RETRIEVAL OF THE COLUMNAR AEROSOL PHASE FUNCTION AND SINGLE-SCATTERING ALBEDO FROM SKY RADIANCE OVER LAND - SIMULATIONS

We present a retrieval scheme that can be used to derive the aerosol p hase function and single-scattering albedo from the sky radiance over land. The retrieval algorithm iteratively corrects the aerosol volume scattering function, the product of the single-scattering albedo and t he phase function, based on the difference between the measured sky ra diance and the radiance calculated by solving the radiative transfer e quation. It is tested first tinder ideal conditions, i.e., the approxi mations made in the retrieval algorithm totally agree with actual cond itions assumed in creating the pseudodata for sky radiance. It is then tested under more realistic conditions to assess its susceptibility t o measurement errors and effects of conditions not recognized in the r etrieval algorithm, e.g., surface horizontal inhomogeneity, departures of the surface from Lambertian, and aerosol horizontal inhomogeneity. These simulations show that, in most cases, this scheme can retrieve the aerosol single-scattering albedo with high accuracy (within 1%) an d can therefore be used to identify strongly absorbing aerosols. It ca n also produce meaningful retrievals of most aerosol phase functions: less than 5% error at 865 nm and less than 10% at 443 nm in most cases . Typically, the error in the volume scattering function is small for scattering angles less than or similar to 90 degrees, then increases f or larger angles, Disappointing results in both the single-scattering albedo and the scattering phase function occur at 443 nm, either when there are large calibration errors in the radiometer used to measure t he sky radiance or when the land reflection properties are significant ly inhomogeneous. (C) 1995 Optical Society of America.