Raman Scattering and Optical Properties of Pure Water

There are numerous observations of the spectral attenuation, absorption, and scattering of distilled water and seawater. Morel (1974) reviewed the literature with respect to the attenuation coefficient as a function of wavelength and published his seawater and distilled water scattering coefficients. Smith and Baker (1978b) critically reviewed measurements made by many investigators to estimate the relative accuracies in the published values for the total absorption coefficient and the diffuse attenuation coefficient, and found a large range. Early workers frequently did not make a careful distinction between the absorption coefficient, the diffuse attenuation coefficient, and the total beam attenuation coefficient. Preisendorfer (1976) derived a set of inequalities linking the total beam attenuation coefficient, the diffuse attenuation coefficient, the forward scattering coefficient, the average cosine, the backscattering coefficient, and the absorption coefficient. This treatment allows us to define the theoretical bounds for the inherent and apparent optical properties of optically pure water. Morel (1974) defined optically pure water as a medium devoid of dissolved and suspended material. Thus, optically pure water is a medium for which particle backscattering, particle absorption, and the absorption due to dissolved organic material are zero, so the attenuation due to the water is the absorption due to water plus molecular scattering; that is, . . . cw = aw+bm (12.1) . . . Using the relationship (Preisendorfer, 1976) one can derive an inequality for the fresh water diffuse attenuation coefficient, establishing the following limitation (in the absence of transpectral scattering): where one-half the molecular scattering is included since molecular scattering is isotropic.