Sensitivity to soil moisture of Capella X-band high-resolution SAR data over forests

Sensitivity to soil moisture of X-band high-resolution Synthetic Aperture Radar (SAR) data over the 10 openings between the trees in forests is evaluated. The VV backscattering coefficient is extracted 11 from a time-series of Capella images collected over two different regions across the United States. 12 In-situ soil moisture measurements recorded at fixed locations from the National Ecological 13 Observatory Network (NEON) are used as reference for the analysis. The geolocation uncertainty of 14 the original ground range detected Capella images at 0.8 m resolution was evaluated at 5 to 15 m. 15 Ground control points were used to improve geolocation accuracy to 1 to 5 m. Radar backscattering 16 and soil moisture exhibit linear correlation values up to 0.95, confirming the strong response of X17 band Capella to soil moisture changes when trees are not interfering with the scattering from the 18 thinly-vegetated soil over the openings. These findings reveal the potential for forest soil moisture 19 monitoring by micro-satellites offering meter-level high-resolution and agile tasking. Accordingly, 20 applications such as wildfire precursors, landslide prediction, and forest management may benefit as 21 long as the moisture conditions at the openings represent the soil moisture over larger areas.