Variability of the bare soil albedo due to different solar zenith angles and atmospheric haziness

Abstract

Owing to the non-Lambertian reflection properties of natural surfaces, the bidirectional reflectance factor (BRF) and hence the albedo depend on solar zenith angle (SZ) as well as the haziness of the atmosphere. By using the results of Pinty, Verstraetc and Dickinson to describe the BRFs of bare soil in NOAA-7, -8 satellite AVHRR band 1 and 2, and the results of LOWTRAN-7 as the description of hemispherical irradiation, the variation of bare soil albedo and errors inferred from all viewing directions of BRF under changing SZs and aerosol optical depths is discussed. This paper also shows that the optimal view angle of bare soil used to infer the albedo from a single observation under SZ from 25° to 45°, and atmospheric conditions from clear sky to hazy sky, for both AVHRR bands is about 50° off-nadir and about 80° relative azimuthal angle. Their errors are no more than 1 per cent. The sensitivity of optimal view angle with aerosol optical depth is also discussed. This leads to the evaluation of the optimal view angle determined by Kimes and Sellers at different haziness of atmosphere.