Research On GNSS-IR Algorithm For Retrieving Soil Moisture Parameters

Soil moisture is Soil moisture is the water stored in the upper soil.It is a key variable in various processes and applications,such as numerical weather forecast,flood forecast,agricultural drought assessment,water resource management,greenhouse gas accounting,etc.Existing soil moisture monitoring methods(such as drying and weighing,remote sensing observation,hygrometer measurement,etc.)have the disadvantages of high cost,low spatial and temporal resolution,destruction of observation objects,time and effort,and long repeated observation period.The environment around the GNSS station will have a multi-path effect on its observations.How to use the multi-path effect has attracted the attention of scholars at home and abroad.With the continuous deepening of the research and application of global satellite navigation systems,the topic of inversion of the environmental parameters around the station based on the signal-to-noise ratio information represented by the GNSS-IR technology has become a new research hotspot,which makes The field of surface remote sensing is emerging.The use of GPS signals based on microwave L-band for soil moisture monitoring has the advantages of low cost,high time resolution,strong real-time performance,and high automation,which has attracted the attention of many scholars.The main research contents and results of this article are as follows:1.Briefly describe GNSS signal propagation theory.The coverage area and physical characteristics of the reflected signal are discussed.The basic principles and basic processes of soil moisture inversion using GNSS-IR technology are described.And use the measured data to verify.The correlation coefficient between single star phase and soil moisture is basically above 0.8.2.In the process of inverting soil moisture using GNSS-IR technology,the single-star results are unstable and the reliability is not high.A weighted fusion method is proposed to obtain multi-star soil moisture inversion results.Experiments show that weighted fusion can effectively improve the accuracy and stability of inversion results.The linear correlation between forecast and actual data reaches 0.96.3.Using experimental data,it is proved that the frequency of the signal-to-noise ratio residual sequence can theoretically be used to invert soil moisture.In view of the problem of excessive signal noise in the actual environment,which makes it difficult to use the frequency of the reflected signal,a method of side observation is proposed,which effectively reflects the changing trend of soil moisture.The correlation coefficients of the results of the side observation method at the two stations are 0.68 and 0.73.4.Summarized the technical advantages and characteristics of soil moisture inversion using GNSS-IR technology.And look forward to the problems encountered in the development of this technology and the direction of further development.With the gradual improvement of CORS networks in domestic cities,it is particularly important to use GNSS-IR technology to expand the application of ground reference stations.