Simulating Topographic Effects on Spaceborne Radiometric Observations Between L and X Frequency Bands

A numerical simulator of satellite microwave-radiometric observations of orographically complex scenes, at various frequencies and observation angles, has been developed. The Simulator of Topographic Artefacts in MIcrowave RAdiometry (STAMIRA) exploits the information on the relief, extracted from a digital elevation model, and has been applied to a test case concerning a mountainous area in the Alps by assuming a simplified land-cover scenario consisting of bare terrain with two kinds of roughness (smooth and rough soils). The 1-10-GHz range has been considered to determine scattering and emission of soil and a nonscattering atmosphere has been supposed. The simulations have shown the large impact of the rotation of the polarization plane and of the brightness-temperature enhancement occurring for facets illuminated by radiation from the surrounding elevated terrain with respect to flat surfaces which scatter atmospheric downward radiation only. By considering also the antenna-pattern integration and the dependence of surface emissivity on the local observation angle, we have found that, for our case study, the brightness temperature is larger than that measured observing a flat terrain at horizontal polarization. At vertical polarization, the opposite occurs. These differences are analyzed and quantified.