Deriving reciprocal kernel functional expression of Antarctic sea ice surface BRDF from field measurements

We investigate derivation of kernel functional expression of Antarctic sea ice surface BRDF using field measurements. Two new methods we developed recently are used to expand the scope and enhance the use of field albedo and reflectance measurements. The first normalizes, among ice stations of the same ice type, the BRDF difference caused by slight differences in the physical properties of the ice cover. The second method derives direct beam spectral albedo from hemispherical directional spectral reflectance measured under overcast skies using the reciprocity between them. The derived direct beam spectral albedo estimates cover the full range of solar zenith angles. We combine the resulting data sets together to determine the coefficients of the BRDF kernel functions through stepwise linear regression. The derived BRDF kernel functional expression is representative of the ice type of interest, and is optimized in the sense that the ordinary limitation of narrow solar zenith angle range no longer exists. The resulting BRDF expression will contribute to improving derivation of sea ice surface albedo from remote sensing measurements.