In order to support maritime search and rescue activities, an affordable gated-viewing instrument has been developed within the TRAGVIS project. The instrument, which got the name TRAGVIS after the project’s name, has the purpose of vision enhancement during night-time missions under bad visibility conditions. TRAGVIS consists of a compact, eye-safe NIR (near-infrared) laser light source and a monochromatic 1.3 Mpixel camera and has a field of view similar to the one of common field glasses. The camera sensor was recently upgraded from the Onyx to the Bora rev.A sensor from Teledyne–e2v, and a thorough comparison will be shown between them. Several field tests were conducted on an out of service airport and in a maritime environment. The measured gray values of the instrument were calibrated to the reflectivity of the targets at different distances. Furthermore, the performance of the instrument has been studied under different visibility conditions. Therefore, several images of the same target were taken with the gated-viewing mode enabled and disabled. These measurements showed that even during the presence of a light fog with an extinction coefficient of 3.8 km−1, the measured contrast decreased by more than a factor of 3 when gated-viewing was disabled. Contrary to this, no significant decrease in the contrast could be identified using the gated-viewing feature of our instrument. In the maritime environment, field tests at a close harbor were performed for the identification of different maritime objects such as sailing boats, rubber boats and drones. Using several TRAGVIS images taken at monotone increasing gate distances, a simple method was applied to build three dimensional images of this maritime scenery.
A novel gated-viewing instrument is presented for vision enhancement in maritime search and rescue applications predominantly under limited visibility conditions at night. The compact device consists of a camera and an eye-safe NIR (near-infrared) illuminator and has a field of view of ≈7° x 6°, which is similar to field glasses. The detection range is 250 m for Lambertian reflectors, but is much larger if clothes with retro-reflectors are worn. A key challenge is the cost effectiveness of the instrument as potential users in the field of maritime search and rescue applications usually suffer from financial limitations. As a result, no image intensifier, but an off-the-shelf CMOS camera in accumulation mode with a reasonable quantum efficiency in the NIR region is used. The active illumination is based on a self-developed illuminator consisting of 7 pulsed vertical-cavity surface-emitting laser (VCSEL) arrays. The mean optical power is 7 W, the center wavelength is λ≈804 nm, and the light pulse width is ≈100 ns at a repetition rate of 345 kHz. Detailed simulations leading to the system design are presented together with respective characterization measurements of the camera and illuminator as well as first test measurements of the complete system.