Chuanmin Hu

In situ measurements of Raman scattering in clear ocean water

We have further developed and improved the prototype oceanic Fraunhofer line discriminator by using a well-protected fiber-optic-wire cable and in-water electronic housing. We conducted a series of in situ measurements in clear ocean water in the Florida Straits. By comparing the reduced data with the Monte Carlo simulation results, we verify the Raman scattering coefficient B(r) with an excitation wavelength at 488 nm to be 2.6 x 10(-4) m(-1) [Appl. Opt. 29, 71-84 (1990)], as opposed to 14.4 x 10(-4) m(-1) [Appl. Opt.14, 2116-2120 (1975)]. The wavelength dependence of the Raman scattering coefficient is found to have an insignificant effect on the in-water light field. We also discuss factors that lead to errors. This study can be used as a basis for inelastic light scattering in the radiative transfer theory and will allow other inelastic light, e.g., fluorescence, to be detected with in situ measurements.

Solar-stimulated inelastic light scattering in clear seawater

Solar Fraunhofer lines are used as indicators of the inelastic light scattering in the sea water. Data from both in-shore and off-shore are presented and compared with results of theoretical modeling. Very good agreement is found between the modeled and measured proportion of inelastic to elastically scattered and direct light at 589 nm when the Raman scattering coefficient of Marshall and Smith is used, as opposed to that of Slusher and Derr. At 656 nm the agreement is not as good, indicating possible interference from other sources such a Chlorophyll fluorescence. Recent work has extended the measurements of include smaller absorption lines, such as 689 nm, where significant filling has been measured at the surface due to the Chlorophyll fluorescence. This technique allows the natural fluorescence to be measured, even at the surface where there is still a significant amount of direct solar light.