Snow Cover Maps from Satellite

Total snow cover for mainland Norway

This figure shows the ratio of snow-covered area for mainland Norway for the most recent years. The figure is derived using data from satellite-based snow cover maps. Dark gray areas indicate the time of year for which the snow cover maps due to low solar elevation / polar night do not have full coverage for mainland Norway.

Latest snow cover map

The snow cover map is based on data from multiple satellite swaths. Grey areas show regions that are cloud-covered for all satellite swaths for this day. Note that the map contains land information only. Some water areas will typically be covered by sea ice / lake ice for parts of the year without this showing in this map.

 

Background

It is not always straight forward to separate cloud and snow in a satellite image. Cloud and snow reflect sunlight fairly equally at visible wave lengths, and can therefore appear very similar (see example below, left image labeled "RGB124"). We exploit that cloud and snow reflect differently at larger wavelengths (middle image labeled "RGB264"). Here, snow and cloud are easier to seperate as snow takes on a pink color, while clouds appear mostly in white/blue. The right panel shows the corresponding satellite product for this satellite swath. Red color indicates snow covered areas, while blue indicates areas that mostly likely are snow free.

The example above is a section of a MetOp-1 swath from February 24th 2017, 08:45 UTC.

Several of these swath products are combined into daily snow cover maps. The image below shows a snow cover map from the same day as the example above. Here, white shows snow, green corresponds to snow free, and blue shows ocean. The grey areas show cloud cover. If using optical satellite data only we cannot know wheter there is snow or snow free land below the cloud cover.