Using global land surface emissivity as soil moisture indicator

Soil moisture is one of the most uncertain variables in hydrologic models, especially in large watersheds. Direct measurement of this parameter at these large scales is not straightforward. The main objective of this work is to demonstrate the potential of using land microwave emissivity as a surrogate for soil moisture. First, an instantaneous global microwave land emissivity product has been developed using AMSR-E observations. This retrieval utilizes all AMSR-E frequencies and infrared-based data for physical skin temperature. Data sets provided by the International Satellite Cloud Climatology Project (ISCCP) were used. Moreover, information on water vapour and air temperature obtained from the ISCCP database (TOVS data) was used to calculate the upwelling and downwelling atmospheric brightness temperatures, as well as the atmospheric transmission. A monthly composited map was developed for each frequency. The analysis of the obtained maps has shown an acceptable agreement with the global pattern of land use/land cover. The difference between V and H polarization, as well as the difference between day and night in emissivity retrievals, showed an acceptable consistency with soil moisture. Fraction of surface water was developed in global scale using land surface emissivity with reasonable agreement with soil moisture except in highly vegetated area.