Utilizing satellite snow cover data for climatological analysis: a comparison of passive microwave and optically derived time series, 1978 - 1995

When Special Sensor Microwave/Imager (SSM/I) and Scanning Multichannel Microwave Radiometer (SMMR) data are combined, the time series of spaceborne passive microwave brightness temperatures extends from 1978 to the present. The Meteorological Service of Canada (MSC) has developed a series of operational snow water equivalent (SWE) retrieval algorithms for western Canada that can be applied to both SMMR and SSM/I data. Before research issues can be addressed with a cross-platform time series, however, attention must be given to the impact of spatial, temporal, and radiometric differences between the SMMR and SSM/I data on time series continuity and consistency. In this study, we illustrate that passive microwave SWE retrievals with the MSC algorithms during the nine SMMR winter seasons (1978 - 1987) are consistently lower than the SWE estimates produced for the following eight SSM/I winter seasons (1987 - 1995). A snow extent anomaly time series produced by the National Oceanic and Atmospheric Administration (NOAA) from optical satellite data shows that the SMMR seasons of 1978/79 through 1986/87 are not characterized by deficit snow cover when compared to the SSM/I seasons of 1987/88 through 1994/95, indicating a consistency problem in the cross-platform passive microwave time series. Previously derived empirical brightness temperature corrections are examined, but appear to be unsuitable for use with the MSC algorithms.