Underwater Laser Imaging System Research Articles

Underwater Target characterization and laser imaging system

Underwater Target characterization and laser imaging system

距离选通水下激光成像系统设计及实验

距离选通水下激光成像系统设计及实验

Underwater image restoration by means of blind deconvolution approach

Although the use of blind deconvolution of image restoration is a widely known concept, little literatures have discussed in detail its application in the problem of restoration of underwater range-gated laser images. With the knowledge of the point spread function (PSF) and modulation transfer function (MTF) of water, underwater images can be better restored or enhanced. We first review image degradation process and Wells’ small angle approximation theory, and then provide an image enhancement method for our underwater laser imaging system by blind deconvolution method based on small angle approximation. We also introduce a modified normalized mean square error (NMSE) method to validate the convergence of the blind deconvolution algorithm which is applied in our approach. The results of different initial guess of blind deconvolution are compared and discussed. Moreover, restoration results are obtained and discussed by intentionally changing the MTF parameters and using non-model-based PSF as the initial guess.

A novel application of range-gated underwater laser imaging system (ULIS) in near-target turbid medium

Range-gated imaging system improves signal-to-backscattering noise ratio (SBR) by rejecting backscattered light from the target irradiance. This is achieved by synchronizing the arrival of pulsed target irradiance with the gating of an intensified camera. Witherspoon and Holloway (Ocean Optics X 1302 (1990) 414–420) indicated that the image quality of range-gated imaging system might be further improved by a delay in the camera gating towards the tail of reflected image temporal profile (RITP). This phenomena has, however, not been further elaborated. This paper extends on Witherspoon's observation. The MCRITP (Monte Carlo for RITP) algorithm is validated with theoretical and experimental results for medium attenuation coefficients of 0.26–5.90/m. By temporal convolution of the simulated results with outgoing Gaussian light pulse, Tail RITP region shows more reduction in the unwanted backscatter effects than the target intensity. This can be observed as an improvement in image contrast and a modified fidelity index (MF).

Range-gated underwater laser imaging system

A careful analysis of a scattering and absorption database of the waters off the coasts of Canada shows that a laser-assisted camera system will have a significantly improved viewing performance over conventional systems. The laser underwater camera image enhancer system is a range-gated laser system that can be mounted on a remotely operated vehicle. The system uses a 2-kHz diode-pumped frequency-doubled Nd:YAG laser as an illumination source. The light is collected by a 10-cm-diam zoom lens. The detector is a gated image intensifier with a 7-ns gate and a gain that is continuously variable from 500 to 1,000,000. The system has been tested in a water tank facility at Defence Research Establishment Valcartier and has been mounted on the HYSUB 5000 remotely operated vehicle for sea trials. In the strongly scattering waters typical of harbor approaches, this system has a range of from three to five times that of a conventional camera with floodlights.