Feasibility study on LED-based underwater gated-viewing for inspection tasks

A nanoseconds-pulsed LED illuminator design for underwater vision enhancement by gated-viewing is investigated and discussed in comparison to a state of the art laser source. An initial experiment in a turbid harbour at 2.5 to 3.0 attenuation lengths shows an increase in image contrast by a factor of about 2 to 6 achieved by an LED gated-viewing in comparison to non-gated, active and passive camera systems. In addition, an analysis of beam attenuation spectra in coastal areas of potential operation has been conducted. Different LEDs have been characterised, using a 6 ns electrical trigger pulse width. With this setup, optical pulse energies up to 7.2 nJ per LED at optical pulse widths of 4.6 ns could be achieved. The photon return of an upscaled LED-based illuminator in a coastal environment is estimated and its characteristics, potentials and drawbacks are discussed.