Removing the Ambiguity Associated with the Attenuation Coefficient Products Derived From Satellite Ocean-color Measurements

摘要

The attenuation coefficient of downwelling irradiance at 490 nm (K_d(490)) is a standard product for ocean color missions. Presently, the K_d(490) product is produced through an empirical relationship which uses the ratio of remote sensing reflectance (R_(rs)) at 489 nm and 555 nm (for SeaWiFS) as inputs. However, radiative transfer theory tells us that the attenuation coefficient of diffuse light varies with solar elevation, thus K_d(490) should also be a function of sun angle. This indicates that the current standard K_d(490) product is ambiguous, as their associated angular information is omitted. Here we present an approach that estimates such attenuation coefficients analytically, i.e. following the principle of radiative transfer. We show that the ambiguity of K_d associated with the angular information can be well corrected with such an approach.