EFFECT OF RAMAN-SCATTERING ON THE AVERAGE COSINE AND DIFFUSE ATTENUATION COEFFICIENT OF IRRADIANCE IN THE OCEAN

We have investigated the effect of Raman scattering on the average cos ine of underwater irradiance, <(mu)over bar>, the diffuse attenuation coefficient of irradiance, K, and the Raman scattering source coeffici ent, P, throughout the water column and into the asymptotic field. Th e Raman scattering source coefficient is the fractional gain in the sc aler irradiance from local Raman scattering at a given depth, and it c an be found from the Gershun equation with a Raman source term. In par ticular, by using calculations from a radiative transfer model (Hydrol ight 3.0), we compare <(mu)over bar>, K, and P from simulations that include and that omit Raman scattering. These simulations are performe d at wavelengths between 355 and 665 nm in a vertically homogeneous oc ean with inherent optical properties (IOPs) determined from case 1 bio -optical models for three different chlorophyll concentrations (0.05, 0.5, and 5 mg m(-3)). We also investigated several two-layered oceans that assumed different inherent optical properties in the surface and deep layers. Our calculations showed that when Raman scattering is pre sent, there may exist strong vertical gradients in the average cosine and the diffuse attenuation coefficient, especially at long wavelength s for low chlorophyll concentrations. In addition, a quasi-asymptotic field may be a feature of the vertical profiles of the average cosine and the diffuse attenuation coefficient. In the asymptotic field, ther e is no effect of Raman scattering at shorter wavelengths, there is a strong effect of Raman scattering at longer wavelengths and between th ese two spectral regions, and there is a transition that increases fro m 500 to 590 nm as the concentration of chlorophyll increases from 0.0 5 to 5 mg m(-3). Over a broad range of IOPs, the asymptotic parameters <(mu)over bar>(infinity), K-infinity*, and P*(infinity) are related by a quadratic relationship. Neither the magnitude or angular distribu tion of surface light nor changes in the absorption and scattering coe fficients in the surface layer of a two-layered ocean have any effect on the values of <(mu)over bar>(infinity), K-infinity*, and P*(infini ty),; the values of these parameters depend only upon the IOPs in the deepest layer.