Assessment of Soil Moisture Information Content in Level-1 Data from Low-Frequency Active and Passive Microwave Sensors

Low-frequency microwave brightness temperature and backscatter observations are sensitive to surface soil moisture, a key variable for applications like numerical weather prediction, drought monitoring and climate modeling. With ESA's Soil Moisture and Ocean Salinity (SMOS) mission and NASA's Soil Moisture Active Passive (SMAP) mission, two L-band radiometers dedicated to soil moisture monitoring are currently in orbit. In addition, operational soil moisture products exist based on EUMETSAT MetOp C-band advanced scatterometer (ASCAT) and JAXA GCOM-W multifrequency radiometer (AMSR2) data. This study aims to assess the information content of Level-l data from active and passive microwave sensors for soil moisture estimation. Specific focus lies on the comparison between frequencies (L-band, C-band, X-band) and sensor types (active and passive) as well as the added value of multi-angular brightness temperature observations (e.g. from SMOS) with respect to fixed incidence angle observations. The study will provide insights into the suitability of different sensor types for soil moisture estimation irrespective of the individual Level-2 retrieval algorithm specifics. The results shall assist the definition of new observation concepts and the identification of synergies between planned or existing satellite missions.