With optical viewing systems the protection status of maritime infrastructures (e.g. harbors, container terminals and offshore windfarms), as well as the safety for people working at sea can be improved. Accidents at sea can happen every time, everywhere and under bad weather conditions. Resulting search and rescue (SAR) can take couple of hours, partly up to several days.
For an effective search and rescue at night the human eye and passive instruments are insufficient. Furthermore, the visibility conditions can be decreased – for example heavy rain or dense banks of fog – that classical visual exploration systems remain ineffective. In such cases active sensor systems with an integrated light source are an approach with high potential.
Figure 1: Measurement principle Range-gating
The project TRAGVIS (Transportable RAnge-Gated Viewing System) is dedicated to develop a gated-viewing system for the need of maritime search and rescue. Range-gating systems consist of a camera system, which is coordinated with an active pulsed (laser-)light. The illuminating pluses of the light source are synchronized with the shutter of the camera. This technique suppresses atmospheric backscattering by particles und water droplets. In addition, different depth levels can be resolved in the image.
Figure 2: TRAGVIS (foreground) and thermal and normal camera at the North Sea
Available range-gating systems are often too large and heavy. For effective use on small search and rescue boats, the sensor has to be light and small. The goal of project TRAGVIS is to develop a small, cost-effective and light sensor, which is satisfactory for the end-user. For this purpose, and following tests at sea, a cooperation agreement was concluded with the German Maritime Search and Rescue Service (Deutsche Gesellschaft zur Rettung Schiffbrüchiger; DGzRS).
In the first phase of the project existing detector and light source technologies are identified. In a parallel process a requirement analysis has been made.
In the second phase the developed sensor system was installed on the roof of the institute. In this way long term data of different visibilities can be collected and compared to simulated data.
In the third phase the optimized sensor unit was tested on a search and rescue vessel of the DGzRS. The focus on these tests was to detect persons and specific floating objects in water.
Figure 3: Image thermal camera
The results of the test are evaluated at the moment and are exemplarily outlined for one scene. The scene is recorded with different camera systems. The left image shows the scene recorded with the developed range-gated system, the daughter boat and dummy can be recognized. The dummy has no retroreflectors, because in real SAR it is not expected, that missing persons wear clothes with reflectors. It is mandatory, that the system can recognize vague reflecting objects floating in the water. Furthermore, the daughter boat can be seen clearly. In the middle the same scene is shown with a thermal camera, the boat can be recognized, the dummy can’t be seen. In the right image the scene is displayed in the visual spectrum with a monochrome ‘normal’ camera. Except of the navigation lights the image is black.
Figure 5: Image ‚normal‘ camera
The primary goal of the project is to realize a compact gated-viewing sensor based on technology available to the market. One of the main criteria is based on the cost efficiency to provide an affordable system for SAR. The sensor system is investigated in cooperation with the DGzRS in aspects of suitability and potential to find persons and floating objects in water.
Further central aspects of the project TRAGVIS are eye-safety, software and algorithm development, as well as complementary measurements of environmental and visibility conditions (e.g. aerosols) to characterize the system. In upcoming projects MAI, HUMAN and MUM further fields of applications, like the use of different (flying) platforms are examined. Next to the sight improvement over water, the usability of the gated-viewing technology is evaluated under water in the project SUBVIS.
In order to investigate the vision enhancement achieved with Gated-Viewing instruments we measure particle size distributions using a PALAS Fidas 200 S aerosol spectrometer. This data is primarily used to characterize TRAGVIS’ system performance under different environmental conditions. However, it is potentially interesting for different research fields as well (e.g. meteorology, environmental sciences), and we decided to share this data complimentary on demand. In case of interest, please use the contact information below to get in touch with us.