Page 294 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

10.9 Underwater optics and visibility 283
fog; the use of high-beam headlights, in most cases, causes worse viewing conditions than low- beam headlights.
Just as driving an automobile in a fog causes reduced visibility, the lighting aboard an ROV sys- tem blinds the camera through backscattering of light hitting the particulate matter suspended in the water column. In highly turbid water conditions (such as in most harbors around the world), reduction of the lighting intensity may be necessary in order to gain any level of visibility. Another consideration to aid the viewing of items underwater is the separation of the light source from the camera so that the water column before the camera is not illuminated, thus eliminating the source of backscattered lighting (Figure 10.38).
As an anecdote to lighting, Hollywood director James Cameron accomplished optimal elimina- tion of the water column’s effect during such projects as the filming of the shipwrecks Titanic and Bismarck. This was accomplished by placing the light source aboard a completely separate manned submersible (the Russian Mir-1 submersible) from the camera platform (the Russian Mir-2 sub- mersible). With small ROV platforms, the separation of lighting source from the camera point may not be possible. This may require reduced onboard lighting while taking advantage of the ambient light as back-illumination of your object of interest.
The ability to have a second vehicle like the Mir at hand is unlikely. Therefore, in very turbid water, using two or three lower-powered lights positioned efficiently on the ROV, instead of one higher-powered light, may help the situation.