Effect of Raman scattering on the average cosine and diffuse attenuation coefficient of irradiance in the ocean

Abstract

We have investigated the effect of Raman scattering on the average cosine of underwater irradiance, ,%, the diffuse attenuation coefficient of irradiance, K, and the Raman scattering source coefficient, P*, throughout the water column and into the asymptotic field. The Raman scattering source coefficient is the fractional gain in the scalar irradiance from local Raman scattering at a given depth, and it can be found from the Gershun equation with a Raman source term. In particular, by using calculations from a radiative transfer model (Hydrolight 3.0), we compare ,%, K, and P* from simulations that include and that omit Raman scattering. These simulations are performed at wavelengths between 355 and 665 nm in a vertically homogeneous ocean 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-j). 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 present, there may exist strong vertical gradients in the average cosine and the diffuse attenuation coefficient, especially at long wavelengths 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, there is no effect of Raman scattering at shorter wavelengths, there is a strong effect of Raman scattering at longer wavelengths and between these two spectral regions, and there is a transition that increases from 500 to 590 nm as the concentration of chlorophyll increases from 0.05 to 5 mg m-2. Over a broad range of IOPs, the asymptotic parameters pm*, K,*, and P*, are related by a quadratic relationship. Neither the magnitude or angular distribution of surface light nor changes in the absorption and scattering coefficients in the surface layer of a two-layered ocean have auy effect on the values of ,%=*, K,*, and P*,; the values of these parameters depend only upon the IOPs in the deepest layer.

In situ determination of the quantum yield of phytoplankton chlorophyll a fluorescence: A simple algorithm, observations, and a model

“…Both in situ and cultured fluorescence emissions have been characterized using a Gaussian peak centered around 683 nm with a 10.6-nm standard deviation (Gordon 1979;Prézelin and Ley 1980;Kishino et al 1984;Collins et al 1985), and the emission appears to be spectrally independent of the excitation wavelength (Myers and Graham 1963). Raman scattering by water, with excitation wavelengths around 555 nm, is another potential inelastic source (Berwald et al 1998;Maritorena et al 2000). The high absorption of water at red wavelengths compared with those in the blue and green regions of the spectrum leads to increasing dominance of inelastically scattered light at chlorophyll fluorescence wavelengths with increasing depth (Kishino et al 1984;Kiefer et al 1989).…”

Genesis and evolution of polarization of light in the ocean [Invited]

“…Due to the lack of high intensity light sources and accurate spectrometers, it took nearly 50 years before the evidence of the Raman effect in water was established. The Raman scattering effect on the diffuse attenuation coefficient and other optical properties, were noted by Morel [50], Bristow et al [51], Hoge and Swift [52,53], Sugihara et al [45], Stavn and Weidemann [54], Marshall and Smith [55], Kattawar and Xu [56], Berwald et al [57], and others. And only Gordon et al [58] and Gordon and Xu [59] have analyzed the asymptotic field with Raman scattering.…”

Copper Multilayer Interconnection Using Ultravaiolet Nanoimprint Lithography with a Double-Deck Mold and Electroplating

“…In figure 4(a), the fluorescence signal increases with increasing Chl-a concentrations (0.9-2.9 mg m −3 ) and a notable increase towards the shorter wavelength side (particularly within 650-660 nm) may result from inelastic scattering (photons undergo changes in frequency and polarization). The contribution of inelastically scattered radiation is normally high at low Chla concentrations [38,39], but significantly diminishes with increasing Chl-a concentrations. This is particularly evident in figures 4(b)-(e), where the fluorescence signal becomes increasingly detached from such contributions.…”