IN-SITU MEASUREMENTS OF INELASTIC LIGHT-SCATTERING IN MONTEREY BAY USING SOLAR FRAUNHOFER LINES

The contribution of inelastic scattering processes (scattering with a change in wavelength) to the light field in the ocean can be measured directly by observing the apparent decrease in absorption (line fillin g) of the Fraunhofer absorption lines in the solar spectrum. An instru ment possessing very high spectral resolution has been developed to di rectly measure the Fraunhofer line filling in the upwelling and downwe lling irradiances as a function of depth. Measurements made in Montere y Bay show line filling similar to that predicted on theoretical groun ds when Raman scattering by water itself is assumed to be the only ine lastic process; however, the lines are filled more rapidly with depth than predicted. We believe the more rapid filling results from solar-i nduced fluorescence of dissolved organic matter. A simple model includ ing both fluorescence and Raman scattering, with the fluorescence para meters (quantum efficiency, excitation spectrum, and emission spectrum ) taken from the literature, provides a closer but not precise agreeme nt with the observations. Direct measurement bf the fluorescence param eters is likely required to achieve complete agreement with theory.