Airborne spectral measurements of surface-atmosphere anisotropy for arctic sea ice and tundra

Angular distributions of spectral reflectance for four common arctic surfaces: snow-covered sea ice, melt-season sea ice, snow-covered tundra, and tundra shortly after snowmelt were measured using an aircraft-based, high angular resolution (1degrees) multispectral radiometer. Results indicate bidirectional reflectance is higher for snow-covered sea ice than melt-season sea ice at all wavelengths between 0.47 and 2.3 mum, with the difference increasing with wavelength. Bidirectional reflectance of snow-covered tundra is higher than for snow-free tundra for measurements less than 1.64 mum, with the difference decreasing with wavelength. Bidirectional reflectance patterns of all measured surfaces show significant reflectance maxima in the forward scattering direction of the principal plane with identifiable specular reflection for the melt-season sea ice and snow-free tundra cases. The snow-free tundra had the most significant backscatter (similar to other vegetative bidirectional reflectance patterns such as for Cerrado in Brazil), and the melt-season sea ice the least. For sea ice, bidirectional reflectance changes due to snowmelt were more significant than differences among the different types of melt-season sea ice. The spectral-hemispherical ( plane) albedo of each measured arctic surface was also computed. Comparing measured nadir reflectance to albedo for sea ice and snow-covered tundra shows nadir reflectance 5-40% smaller, with the largest difference at wavelengths beyond 1 mum. For snow-free tundra, nadir reflectance is 30-50% smaller than the plane albedo.