Study On Remote Sensing Of Soil Moisture With Satellite Signal-to-noise Ratio Based On GNSS-R

Soil moisture(soil water content),plays an important role in the whole climate and ecological environment.It is an indispensable component of the water cycle and one of the important factors affecting crop yields and the desertification ecological environment.Therefore,the accurate measurement and prediction of soil moisture provide important data sources for ecology,agriculture,climate,disaster prevention and control.In recent years,GNSS-R remote sensing technology based on multi-path effects has provided a new and efficient monitoring method for soil moisture.How to use GNSS-R technology for soil moisture remote sensing has become a hot research topic.On the basis of reviewing the research status of GNSS-R technology at home and abroad,this paper has carried out systematic and in-depth research on the remote sensing of soil moisture based on GNSS-R technology principle and reflected signal characteristics.Around this system,we carried out the following studies:(1)This paper studies the expression of soil moisture and traditional measurement methods,and summaries the two techniques based on GNSS-R technology for soil moisture measurement: dual-antenna model based on reflected signal power and singleantenna based on multi-path component of signal-to-noise ratio.The relationship between multipath effect and SNR is discussed in detail,and the reason why the signalto-noise ratio oscillates at low elevation angles is pointed out.(2)This paper studies and explores the detection range of remote sensing of soil moisture based on GNSS-R technology.From the perspective of detection depth and detection area,the Lomb Scargle algorithm and Fresnel reflection zone is introduced to reasonably determine the soil moisture detection area.(3)This paper studies the method of extracting multi-path component characteristic parameters from SNR for single antenna mode.On this basis,the soil moisture inversion package SNR_SM based on Matlab platform is designed and developed.(4)This paper studies the experimental data of a rainfall event and analyzes the variation of the signal-to-noise ratio multi-path characteristic parameters of four satellites.The experimental results show that the variation regularity of multi-path characteristic parameters of four satellites is consistent.With the increase of soil moisture,the delay phase increases,the frequency and depth of detection decreases,the amplitude increases,which verified the feasibility of inversion of soil moisture through characteristic parameters.(5)Based on the measured data of 31 days of the 17 th satellite,the soil moisture inversion model is established from delay phase,depth of detection,and amplitude of the SNR multi-path component.By comparing with the measured soil moisture data,it is found that there is a good linear relationship between the delay phase and the soil moisture,and the exponential model fitting of the detection depth and amplitude is slightly better than the linear fitting effect.(6)Based on the data of before and after snow,summer and winter,the center of playground and around playground,this paper analyzes the effect of snow thickness,seasonal variation,and soil medium on the SNR data.