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16 July 2007 Polarimetry as tool to improve phase measurement in an amplitude modulated laser for submarine archaeological sites inspection
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The propagation of polarized laser beams in turbid water is a subject of relevant interest in the field of underwater quantitative visualization with active sensors like amplitude modulated laser systems. In such devices, target range determination is based on the measurement of the phase difference ΔΦ between the fraction of the amplitude modulated laser beam reflected by the target and a reference signal. As water turbidity increases, the laser radiation backscattered from the water column shined by the sounding laser beam gives rise to an optical background with detrimental effects on the accuracy of range measurement. In this paper we analyze the possibility to increase the apparatus accuracy with a polarimetric technique based on the adoption of polarized laser radiation and polarization selective detection scheme for improving the underwater imaging of real scenes (e.g. archaeological sites). The method fully takes advantages of the different polarization properties of the laser radiation backscattered by turbid water and of the Lambertian component diffusively reflected by the target as described by the associated Mueller matrices. Measurements have been performed by adopting both a co-polarized and cross-polarized detection scheme with linearly and circularly polarized laser radiation. Various degrees of turbidity were realized by adding, as diffusive element, skim milk to water in order to obtain different scattering conditions. The effect of the transition from Rayleigh to Mie scattering regime on phase accuracy determination has been investigated together with the role played by high order scatterings as the medium approaches the optical thickness condition.
© (2007) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
L. Bartolini, L. De Dominicis, M. Ferri de Collibus, G. Fornetti, M. Francucci, M. Guarneri, E. Paglia, C. Poggi, and R. Ricci "Polarimetry as tool to improve phase measurement in an amplitude modulated laser for submarine archaeological sites inspection", Proc. SPIE 6618, O3A: Optics for Arts, Architecture, and Archaeology, 66180I (16 July 2007);

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