Improvement of underwater viewing range by the use of a scanning laser-based illuminator

Describes the achievement of range-gated systems and volume scanning systems but points out that, as yet, the various markets for underwater vision systems have not been supportive of such relatively high cost solutions. The authors describe the Cranfield Scanning Illuminator in which the image is captured by the use of a standard underwater television camera possessing a standard field of view and using no scanning optics. The light source is an Amoco type ALC 532-5 CW frequency-doubled, diode-pumped Nd:YAG laser operating at 532 nm, a wavelength which experiences relatively low attenuation in most seawater types. Scanning of the beam is achieved by the use of two galvanometer mounted mirrors. The underwater camera used in conjunction with the illuminator is a standard silicon intensified target monochrome Osprey type 1321 camera. The principles of operation and parameters affecting the performance are outlined