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 /spl gamma/ at hh, /spl nu//spl nu/, /spl nu/h, and /spl nu/h polarizations and for incidence angles ranging from 0 to 70/spl deg/. The accuracy of /spl gamma/ is generally better than /spl plusmn/1.8 dB, and the scatterometers are well suited for signature studies of natural surfaces. During the two years, the authors performed many backscattering measurements of natural, strongly layered snowcovers and the authors investigated relationships between /spl gamma/ and physical parameters of the snowcover. All measurements were collected in a signature catalogue. They report on results at 40/spl deg/ incidence angle. They 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, they observed a relationship of /spl gamma/ at 5.3 GHz with the integrated column height of liquid water and dependencies of /spl 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.