An AUV-deployable pulsed laser line scan (PLLS) imaging sensor

Abstract

Laser line scan (LLS) underwater imaging is a serial imaging technique that involves the optical scanning of a narrow instantaneous field of view (IFOV) receiver in a synchronous fashion with a highly collimated laser source over a wide swath. It is widely regarded as the optimal technology for extended range underwater optical imaging, with up to 6 attenuation lengths achievable in turbid seawater. These imagers, which utilize high power green CW lasers, require an adequate source- receiver separation to reduce near field backscattering image degradation. They have been successfully deployed onboard towed bodies, and have potential as AUV-deployed imagers except their large size and high sensitivity to changes in operating conditions and environment makes them difficult to use successfully with these platforms. Harnessing recent developments in high power, high repetition rate green pulsed lasers, high speed gate-able photomultiplier tubes, rapid parallel digital signal processors and compact underwater scanning systems, this paper describes the latest approach to demonstrating a prototype pulsed laser line scan (PLLS) imager which has the required compactness and ease of operability to make it more compatible for implementation onboard the common classes of AUV.