Global microwave land surface emissivity retrieval at the AMSR-E microwave frequencies

Land emissivity is a key boundary condition particularly when used in Numerical Weather Prediction (NWP) models. The objective of this study is to develop a global land emissivity product using AMSR-E passive microwave data. This work investigates the impact of the difference in penetration depths between passive microwave and thermal temperatures on the retrieval of land emissivity. AMSR-E frequencies (6.9, 10.7, 18.7, and 36.5 GHz) have been used to retrieve land emissivity. Composite clear sky skin temperature (DX) produced by the International Satellite Cloud Climatology Project (ISCCP) was used. Moreover, information on water vapor and air temperature obtained from the ISCCP database (TOVS data) was used to calculate the upwelling and the downwelling atmospheric brightness temperatures as well as the atmospheric transmission. Instantaneous land emissivity maps have been developed at different AMSR-E frequencies. 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. Also, a significant difference between ascending and descending overpasses emissivity was found in deserts and high topography regions.