COMPARISON OF ALGORITHMS FOR RETRIEVAL OF SNOW WATER EQUIVALENT FROM NIMBUS-7 SMMR DATA IN FINLAND

The correlation between the brightness temperature of snow-covered terrain (dry snow) and the snow water equivalent in Finland was investigated using Nimbus-7 SMMR data. The satellite data set covers the winters of 1978-1979 through 1981-1982. The correlation analysis was performed for 17 different brightness temperature functions, each involving one or several frequencies and polarizations. In each case, the analysis was conducted separately for southern Finland (180 000 sq. km) and northern Finland (120 000 sq. km). The highest correlation coefficients between the satellite-derived brightness temperature functions and the mannally measured snow water equivalent values were obtained by using the brightness temperature difference between 37 GHz and either 18 GHz or 10.7 GHz, vertical polarization. In general, the microwave response to snow water equivalent was observed to be higher for northern Finland than for southern Finland, mainly due to larger forest cover fraction in southern Finland. By using the satellite-derived brightness temperature difference between 18 and 37 GHz for small test sites (about 10 000 sq. km), the correlation coefficient was observed to approach the values obtained from ground-based radiometer measurements. The accuracy of snow water equivalent retrieval from the 18 and 37-GHz SMMR data was estimated.