| Considerable seasonal and inter-annual variation in the physical properties and extent of snow cover pose problems for obtaining reliable estimates of quantities and characteristics of snow cover from both conventional and satellite measurements (Goodison and Walker, 1994; Goita et al., 2003). In spite of these challenges, the Climate Research Branch of the Meteorological Service of Canada (MSC) has developed a suite of algorithms to derive snow water equivalent (SWE) estimates from remotely sensed passive microwave imagery (Goodison and Walker, 1994; Derksen et al., 2002a; Goita et al., 2003). The MSC algorithms work particularly well over open prairie environments under the assumption of large areas of consistent snow cover (Derksen et al., 2002a). While studies have documented underestimation in passive microwave estimates of snow extent in marginal areas when compared to optical satellite data (Derksen et al., 2003b), the accuracy in SWE retrievals under variable and patchy snow conditions is not well understood.;This research verifies that the continuous snow cover assumption embedded in the MSC passive microwave SWE algorithm does not produce acceptable results over a patchy snow cover. Several in-situ observations that appear to play an important role in affecting the satellite passive microwave data over a variable snow cover include the presence or absence of an ice lens, the fractional snow covered area, snow depth and the ground temperature. In an attempt to mitigate the impact of fractional snow cover on snow water equivalent estimates, a weighted algorithm is proposed that applies the percentage of snow cover over a remotely sensed footprint to the SWE estimate derived by the MSC algorithm.;In an effort to better understand how a variable and patchy snow cover impacts remotely sensed SWE retrievals, field-based experiments were conducted over patchy snow covered areas in February 2005 and March 2008. A systematic sampling strategy was developed over a 1600 square kilometre (km2 ) area in southern Saskatchewan near a calibration/validation flight line used for algorithm development in the 1980s (Goodison and Walker, 1994). Land covers found at the sampling sites included fallow and stubble fields, pastures and shelter belts. A large number of sampling sites contained snow pack layers that included one or more ice lenses. |
