The Effects of Particle Size on Contrast Improvement by Polarization Discrimination for Underwater Targets

Luminous flux was measured from an underwater target illuminated by circularly polarized lamp. Backscatter was measured with and without a circular analyzer on the telephotometer. Turbidity of the water was controlled by adding polystyrene spheres of relative refractive index m = 1.20. Contrasts were determined as a function of particle diameter and concentration for spheres ranging from 0.126 micro to 1.099 micro and for three size distributions from 6 micro to 100 micro. A ratio comparison of the contrasts showed a definite improvement for scatterers of diameters > 1 micro. Contrast degraded for CP illuminated scattering from spheres in the 1-100-micro diam range. Considering the ocean's scatterer-size distributions, circular polarization will probably most improve contrast in the vertical region from the lower euphotic zone to a few meters above bottom.