Inversion of soil roughness for estimating soil moisture from time-series Sentinel-1 backscatter observations over Yanco sites

Sentinel-1 provides improved temporal and spatial resolutions in comparison with previous satellite missions. Unlike the change detection method that assumes the time-invariance of surface roughness at a coarse resolution, this study spatially inverted roughness and soil moisture from Sentinel-1 backscatter. Although it is important at high-resolution, local measurements of surface roughness are not available in an operational setting. Thus, question was how often time-varying soil roughness information should be updated in operations for reasonable soil moisture retrievals but at effective computational cost. Local validations show that a monthly update for surface roughness is sufficient for soil moisture retrievals. In more details, Root Mean Square Errors (RMSE) of 0.01 m3/m3 is found at Yanco A3 site, and 0.03 m3/m3 at Yanco A5 site, with differences in backscattering between Integral Equation Model (IEM) simulation and Sentinel-1 measurement of 0.78 dB at Yanco A3 site and 0.012 dB at Yanco A5 site, respectively.