The Determination of the Diffuse Attenuation Coefficient of Sea Water Using the Coastal Zone Color Scanner

Abstract

An algorithm is presented for deriving the diffuse attenuation coefficient (K) of sea water from the ratio of inherent upwelling radiances at 443 and 550 nanometers. In situ spectroradiometric data from 88 oceanographic stations taken by U.S., French and Japanese investigators working in a wide variety of water types were used to develop empirical relationships between the attenuation coefficient and the upwelling radiance (or irradiance) ratio. The relationships for estimating K’s at 490 nm and 520 nm are presented along with the error of the estimate. Errors in the determination of K from in situ measurements are also discussed.

Since the estimates of the inherent sea surface radiances can be derived from Coastal Zone Color Scanner (CZCS) data by using an appropriate atmospheric correction algorithm, a method thus exists for remotely assessing the optical properties of the surface waters of the ocean. By applying the above relationships to the inherent radiances calculated from CZCS data the attenuation coefficients for an entire CZCS scene may be rapidly obtained. An example is presented of an image representing the K (490) computed from CZCS data together with concurrent surface observations for comparison. The image shows the nature and scale of the variations of the optical properties of the coastal waters.