Comparison between the Results of a Snow Metamorphism Model and Remote Sensing Derived Snow Parameters in the Alps

The numerical snow metamorphism model CROCUS derives a complete description of the snow cover according to its geographical location (range), elevation, slope, and orientation. From the remote sensing data, snow parameters that were comparable to the model results were derived: the lower elevation of the snow cover, the surface grain size, and the surface temperature. The Landsat Thematic Mapper sensor was used because it has a good spatial resolution, a short wave infrared channel which is sensitive to grain size, and a thermal infrared channel. A first Landsat TM (Thematic Mapper) scene was acquired on 24 April 1992 and a second one on 11 December 1992. A DEM (digital elevation model) was used to obtain the local incidence angles and the elevation of each snow pixel. The pixels were then grouped according to the CROCUS classification (range, elevation, slope, orientation), and the mean snow characteristics for each class were compared with the CROCUS results. The lower limit of snow and the surface grain size derived from TM data compared favorably with the model results even if those parameters were not always easy to define. Larger differences were found for the temperature because it varies rapidly and is very sensitive to shadowing by surrounding mountains and also because its remote measurement is dependent on atmospheric conditions.