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.