Underwater optical ranging system for ROVs

Presents a technique for an underwater vision system based on the time of flight technique. The system produces 3D images consisting of 2D intensity images and range images. The system consists of a modulated laser as the source, an image dissector tube camera with pixel resolution, a phase measuring unit and a host PC with associated interface boards. Two laser sources provide a red laser beam (670 nm wavelength with 10 mW(max.)) and a green laser (532 nm wavelength with 300 mW(max.)). An amplitude modulation frequency in the MHz region has been used. The range information was obtained by measuring the phase difference between the transmitted and the received signal. Tests were conducted with the salt concentration adjusted to match the salt concentration of various types of water. Results of the vision system in these conditions are shown. The underwater vision system was successfully used to obtain the range images of a few basic shapes in the laboratory water tank environment. From the experimental results, it is concluded that this technique is suitable for an underwater vision system and other applications.