Measured and modelled optical properties of particulate matter in the southern Benguela

• Published in: South African journal of science Vol. 97; no. 9-10; pp. 410 - 420
• Main Authors: Bernard, S, Probyn, T A, Barlow, R G
• Format: Journal Article
• Language: English
• Published: 01.10.2001
• Subjects: PSW, South Atlantic, Benguela Upwelling
• ISSN: 0038-2353

Particulate absorption, particle size distributions and HPLC-derived pigments were used in combination with particle scattering models to examine the optical properties of natural algal assemblages in the southern Benguela. Inverse anomalous diffraction (IAD) models were used to derive the real and imaginary parts of the mean spherical equivalent particulate refractive index from absorption and particle size measurements. Such data were utilized with an homogeneous sphere Mie model to calculate particulate backscattering coefficients. The influence of natural particle size distributions on the ability of the IAD model to return unique refractive index values was assessed. Measured absorption and modelled backscattering coefficients, in addition to derived optical efficiency factors, were examined with regard to the influence of size, refractive index parameters and the variability of algal assemblages in the southern Benguela. The real part of the refractive index, as determined by the IAD model, was demonstrated to be a useful descriptor of algal assemblage structure. Significant non-linear relationships were established between the algal backscattering: absorption ratio and the real part of the particulate refractive index, indicating the potential to calculate the real part of the particulate refractive index from ocean colour data.