Preliminary analysis of snow microwave radiometry using the SSM/I passive-microwave data: the case of La Grande River watershed (Quebec)

Abstract

The general objective of this paper is to estimate the snow water equivalent (SWE) of the La Grande River watershed (northern Quebec), using passive-microwave data from the SSM/I sensor. Particular emphasis is placed on the analysis of SSM/I multitemporal variations.The analysis of a database containing observations for three winters shows that the brightness temperatures of the snow decrease as the SWE increases for shallow snow covers. However, when the SWE is >180–200 mm, the relationship reverses. This is directly linked to the fraction of large snow crystals in the snow cover, since these are responsible for most of the volume scattering. The snow emissivity is lower for shallow snow covers, since the higher temperature gradient is responsible for the quick formation of large snow crystals. For SWE >80–200 mm, the temperature gradient decreases and large crystal formation is minimal. Since volume scattering is lower, snow emissivity tends to increase. The observations confirm what was observed by Mätzler and others (1982) and Mätzler (1994).Two regression lines were used to estimate the SWE for the beginning and the end of winter. This approach appears to be better, since it takes into account the structure of snow cover. The results were used to derive representative maps of the SWE.