Ranges obtainable in underwater viewing are severely limited by backscattering. Increased ranges are possible by means of the range-gating technique, which gates out most of the unwanted backscattering electronically. Tests were conducted in filtered fresh water to determine the performance of a range-gating system and the characteristics of water in terms of image quality or resolution. A pulsed blue-green laser source and a highly sensitive receiver were used. Results indicate that range-gated systems are effective for underwater viewing up to 131 feet with good resolution. Comparison tests in a laser-illuminated ungated mode, a back-illuminated mode, and a front-illuminated mode were conducted concurrently.
"Recent Underwater Range-Gated Measurements", Proc. SPIE 0012, Underwater Photo-Optical Instrumentation Applications II, (1 August 1968); doi: 10.1117/12.946728; https://doi.org/10.1117/12.946728