Determination of snow water equivalent using RADARSAT SAR data in eastern Canada

In the 1998-1999 winter, the operational feasibility of using RADARSAT SAR data to estimate the spatial distribution of snow water equivalent (SWE) in a large hydroelectric complex managed by Hydro-Quebec (La Grande River wat ershed) has been successfully demonstrated. This watershed is located in th e subarctic climatic region in the north-west of the Quebec province. The v egetation consists of moderately dense to open Black Spruce forests, open l ands, burned lands and peat bogs. In the last few years, an original approa ch well adapted for this region has been developed to estimate the SWE from SAR data (ERS-1, RADARSAT). This approach is based on the fact that the sn ow cover characteristics influence the underlying soil temperature which in fluences the dielectric properties of the soil and then the recorded backsc attering signal. Then, a linear relationship between the backscattering rat ios of a winter image and a snow-free (fall) image, and the snowpack therma l resistance (thermal insulation properties) has been established. Conseque ntly, the algorithm infers the SWE from the estimated thermal resistance an d the measured mean density of the snowpack. This algorithm has been implem ented within a MapInfo(TM) application that has been named EQeau. It allows mapping of the spatial distribution of the estimated SWE at the desired le vel (pixel, square grid, sub-watershed). During the 1998-1999 winter, EQeau has been used successfully in a pre-operational mode using calibrated Wide beam images (W1) from RADARSAT. The algorithm has given mean estimated SWE values similar to the SWE values derived from Hydro-Quebec snow transects (relative difference between 1% and 13%). Also, the SWE increase measured f rom January to March 1999 is clearly detected on the maps covering almost 7 7 000 km(2) The next steps will be the evaluation of the ScanSAR images and the demonstration of the economical advantages of using RADARSAT data in a hydrological forecasting system. Copyright (C) 1999 John Wiley & Sons, Ltd .