Retrieval of snow water equivalent using passive microwave brightness temperature data

Existing algorithms for retrieving snow water equivalent (SWE) from the Spe cial Sensor Microwave/Imager (SSM/I) passive microwave brightness temperatu re data were assessed and new algorithms that include physiographic and atm ospheric data were developed for the Red River basin of North Dakota and Mi nnesota. The frequencies of SSM/I data used are 19 GHz and 37 GHz in both h orizontal and vertical polarization. Encouraging calibration results are ob tained for the algorithms using multivariate regression technique and dry s now cases of the 1989 and 1988 SSM/I data (from DMSP-F8). Similarly, valida tion results for data not used in calibration [e.g., 1988 (1989 as calibrat ion data), 1989 (1988 as calibration data), and 1997 (from DMSP-F10 and F13 )] are also encouraging. The nonparametric, Projection Pursuit Regression ( PPR) technique also gave good results in both stages. However, for the vali dation stage, adding a shift parameter to all retrieval algorithms was alwa ys necessary, possibly because of different scatter-induced darkening (caus ed by scattering albedo), which could arise even for snowpacks of the same thickness because snowpacks undergo different metamorphism in different win ter years. Screening criteria are also proposed to eliminate SSM/I footprin ts affected by large water bodies and depth-hoar-another key step toward re liable SWE estimation from passive microwave data. (C) 2000 Elsevier Scienc e Inc.