Effective snow cover by VIS/NIR of AVHRR - Metop

The combined effect, within a product resolution element, of fractional snow cover and other reflective contributors is used to estimate the fractional cover at resolution element level. The product may be processed in different ways and have different quality depending on the surface being flat, forested or mountainous. The algorithm is based on multi-channel analysis of AVHRR, the most important being those in shortwave, thus the product is generated in daylight. The “deficit” of brightness in respect of the maximum one is correlated to the lack of snow in the product resolution element. In the case of forests, the expected maximum brightness (or the “transmissivity”) is evaluated in advance by a high-resolution instrument (MODIS). In order to search for cloud-free pixels, multi-temporal analysis is performed over all images available in 24 hours (in daylight).