Estimation of snow water equivalent using passive microwave radiation data

Abstract

The principal objective of this study was to analyze, through regression modelling, the degree to which passive microwave radiation can be used to interpret snow water equivalent. The methodology reflects the importance of isolating phenomena other than snow water equivalent which may influence the microwave signal. These factors include: snow wetness; depth hoar; complex mountainous terrain; dense forest cover; and atmospheric precipitable water. It is shown that for a non-forested, non-mountainous terrain, the snow water equivalent of a pack with no depth hoar and no melting snow can be estimated with 95 percent confidence within plus or minus 44 mm. This error doubles when there is depth hoar present, and the relationship between snow water equivalent and brightness temperature reverses, as the scattering is greatest in shallow snowpacks with large depth hoar crystals. Significant results are obtained for melting snow conditions, despite theory indicating the contrary, by using only the night-time satellite passes. Dense forest cover impacts the microwave signal but appears not to completely mask the influence of the underlying snowpack. Lastly, it is difficult to collect ground data in regions of complex mountainous terrain which accurately represent snow conditions over a large area. However, some information can be obtained using high elevation SNOTEL sites from the Rocky Mountains.