Impact of topography on microwave emissivity retrieval from satellite radiometers

A simulation study to understand the influence of the topography on the land emissivity estimated by a satellite microwave radiometer is accomplished in this work. A mountainous area in the Alps (Northern Italy) is considered and the information on the relief, extracted from a digital elevation model (DEM), is exploited. We have simulated an observation of the area of interest performed by a satellite radiometer flying at 800 km of altitude and conically scanning the area with an angle of 53deg. We have considered the following frequencies: 23.8, 36.5 and 90.0 GHz, with the following spatial resolutions: 60times40, 37times29 and 15times13 km for the, 23-, 36-, and 90-GHz bands, respectively. The results indicate that the effect of the topography tends to lower the antenna temperature, thus implying an underestimation of the surface emissivity. This effect is larger at 90 GHz for which the maximum underestimation of the antenna temperature is in the order of 5 K.