Theoretical and experimental comparison of flash and accumulation mode in range-gated active imaging

Range-gated active imaging has significantly been improved in the recent past. Due to constraints imposed by the different types of sensors, systems using laser diodes as illumination sources are working in “accumulation” mode and systems using solid-state lasers are working in “flash” mode. Consequently, the type of source (diode or solid-state laser) gives basic differences in the behavior of the two types of systems. We systematically investigated the theoretical and practical differences between the two modes to point out their advantages and weaknesses. Parameters such as image quality, sensitivity to day light or stray light, fog penetration capacity, sensitivity to turbulence, and laser safety are examined. For comparative experimental purposes, we have built a range-gated active imaging system that allows the investigation of both illumination methods on the same sensor. We have carried out precise comparative studies between the two acquisition methods. Some differences are pointed out that have to be taken into account when designing a range-gated active imaging system in function of the desired performances. In particular, this work will help to design a new range-gated underwater active imaging system.