Retrieval of regional Snow Water Equivalent from space-borne passive microwave observations

The feasibility of space-borne microwave radiometers for monitoring the evolution of snow cover in a drainage area is investigated. Four winter sets (1993/94, 1995/96, 1996/97, 1997/98) of SSM/I radiometer observations for the 51,000 km(2) River Kemijoki drainage area, Northern Finland, are used for analyses. The Snow Water Equivalent (SWE) of dry snow cover is estimated by employing the Helsinki University of Technology (HUT) Snow Emission Model-based automatic inversion algorithm. For comparison, the SWE estimates are also determined by using a conventional empirical Spectral and Polarization Difference algorithm. The results indicate that the HUT Snow Emission Model-based automatic algorithm can estimate the regional SWE under dry snow conditions with an overall RMSE of about 30 mm without using any training reference data on SWE (e.g., in situ reference values). The retrieval error was found to vary considerably from year to year. At best, the annual SWE retrieval RMSE showed values as low as 20 mm. (C) Elsevier Science Inc., 2001.