Scaling information from ENVISAT ASAR data for downscaling of scatterometer derived soil moisture estimates to 1 km resolution

Soil moisture information is an important factor in the fields of hydrology, meteorology and climatology. For hydrological applications, soil moisture data with a spatial resolution of 1 km is often requested. Current remote sensing methods are limited to a spacial resolution of 25–50 km. This study was motivated by the need to improve the resolution of soil moisture information. The aim was to produce and make a first evaluation of scaling information that could be used for validating spatial downscaling of scatterometer derived soil moisture information to achieve a resolution of 1 km. The backscatter intensity from surface scattering is largely determined by the moisture content in the upper few centimetres of the soil. Based on the assumption that soil moisture is mainly driven by large scale atmospheric forcing, the local and regional soil moisture content is likely to be well correlated. Therefore, also the backscatter intensity on the two scales is expected to show similar scaling properties. By using time series of ENVISAT ASAR data, a measure of the temporal correlation between the backscatter intensities on the two scales can be calculated. For locations where a high temporal correlation is achieved, the regional soil moisture estimates can be used directly on the 1 km scale. Scaling information for a large part of the African continent was produced and the influence of land cover was analysed. It is concluded that there is a high potential for downscaling scatterometer derived soil moisture information for agricultural regions, including cropland and pasture, and over range land, which includes savannas and land covered with grass or shrub.