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 μ to 1.099 μ and for three size distributions from 6 μ to 100 μ. A ratio comparison of the contrasts showed a definite improvement for scatterers of diameters < 1 μ. Contrast degraded for CP illuminated scattering from spheres in the 1–100-μ 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.
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