Concept Design Phase Expendable Holographic Sensor to Measure Ocean Small Angle Optical Scattering.

摘要

A preliminary design concept has been developed for a holographic instrument to measure scattering and beam transmission optical properties of ocean waters. The expandable instrument is being developed for use with ship or aircraft deployment using the XDT/AXBT technology. The instrument design has been separated into four measurement functions: (1) beam transmission, (2) small angle scattering, (3) large angle scattering, and (4) backscatter. The present research has focussed on developing and demonstrating a holographic design to measure small angle scattering. This instrument measures the modulation transfer function (MTF) of the particles suspended in the water. The MTF can be inverted with a Fourier-Bessel transform procedure to estimate the volume scattering function at small angles. A laboratory demonstration hologram was constructed to focus a sinusoidal pattern scattered by polystyrene spheres onto a linear detector array. The laboratory results showed loss of contrast with increasing spatial frequency. Simulation model results for a 25cm instrument demonstrated the capability to measure contrast loss at selected spatial frequencies and used that information to derive the volume scattering function for angles from 0.005 deg to 0.5 deg. (Author)