Automatic snow cover monitoring at high temporal and spatial resolution, using images taken by a standard digital camera
The inter- and intra-annual snow cover distribution in the Zackenbergdalen valley, north-east Greenland, was monitored using images from a digital camera. The Digital Camera Images (DCIs) provide-in contrast to satellite images-data with a high temporal and spatial resolution at low cost. The digital camera, positioned on a rock 500 m above sea level (asl), automatically takes oblique photographs of the valley. To obtain the necessary area consistency for mapping purposes, the DCIs are transformed into digital orthophotos. Snow cover mapping is performed using these orthophotos. In order to suppress errors due to illumination effects, a normalized index based on red, green and blue (RGB) values was developed. The index can be used as an analogue to the Normalized Difference Snow Index (NDSI), commonly used in combination with Landsat Thematic Mapper (TM) images. During the melt-off season, a maximum of 10-15 Landsat TM passes occur over the Zackenberg area. For the 1999 meltoff season only three cloud-free TM images were usable for snow-mapping, while 46 DCIs were suitable for this purpose. Analysis of 1998 and 1999 data shows that the snow cover in Zackenbergdalen decreases gradually during the melt-off season. The resulting depletion curves have a 'laterally reversed S-shaped' form, which depends on the initial amount of snow in the area, the temperature during the melt-off season and altitudinal level.