Improving satellite soil moisture estimates by combining passive and active microwave observations (1992-2008).

We propose a methodology to blend soil moisture retrievals from passive (SSM/I, TRMM and AMSRE) and active (ERS and ASCAT) microwave satellite observations and obtain an improved long-term (1992– 2008) global product. The first step is to merge the three passive microwave data sets into a single “passive” product and two active microwave data sets into a single “active” product. This avoids the issue of differences in sensor specifications resulting in different absolute soil moisture values. Next, both data sets are adjusted against a common reference (GLDAS-Noah), which scales both data sets to the same dynamic range and allows the generation of a blended product. The proposed approach has the potential to be applied to existing as well as new missions.

Spatial coverage by passive (dark grey), active (light grey) microwave or both (medium grey) in the merged product. Tropical rain forests were masked out due to the high vegetation density.