High-Resolution Soil Moisture Retrieval With ASCAT

Satelliteborne C-band scatterometer measurements of the radar backscatter coefficient $(\sigma^{0})$ of the Earth can be used to estimate soil moisture levels over land. Such estimates are currently produced at 25- and 50-km resolution using the Advanced Scatterometer (ASCAT) sensor and a change detection algorithm originally developed at the Vienna University of Technology (TU-Wien). Using the ASCAT spatial response function (SRF), high-resolution (approximately 15-20 km per pixel) images of $\sigma^{0}$ can be produced, enabling the creation of a high-resolution soil moisture product using a modified version of the TU-Wien algorithm. The high-resolution soil moisture images are compared to images produced with the Water Retrieval Package 5.5 algorithm, which is also based on the TU-Wien algorithm, and to in situ measurements from the National Oceanic and Atmospheric Administration U.S. Climate Reference Network (NOAA CRN). The WARP 5.5 and high-resolution image products generally show good agreement with each other; the high-resolution estimates appear to resolve soil moisture features at a finer scale and demonstrate a tendency toward greater moisture values in some areas. When compared to volumetric soil moisture measurements from NOAA CRN stations for 2010 and 2011, the WARP 5.5 and high-resolution soil moisture estimates perform similarly, with both having a root-mean-square difference from the in situ data of approximately 0.06 m3/m3 in one study area and 0.09 m3/m3 in another.