Holographic instrument to measure small-angle scattering
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A design concept has been developed for a holographic instrument to measure scattering and beam transmission properties of ocean waters. The holographic concept not only uniquely supports the measurement technique but allows for a possible compact expendable design. This holographic design measures the medium modulation transfer function (MTF) at specific spatial frequencies and uses these data to approximate the complete MTF with a spline blending technique. A sinusoidal bar pattern is imaged by diffraction optics as a two dimensional pattern through the water medium and tank faces onto a linear detector array and recorded as contrast loss. A Fourier-Bessel transform technique was used to retrieve the small angle scattering function in the angular region from 0.005 degree(s) to 0.5 degree(s). Monte Carlo simulations of the instrument with sample path lengths of 25 and 100 cm and Tongue of the Ocean water types are used to demonstrate performance. The instrument design hologram was constructed for an initial set of laboratory particle seeding experiments. Results were found to be consistent with those generated from model simulations using Mie calculated scattering functions for sample particle size distributions.
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