An Improved Change Detection Method for Soil Moisture Retrieval using Sentinel-1 and Smap Data

In this paper, an improved change detection method (ICDM) is proposed to obtain the soil surface moisture (SSM) with a resolution of 20 meters, which greatly improves the resolution of SMAP soil moisture products. First, NDWI was calculated using a time series data of Sentinel-2 and then converted to vegetation water content (mveg). With the help of the water cloud model, the influence of vegetation on the backscattering coefficient is eliminated. Then, in order to make the change detection method (CDM) more reasonable, a method for removing influence of roughness change on backscattering coefficient is proposed. It uses the difference between co-polarization and cross-polarization ( σ0
^vv
- σ0
^vh
) for roughness normalization. SSM was obtained by combining the soil relative moisture retrieved from the time series data of Sentinel-1 with the maximum and minimum water content of the study area within one year obtained from the SMAP data. The results showed that the MRE of SSM extracted by ICDM was 8.34%, which was less than 17.49% of CDM.