Effect of a Polydisperse Hydrosol on the Spectral Properties of Light Scattering by Seawater at Forfard Angles

Abstract

In this paper we discuss the problem how to analyze the results of spectral volume scattering function measurements in natural waters and artificial ones. Analytical predictions and experimental proves of the remarkable changes in the properties of the light scattering at small angles after a filtration of water sample are presented. It was proposed that a certain correlations in the positions of scattering centers always exist in the water which were resulted in the volume scattering function of any natural water was strong forward peaked. Based on Mie theory the sums of scattering amplitudes and scattering radiances were calculated for a power-law particle size distribution while the maximal radius was varied. The square of the sum of the scattering amplitudes was compared with the value of the classical term. It is shown that in the “blue” a significant compensation of the effect of spatial correlation of particles occurs with an increasing of the maximum radius of particles, starting from the radius is about 0.2 μm. The contribution of the additional term decreases faster at general angles region. The spectral properties of light scattering by seawater during sequential filtration through nucleopore filters with a pore diameter of 2, 1, and 0.45 μm have been measured. The volume scattering function data at scattering angles from 6 to 90 degrees were analyzed. Water samples were taken from the surface of the Black Sea at the beginning of October. The Secchi depths are varied from 16 up to 19m. It was found that after filtration through a filter with pores diameter equaled to 1 μm, the typical deep at 30° of spectral slope of volume scattering function was appeared. Such deep becomes stronger after the next stage of filtration, when diameter of pores was equal to 0.45 µm. It is shown that the angular dependence of the exponent of the spectral slope obtained as a result of processing the experimental data is in consistent with theoretical predictions.