Scaling information for scatterometer derived soil moisture
estimates

Abstract: 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 are often requested. Current remote
sensing methods are limited to a spatial 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.