Development of a cross-platform (SMMR and SSM/I) passive microwave derived snow water equivalent dataset for climatological applications

When Special Sensor Microwave/Imager (SSM/I; in operation 1987 to present) and Scanning Multichannel Microwave Radiometer (SMMR; 1978-1987) data are combined, the time series of dual polarized, multichannel, spaceborne passive microwave brightness temperatures extends from 1978 to the present. The Meteorological Service of Canada (MSC) has developed operational snow water equivalent (SWE) retrieval algorithms for western North America that can be applied to both SMMR and SSM/I data. Evaluation of this cross-platform time series shows that SWE estimates derived during SMMR winter seasons are systematically and significantly lower than retrievals during SSM/I seasons if no brightness temperature adjustments are employed. An examination of co-located brightness temperatures over terrestrial surfaces of central North America during the SMMR and SSM/I overlap period of August 1987 show that SSM/I brightness temperatures systematically exceed SMMR measurements, with the magnitude of this difference dependant on overpass time and brightness temperature magnitude. Regression relationships were determined using data from the overlap period, and utilized to adjust midlatitude terrestrial SMMR data to an SSM/I F-8 baseline. A SWE time series was subsequently reprocessed using these adjusted SMMR brightness temperatures. The resulting SWE dataset produces a time series of acceptable cross-platform homogeneity when assessed with in situ SWE measurements and remotely sensed snow extent data. Climatological research questions that demand a time series of significant length can now be confidently addressed with this passive microwave derived dataset.