SPECTRAL, SPATIAL AND TEMPORAL CHARACTERISTICS OF ARCTIC TUNDRA REFLECTANCE

The objective was to quantify and analyse the spectral, spatial and temporal variability of solar radiation reflected from arctic tundra vegetation at a study site in the Brooks Range foothills of northern Alaska. Spectral radiance data from hand-held radiometers and the SPOT HRV sensor were sampled along hillslope transects (toposequences) and within four vegetation community types. The spatial trend of normalised difference vegetation index (NDVI) along the toposequences corresponded to variations in the abundance of green vegetation matter and in vegetation composition. A marked temporal increase in the NDVI occurred along the toposequences from the beginning of the growing season (mid-June) to peak green up (end of July). The spectral signatures of three tundra dominant vegetation communities, dry heath, moist tussock and wet sedge, were moderately separable, with dry heath being most separable. The overall separability of the major community types was similar at all times during the growing season, with the most divergent signatures occurring in late July during maximum greenness. Some of the important ecological features of the arctic tundra landscape are not resolved by the SPOT HRV sensor in multi-spectral mode, in spite of its high (20 m) spatial resolution.