Radiometric calibration of aircraft and satellite sensors at White Sands, NM

Multiple-angle data collected in November 1988 with the Advanced Solid-State Array Spectroradiometer (ASAS), an airborne pointable imaging spectrometer covering the 450-870-nm range, have been analyzed for two sites in the gypsum sand area of White Sands, NM. Comparison of the ASAS data to surface measurements suggests that in the central portion (550-750 nm) of the spectral coverage the radiometric calibration is good (±5%), but it is less accurate at shorter or longer wavelengths. Retrieved bidirectional reflectances (BRFs) in the principal plane of the sun (53° solar zenith angle (SZA)) showed variation in both the magnitude and shape of the BRF in the alkali flat areas. The effective principal plane BRF (54° SZA) of sand dune areas departed from that of flat dune sand, particularly at forward scatter angles, due to shadowing. Current results indicate that when using White Sands as a calibration site, laboratory bidirectional measurements of gypsum sand do not adequately describe field behavior. Also, extrapolation of field bidirectional data to areas not measured may not be warranted.