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Two Gated-Viewing instruments of different design, but similar mean optical power, were compared during a field test: The TRAGVIS sensor is an experimental, scientific development which was designed for particular needs of maritime search and rescue operations. The instrument uses pulsed VCSELs in the NIR, and a CMOS camera in multi-integration mode. As designed for distances < 400 m, a fixed focal length (wide angular FOV of ≈ 9° ) is used, and the repetition rate is high, while the pulse energy is low. The MODAR is a commercial multi-sensor platform comprising a Gated-Viewing instrument designed for security operations (e.g. police) both on sea and on land. Aiming at distances up to several kilometers, both camera and laser illumination are equipped with zoom optics, and the repetition rate is small, while the pulse energy is high. In contrast to TRAGVIS, an image intensifier is used. TRAGVIS and MODAR were compared in terms of signal-to-noise ratio (SNR) and image contrast using Lambertian reflectors at different distances. TRAGVIS was found to perform better than MODAR at distances < 350 m, but its performance decreases with distance while MODAR’s performance stays constant as a result of the laser and camera zoom. When used in ungated (continuous exposure) mode, TRAGVIS shows > 5 times larger SNR than in gated mode, and almost one order of magnitude larger SNR than MODAR due to the lack of an image intensifier. This demonstrates the instrument’s ability to be used for both, Gated-Viewing as well as simple active illumination mode. However, for the same reason (image intensifier) MODAR’s shutter suppression, which is crucial for reducing the back-scatter signal and therefore vision enhancement, was found to be at least 5-6 times better than that of TRAGVIS.
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