Nadir and bidirectional surface measurements of Arctic tundra: site differentiation and vegetation phenology early in the growing season

Ground-based nadir and bidirectional radiometric measurements were collected on the North Slope of Alaska in early June to determine their utility in differentiating Arctic tundra vegetation community types and examining differences in vegetation community structure and phenology. Three common Arctic vegetation types were sampled: lowland wet sedge, tussock tundra essentially devoid of woody vegetation, and tussock tundra with dwarf woody shrub vegetation. Nadir measurements alone allowed spectral differentiation between the wet sedge site and the two tussock tundra sites, but did not allow dear discrimination between the two tussock tundra sites. Bidirectional reflectance measurements, however, permitted good discrimination between the two tussock tundra sites. This outcome is largely due to the fact that normalized difference vegetation index (NDVI) values derived from measurements taken at large view zenith angles were sensitive to the woody plant foliage that extends above the hummocky tussock tundra surface early in the growing season