Under Water Laser Viewing System; ULVS
Recent technological advances have led to the realization of submersible vehicles capable of navigating at great depths, and the combination of such vehicles with high-performance cameras has come to permit televising underwater scenes featuring colorful fishes and enchanting deep-sea water-scape. In practice, however, remote viewing involves fairly severe technical difficulties when it requires viewing through turbid water; yet it is precisely such a capability that is eagerly awaited by those engaged in port and harbor works and similar domains.
In order to answer such needs in marine civil engineering, a study project on underwater viewing was started in 1992 jointly between the Ishikawajima-Harima Heavy Industries Co., Ltd.(IHI), the 1st District Port Construction Bureau and the Port and Harbor Research Institute of the Ministry of Transport.
New developments of recent years related to the range gate camera have led to the realization of an ultra-short-pulse high output illuminating system that can produce a pulsating light of intensity exceeding 100mJ repeated at a rate of around 50Hz and with a duration of several nanoseconds.
Experiments have been performed to seek the dependence of laser ray attenuation in water on wavelength, on water turbidity and on suspended particle size. Results of trial runs have proved appreciable improvement of image quality to be obtainable with the laser viewing system. Simulation has been applied to fill the gaps between discrete points determined by experiment to obtain optimum values for the parameters governing the viewing system.
We have successfully undergone actual site work experiment with the use of our prototype at Niigata minato tunnel caisson setting on the 21st July, 1996.
Fig. 1 shows IHI made prototype laser generator and cooler on the left, control panel with monitor at midst and viewing unit on the right.
Fig. 2 shows comparison of images of aluminun cans and bottle between ULVS and conventional SIT camera.
New design of handy type ULVS has been developed and will be on the market in the near future.
