Effective snow cover by VIS/IR radiometry

The main operational characteristics are here highlighted:

• Coverage: Northern Hemisphere
• Cycle: Daily
• Resolution: 0.01-degree
• Timeliness: 6 hours
• Formats: GRIB2

Product ESC-H (Effective snow cover by VIS/IR radiometry) is based on multi-channel analysis of the AVHRR instrument onboard MetOp satellites. The AVHRR radiometer has an IFOV of 1.1 x 1.1 km² at nadir degrading to ∼ 2 x 6 km² at the edge of the 2900 km cross-track swath. Computing fractional cover would in principle require segmenting the image in arrays of pixels (typically ∼ 32 x 32) and counting those classifies as snow. This would lead to unacceptable product resolution. For H SAF, fractional cover is generated at pixel resolution, by exploiting the brightness intensity that is the convolution of the snow signal (highest) and the fraction of snow within the pixel (“effective cover”). The retrieval algorithm is somewhat different for flat/forested area and for mountainous regions. ESC-H is generated in Finland by FMI and in Turkey by TSMS. The products from FMI and from TSMS both cover Northern Hemisphere, but thereafter are merged at FMI by blending the information on flat/forested areas from the FMI product and that one on mountainous areas from the TSMS product. The observing cycle of the complex of MetOp satellites over Europe is about 3 h. For a single satellite pass, several areas in the scene would provide no useful measurements because of clouds. Therefore, the complex of passes is multi-temporally analysed to search for time instants of cloud-free conditions in a given time interval (e.g., 24 h). However, since short-wave channels play an essential role in the retrieval algorithm, the useful range of hours is in daylight. For more information, please refer to the Products User Manual (PUM-35).