation. Then, in order to reduce the influence of surface vegetation on the vertical distance between the inversion antenna phase center and the actual surface reflector, a normalized vegetation index was used to correct the height measurement deviation. And, a first-order inverse proportional model of GNSS signal height measurement deviation and soil moisture was established. Finally, verification experiments were carried out for the proposed models. The results show a better effect of the application of the GNSS signal surface penetration characteristics in the soil moisture inversion for the scene of long-term large-scale changes in soil moisture.