Backscattering measurements of Alpine snowcovers at 5.3 and 35 GHz

This paper describes two network-analyzer (NA)-based scatterometers at 5.3 (C-band) and 35 GHz (Ka-band) as well as snowcover measurements made in the Swiss and Austrian Alps between December 1993 and January 1996. First, the setup and the mode of operation of the scatterometers are discussed. Both instruments measure the backscattering coefficients [Gamma] at hh, vv, vh, and vh polarizations and for incidence angles ranging from 0 to 70 [degrees]. The accuracy of 3 is generally better than [+ or -]1.8 dB, and the scatterometers are well suited for signature studies of natural surfaces. During the two years, we performed many backscattering measurements of natural, strongly layered snowcovers and we investigated relationships between [Gamma] and physical parameters of the snowcover. All measurements were collected in a signature catalogue. Here we report on results at 40 [degrees] incidence angle. We found that the combined use of active sensors at 5.3 and 35 GHz allows the discrimination of various snowcover situations, if multitemporal information is available. In addition, we observed a relationship of [Gamma] at 5.3 GHz with the integrated column height of liquid water and dependencies of [Gamma] at 35 GHz on the height of the dry snow, on the volumetric liquid water content at the snow surface, and on the thickness of the refrozen crust at the snow surface.