THE VARIATION IN THE INHERENT OPTICAL-PROPERTIES OF PHYTOPLANKTON NEAR AN ABSORPTION PEAK AS DETERMINED BY VARIOUS MODELS OF CELL STRUCTURE

Optical oceanography models of attenuation and scattering properties o ften contain simple spectral relationships. Electromagnetic theory, ho wever, predicts fluctuations in the spectra of the attenuation coeffic ients and scattering properties of substances at wavelengths near an a bsorption peak. We have modeled these effects for phytoplankton using homogeneous, two-layered, and three-layered sphere models of cell stru cture and using a wide range of plausible particle size distributions. The magnitude of the scattering in backward directions is affected th e most. The effect on the beam attenuation spectra is relatively small compared with the effect on the absorption and scattering coefficient s. The backscattering coefficient shows large variability, varying by almost a factor of 3 for some models. The results suggest that beam at tenuation at any wavelength in the red shorter than the wavelength of the chlorophyll absorption peak will be insensitive to the chlorophyll content of the particles. Increases in the pigment content per unit v olume of phytoplankton will increase the index of refraction in the in frared and therefore increase the attenuation and scattering coefficie nts there.