A regional snow-line method for estimating snow cover from MODIS during cloud cover

The objective of this study is to propose and evaluate a method for snow cover mapping during clouds using the daily MODIS/Terra snow cover product. The proposed SNOWL approach is based on reclassifying pixels assigned as clouds to snow or land according to their relative position to the regional snow-line elevation. The accuracy of the SNOWL approach is evaluated over Austria, using daily snow depth measurements at 754 climate stations and daily MODIS/Terra images in the period July 2002-December 2005. The results indicate that the SNOWL method provides a robust snow cover mapping over the entire region even if the MODIS/Terra cloud cover is as large as 90%. Cloudiness is decreased from 60% (MODIS/Terra) to 10% (SNOWL) without hardly any change in mapping accuracy. Sensitivity analyses indicate that the estimation of the regional snow-line elevation is particularly sensitive to the misclassification of cirrus clouds as snow in the period between May and October.