While most Americans think of reindeer only in conjunction with holiday joy, the real animals and their herders live in the Arctic year-round and are experiencing global warming’s serious effects on snow cover and migration patterns.To help remedy this situation, scientists backed by the European Space Agency (ESA) have undertaken an initiative called Polar View to provide the herders with satellite-based snow maps. Although it is not yet known to what extent the maps will assist the herders (Researchers hope that a future meeting with them will provide more insight), one important benefit is clear. During the spring, when the herds migrate to their summer pastures, the maps can help the herders direct the reindeer to areas where the snow cover is deeper. This prevents the animals from stopping continually to feed on lichen, prolonging their migration and causing problems for the herders. Scientists at the Northern Research Institute in Tromsø and at the Norwegian Computing Center in Oslo, both in Norway, have developed algorithms to extract fractional snow cover data from satellite images. They use data gathered over the course of seven days to create a map that displays the snow cover currently on the ground in the Scandinavian mountain region (Norway and western Sweden), with each pixel covering an area of 250 × 250 m. Comparing their snow measurements with the descriptions provided by herders in the various locales, the scientists can improve the map legend and develop an even more accurate snow map.A multisensor, multitemporal snow map, created using satellite information, shows the varying snow depths in a region of Scandinavia. Green areas indicate there is no snow cover, yellow shows sections no information is available for, and the varying shades of white represent the depth of the snow. Image courtesy of Richard Hall, Kongsberg Satellite Services.The investigators are using data from two satellites: ESA’s Envisat, which provides synthetic aperture radar images in wide-swath mode, and NASA’s Modis, which provides optical images at 250-m resolution. These two satellites were chosen because they cover the area of interest, and their data is free to the researchers.The mapping process, beginning with the algorithm design, has been under development for many years. A reference data set had to be collected, specifically during the summer season to yield a baseline for the lowest snow levels in the area. Other features that could affect snow measurement – such as the locations of lakes, glaciers, forest and open ground – also were mapped to make the final product as accurate as possible.The team plans to extend its coverage to northern Russia, which is also home to reindeer and their herders.