IMPACTS OF SOIL SURFACE ROUGHNESS CHANGES ON SMOS SOIL MOISTURE RETRIEVALS

The Soil Moisture Ocean Salinity (SMOS) soil moisture retrievals are too dry and noisy when compared to the South Fork of the Iowa River (SFIR), a heavily agricultural watershed with a USDA-ARS in situ soil moisture network. After testing for invalid retrievals, errors in auxiliary datasets, and a non-representative parameterization of scattering in the canopy, soil surface roughness changes were identified as the next potential source of the dry bias. Soil surface roughness increases the amount of radiation emitted from the surface; if the SMOS processor does not "know" that the soil is rough, the increased brightness temperature is interpreted as a drier soil. When the processor does account for a rougher soil surface, the previous dry bias between SMOS and the SFIR will reduce. This ability to zero the bias comes at a high cost: SMOS sensitivity to the SFIR soil moisture is halved between the moderately-rough and rough scenarios.