ATMOSPHERIC CORRECTION OF OCEAN COLOR IMAGERY - USE OF THE JUNGE POWER-LAW AEROSOL-SIZE DISTRIBUTION WITH VARIABLE REFRACTIVE-INDEX TO HANDLE AEROSOL ABSORPTION

When strongly absorbing aerosols are present in the atmosphere, the us ual two-step procedure of processing ocean color data-(1) atmospheric correction to provide the water-leaving reflectance (rho(w)), followed by (2) relating rho(w) to the water constituents-fails and simultaneo us estimation of the ocean and aerosol optical properties is necessary . We explore the efficacy of using a simple model of the aerosol-a Jun ge power-law size distribution consisting of homogeneous spheres with arbitrary refractive index-in a nonlinear optimization procedure for e stimating the relevant oceanic and atmospheric parameters for case 1 w aters. Using simulated test data generated from more realistic aerosol size distributions (sums of log-normally distributed components with different compositions), we show that the ocean's pigment concentratio n (C) can be retrieved with good accuracy in the presence of weakly or strongly absorbing aerosols. However, because of significant differen ces in the scattering phase functions for the test and power-law distr ibutions, large error is possible in the estimate of the aerosol optic al thickness. The positive result for C suggests that the detailed sha pe of the aerosol-scattering phase function is not relevant to the atm ospheric correction of ocean color sensors. The relevant parameters ar e the aerosol single-scattering albedo and the spectral variation of t he aerosol optical depth. We argue that the assumption of aerosol sphe ricity should not restrict the validity of the algorithm and suggest a n avenue for including colored aerosols, e.g., wind-blown dust, in the procedure. A significant advantage of the new approach is that realis tic multicomponent aerosol models are not required for the retrieval o f C. (C) 1998 Optical Society of America.