THE POTENTIAL OF TIMES SERIES OF C-BAND SAR DATA TO MONITOR DRY AND SHALLOW SNOW COVER

A study was conducted to assess tile potential of C-band synthetic ape rtuer radar (SAR) data to determine the snow water equivalent (SWE). A multitemporal (three winters) SAR data set was obtained using the Con vair-580 from the Canada Centre for Remote Sensing (CCRS) over a water shed in the Appalachian Mountains in southern Quebec, Canada, The SAR data were relatively calibrated using extended targets (coniferous sta nds), Extensive ground measurements were done simultaneously to each o f the seven flights, in order to measure the snow covet-characteristic s (depth, density, SWE, liquid water content, temperature, and dielect ric profiles) as well as the soil characteristics (moisture, temperatu re), To Estimate the SWE of a given snowpack, a model which links the scattering coefficient to the physical parameters of the snow cover an d the underlying soil has been developed. The model is based on the ra tio of the scattering coefficient of a field severed by snow to the sc attering coefficient of a field without snow, The analysis has reveale d that volume scattering from a shallow dry snow cover (SWE < 20 cm) i s undetectable, The backscattering power is dominated by foil surface scattering, the latter varying with the decrease of liquid water conte nt in the surface layer with decreasing soil temperature below 0 degre es C, Then, the scattering ratio decreases proportionally to the diele ctric constant of the soil in winter, Furthermore, a unique relationsh ip for three acquisition dates has been found between the thermal resi stance, R, of the snow pack and the backscattering power ratio, Then, the spatial distribution of the power ratio should depict the spatial distribution of R, givers spatially uniform climatological conditions over the study area. Since linear relationships between SWE and R have been observed, it should be possible to estimate the SWE of shallow d ry snow cover with C-band SAR data using few ground truthing data in a n open area when the soil is frozen, A follow-up of this study would b e to test if the SWE-R ratio relationship could be generalized. Prelim inary results show that a similar relationship can also be obtained wi th ERS-1 data on another test area.