Evaluation of a multi-algorithm approach to passive microwave monitoring of Central North American snow water equivalent

The Meteorological Service of Canada (MSC) has developed a series of operational snow water equivalent (SWE) retrieval algorithms for central Canada, based on the vertically polarized difference index for the 19 and 37 GHz channels of the Special Sensor Microwave/Imager (SSM/I). Separate algorithms derive SWE for open environments, deciduous, coniferous, and sparse forest cover, with the final SWE value representing the area weighted average based on the proportional land cover within each pixel. In this study, 5-day averaged (pentad) passive microwave derived SWE imagery for the winter season (December, January, February) of 1994/95 is compared to a network of in situ SWE measurements throughout central Canada in order to assess algorithm performance. Results indicate that retrieved SWE remains within ±10-20 mm of surface observations, independent of fractional within-pixel land cover. No bias towards under or over-estimation is evident except in high-density coniferous regions where the MSC algorithm consistently underestimates SWE relative to the surface measurements. Algorithm performance is notably improved when compared to a previously developed MSC algorithm that does not consider land cover and consistently underestimates SWE in forested areas