Imaging Systems for Advanced Underwater Vehicles

Exploration of the underwater environment either by human operated or by autonomous vehicles can highly benefit from using a visual imaging system. When a vision system for an underwater vehicle has to be designed, some specific characteristics of the image formation in sub-sea conditions should be taken into account. This paper presents an extensive survey of components, techniques and methods used to build underwater vision systems. First, most of the phenomena that affect the image formation in submersed conditions are described; second, some significant illumination techniques and light sources, including laser, are presented; and third, the review follows with a list of relevant underwater visual installations and submarine vehicles with vision-based infrastructures recently developed and commercially available. Furthermore, the paper finally introduces some techniques for improving the quality of underwater images. Among all these techniques, a special attention has been paid to the effect of employing polarized light to overcome the undesired scatter present in images. This last section includes some experiments carried out by the authors to test the usefulness of polarization-based methods in robotic applications.