Passive microwave soil moisture downscaling using evaporative fraction

This paper develops two different approaches for downscaling (disaggregation) passive microwave derived soil moisture from coarse resolution L-band observations. Ground and airborne data collected over Walnut Gulch experimental watershed during the Monsoon ’90 experiment were used to test these approaches. These data consisted of eight micrometeorological stations (METFLUX) and six flights of the L-band Push Broom Microwave Radiometer (PBMR). For each PBMR flight, the 180m resolution L-band pixels covering the eight METFLUX sites were first aggregated to generate a 500m “coarse-scale” passive microwave pixel. The coarse-scale derived soil moisture is then downscaled to 180m resolution using two different surface soil moisture indices (SMIs): i) the evaporative fraction (EF), which is the ratio of the evapotranspiration to the total energy available at the surface; and ii) the actual evaporative fraction (AEF), defined as the ratio of the actual to potential evapotranspiration. It is