Black and White-Sky Albedo Values of Snow: In Situ Relationships for AVHRR-Based Estimation Using CLARA-A2 SAL

Abstract

The relationship of black-sky and white-sky albedo values of snow-covered terrain is studied using empirical measurements of six BSRN sites and the Finnish Meteorological Institute Sodankylä site, where albedo measurements are carried out both in an open area and above coniferous forest. In addition, a forest model was used to provide simulated albedo values to cover a wider leaf area index range. Linear regression formulas for estimating the monthly mean white-sky albedo value on the basis of the monthly statistics of the black-sky albedo were derived separately for open and forested areas. The statistical parameters used were the mean, median, standard deviation, skewness and kurtosis. In addition, the monthly mean solar zenith angle value was used as well. The mean absolute difference between the estimated monthly mean white-sky albedo and the empirical value was 0.027 for open areas and 0.015 for forested areas. The derived formulas were applied to the satellite black-sky albedo product CLARA-A2 SAL to generate white-sky albedo maps. Using the open snow area regression for the sea ice area produced values comparable to measured values both around the Antarctic and in the Arctic sea ice area.