Determination of the Shortwave Anisotropic Function for Clear-Sky Desert Scenes from ScaRaB Data: Comparison with Models Issued from Other Satellite Data

Abstract

Determination of directional albedo and bidirectional anisotropic function are necessary to the radiance-to-flux conversion. The most recent model, used for the Earth Radiation Budget Experiment data, is based on data from the sun-synchronous Nimbus-7 mission that is observed close to local noon. Because the desert zones are restricted in latitude (20°?35° in each hemisphere), only a small range of solar zenith angles was sampled. Here, the author considers for clear-sky desert regions the improvements that can be made using non-sun-synchronous satellite data, precessing in local time. This study made from ScaRaB data (Scanner for Radiation Budget, on board the Meteor-3-07 satellite) concerns the clear-sky deserts. The four great deserts on the earth (the Sahara, Arabian Desert, Namib-Kalahari, and Australian Desert) have been considered with 1.25° latitude ? 1.25° longitude study areas. A normalization method, explained here, makes it possible to combine the values of bidirectionel anisotropic reflectances of all of these areas. Only one characteristic function is obtained for each desert. It is shown how the characteristic function of the Sahara may be extended to the bright deserts (the Sahara and the Arabian Desert) and how the characteristic function of the Australian Desert may be extended to the dark deserts (the Australian Desert and the Namib-Kalahari). This study concludes with a comparison of the albedo and anisotropic functions obtained from different models.