I. Introduction
Microwave radiometry of land should carefully account for large-scale relief effects when applied to hilly or mountainous areas [1], which represent important targets within earth remote sensing from satellites, particularly for hydrological purposes. Indeed, variations in topography influence the upwelling brightness temperature measured by a satellite radiometer in several ways. The optical depth of the atmosphere is modified, the radiometer observation angle becomes a function of the surface slope, parts of the scene may be shadowed, radiation can be reflected from one tilted surface to another, and a depolarization effect occurs. Moreover, at microwave frequencies, the large variability of the mountainous scenario should be considered, if compared with the relatively large antenna footprint [2].