Intercomparison of Surface Roughness Parameterizations for Soil Moisture Retrieval

Soil moisture plays a key role in many hydrological and agricultural processes because it controls the water and heat energy exchange between the earth and the atmosphere. Addressing the need for routine global surface soil moisture maps, the European Space Agency (ESA) launched the Soil Moisture and Ocean Salinity (SMOS) mission in 2009. It provides L-band microwave brightness temperature observations in dual polarization with multi-incidence angles [1]. Scheduled for launch in 2014, the National Aeronautics and Space Administration (NASA) is developing the Soil Moisture Active Passive (SMAP) mission which will deploy a combined radar and radiometer instrument to improve soil moisture retrieval capabilities and spatial resolution [2]. Both the SMOS and the SMAP missions use the tau-omega model as the key algorithm for passive microwave soil moisture retrieval. This model has been used in numerous L-band studies for soil moisture retrieval at different scales throughout Europe, America and Australia (eg. [3, 4]). However, the surface roughness parameterization of this model remains an unresolved issue and is often considered a tuning variable. Consequently, this paper tests the current roughness parameterizations with independent field data.