Impact of Calibration Error of Microwave Brightness Temperatures on Soil Moisture Retrievals

Soil moisture (SM) is one of the most important land surface hydrospheric state variables. Several satellite missions designated for or with capability of soil moisture observation have been planned. Among them are the L-band microwave Soil Moisture and Ocean Salinity (SMOS) mission by European Space Agency (ESA) and the Soil Moisture Active/Passive Mission (SMAP) by NASA. The C/X –band Advanced Microwave Scanning Radiometer (AMSR2) is planned for the GCOM-W mission of Japan Aerospace Exploration Agency (JAXA) and a C/X-band Microwave Imager Sounder (MIS) for the National Polar-orbiting Operational Environmental Satellite System (NPOESS) satellites. The China Meteorological Administration (CMA) will a Microwave Radiometer Imager (MWRI) on each of their Fengyun-3 satellites. Researches on remotely sensing SM with the C/X and L-band microwave sensors has lead to several successful soil moisture retrieval algorithms. However, various uncertainties associated with the microwave brightness temperature (TB) observations have limited the retrieval accuracies. These uncertainties include absolute accuracy of the TBs and how the relative accuracy of different polarizations impacts the retrieval? In this study, an observing system simulation experiment is conducted using the Noah land surface model (LSM) and a Land Low-frequency Microwave Emission Model (LLMEM). The H- and V-pol TBs are simulated with the LLMEM from the Noah LSM output. Various Gaussian errors are then added to the TBs. Several published algorithms are then used to retrieve soil moisture for each preset level of the Gaussian errors. Analyses on how the algorithms perform for each Gaussian error level reveal their sensitivities to TB calibration errors.