RETRIEVAL OF WATER-LEAVING RADIANCE AND AEROSOL OPTICAL-THICKNESS OVER THE OCEANS WITH SEAWIFS - A PRELIMINARY ALGORITHM

The second generation of ocean-color-analyzing instruments requires mo re accurate atmospheric correction than does the Coastal Zone Color Sc anner (CZCS), if one is to utilize fully their increased radiometric s ensitivity. Unlike the CZCS, the new instruments possess bands in the near infrared (NIR) that are solely for aiding atmospheric correction. We show, using aerosol models, that certain assumptions regarding the spectral behavior of the aerosol reflectance employed in the standard CZCS correction algorithm are not valid over the spectral range encom passing both the visible and the NIR. Furthermore, we show that multip le-scattering effects on the algorithm depend significantly on the aer osol model. Following these observations, we propose an algorithm that utilizes the NIR bands for atmospheric correction to the required acc uracy. Examples of the dependence of the error on the aerosol model, t he turbidity of the atmosphere, and surface roughness (waves) are prov ided. The error in the retrieved phytoplankton-pigment concentration ( the principal product of ocean-color sensors) induced by errors in the atmospheric correction are shown to be <20% in approximately 90% of t he cases examined. Finally, the aerosol thickness (tau(alpha)) is esti mated through a simple extension of the correction algorithm. Simulati ons suggest that the error in the recovered value of T(alpha) should b e less than or similar to 10%.