Feasibility testing of a range-gated laser-illuminated underwater imaging system

Abstract

Range-gated underwater imaging has long been a popular topic for discussion and analysis; however, current laboratory data from such a system in operation is not readily available. In the summer of 1989, the authors configured a range-gated, laser-illuminatedimaging system utilizing "off-the-shelf" equipmenttodemonstrate the feasibility ofusing this technique. Using an intensified, gated, solid state video camera, a pulsed-frequency doubled Nd:YAG laser, a time delay generator, and an optical delay to compensate for system delays, a range-gated testhed was configured with the capability to record image slices through the water volume movable in 1 ns increments. A time delay generator and an optical delay to compensate for fixed system delays were configured to gate the camera to take image slices through the water, moving in 1 ns steps. The tests consisted of placing the target at various depths to 40 feet as the turbidity of the water was varied and measured. The images were collected on video tape and later digitized and analyzed. Details of the experimental configuration and test results are presented.