Electronic improvement of underwater scene rendition: A discussion of range controlled AGC for active underwater optical viewing systems

The intent of this paper is to suggest areas where beneficial changes might be made in the display of underwater scenes. Presently, the turbidity of the water medium produces a rapid scene-brightness fall -off that carries over into the system´s display. In addition to this problem, the second-generation viewing systems (range gate and synchronous scan) possess spatial peculiarities that appear as voids in their displays. Voids or rapid graying-out of the scene or both can be moderated by certain system gain-control techniques. In addition to presenting approaches to range-controlled gain, this paper restates the criteria, or conditions that can reasonably be expected in the display. The major effort, however, is directed to modifications applicable to the range-gate and synchronous-scan systems because the greatest departures from the display criteria are found in these systems.