Underwater imaging by laser: polarization labelling

Abstract

In underwater optical imaging by laser the authors have tested the efficiency of polarization labelling for discrimination and identification of immersed targets. Range-gating techniques have been used; the light source was a pulsed Nd-YAG laser emitting at lambda =532 nm and the imaging detectors either a gated digital camera (for global imaging) or a photomultiplier associated with a transient analyser (for scanning imaging). These systems are able to eliminate the signal backscattered by the medium and so to separate the polarization transformation produced by the target from that of the scattering particles of sea-water. For a scanning imaging system, Mueller matrix coefficients can be calculated to get a depolarization criterion for different materials: associated with intensities values this parameter can, for example, contribute to classify different targets in bidimensional diagrams.