Denmark/Greenland/Faroe Islands: projects/activities

Monitoring climatological and hydrological parameters in a low arctic environment.

Ice sheet meltwater and sediment discharge is measured at only very few sites in Greenland. The measurements provide detailed insights into ice sheet surface melting, englacial meltwater routing, subglacial erosion, etc., and their importance increase with the lengthening of the time series. Monitoring was initiated by IGN (Copenhagen University) in 2006, and taken over by the Geological Survey of Denmark and Greenland in 2014. Data are available through the Programme for Monitoring of the Greenland Ice Sheet (www.PROMICE.dk).

Changes in surface reflection at the arctic tundra at Ny-Ålesund, Svalbard (79 N) were monitored during the melting season 2002 using a low cost multispectral digital camera with spectral channels similar to channels 2, 3, and 4 of the Landsat Thematic Mapper satellite sensor. The camera was placed 474 m above sea level at the Zeppelin Mountain Research Station and was programmed to take an image automatically every day at solar noon. To achieve areal consistency in the images (which is necessary for mapping purposes) the images were geometrically rectified into multispectral digital orthophotos. In contrast to satellite images with high spatial resolution the orthophotos provide data with high spatial and high temporal resolution at low cost. The study area covers approximately 2 km2 and when free of snow, it mainly consists of typical high arctic tundra with patchy vegetation and bare soil in between. The spectral information in the images was used to divide the rectified images into maps representing different surface classes (including three subclasses of snow). By combining classified image data and ground measurements of surface reflectance, a model to produce daily maps of surface albedo was developed. The model takes into account that snow-albedo decreases as the snow pack ages; and that the albedo decreases very rapidly when the snow pack is shallow enough (20-30 cm) to let surface reflectance get influenced by the underlying ground. Maps representing days with no image data (due to bad weather conditions) were derived using interpolation between pixels with equal geographical coordinates. The time series of modeled albedo-maps shows that the time it takes for the albedo to get from 80% to bare ground levels varies from less than 10 days in areas near the coast or in the Ny-Ålesund settlement till more than 70 days in areas with large snow accumulations. For the entire study area the mean length of the 2002 melting period was 28.3 days with a standard deviation of 15.1 days. Finally, the duration of the snowmelt season at a location where it is measured routinely, was calculated to 23 days, which is very close to what is the average for the last two decades.