<title>Laser gated-ranging for underwater robot vision in turbid waters</title>

Abstract

Although developments of Remotely Operated Vehicles have been rapid, the underwater robot vision is still regarded as a major tough undertaking when being maneuvered by a remote pilot, particularly in turbid water condition. Sonar imaging offers a large range for detection but often falls short in achieving the required resolution for identification. Normal optical image method such as underwater camera offers inherently high resolution capability, but the absorption and scattering characteristic of marine medium severely limits range performance, e.g. the visible range in Singapore coastline area is 2-3 meter. Currently, an experimental underwater laser gated-ranging system for underwater robot vision has been finished and precisely demonstrated ns-level gated images in highly turbid waters. We are first to study in such a 3-m short water tank with highly turbid waters successfully, and show the range-gated phenomenon much more clearly based on our newly-designed series targets. The target-set is a series of three bar test targets at intervals of 22.5 cm since the light speed in water is 22.5 cm/ns. We synchronize to range-gate on the targets which we want to have its image, and to gate out the targets which we don't want its image. The attenuation coefficient in the turbid water tank is 1.0/m and 2.3/m separately.