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Series thermal imaging camera were mounted on a tripod next to the bridge of an ice strengthened vessel traversing Greenland’s ice filled waters to deliver fuel to its remote settlements. In this extreme environment, arguably one of the most dangerous maritime areas in the world with its floating chunks of years old dense glacier ice, FLIR’s thermal imaging cameras were put to the test.
Thermal imaging detects ice in all sizes and shapes During the test thermal imaging cameras were successfully used to detect pieces of ice of different sizes and shapes. These are generally divided into three categories: icebergs, bergy bits and growlers. Icebergs are floating chunks of ice with more than 5 metres of its height exposed above sea level. Bergy bits are pieces of icebergs showing 1 to 5 metres above sea level. Growlers are pieces of icebergs showing less than 1 metre above sea level. With the thermal imaging camera all of those three categories were detected. Due to their size icebergs are usually relatively easy to detect by radar. In most occasions using radar should suffice in detecting them. The bergy bits are smaller than full-grown icebergs, making them harder to detect, both by radar and visually.
Growlers, being the smallest category, are the most difficult form of ice to detect both visually and on radar. Though small, growlers can still pose a serious threat even for ice strengthened vessels.
Avoiding damage and saving fuel
Even the hull of ice strengthened vessels can be damaged in case of a collision with a multi-year ice growler. Also the fuel consumption of a vessel is higher if it is slowed down due to the impact of such collisions. It is therefore much safer and more efficient to avoid all growlers and bergy bits. Growlers can easily be obscured by the sea clutter on the radar screen, especially if they have a smooth relief that deflects radar energy away from the antennae. In clear conditions it may be possible to detect growlers visually, but at night and in bad weather that becomes increasingly difficult. Governmental authorities warn seafarers that traverse Arctic waters not to trust on radar alone to detect icebergs, bergy bits and growlers in fog and darkness. Given the fact that the force of impact in case of collision varies as the square of the speed the authorities advise to lower the speed of the vessel.
Detecting ice with thermal imaging
Thermal imaging cameras can be used to detect ice because the ice is generally much colder than the surrounding ocean. Not only do the temperatures of the ice and the seawater differ, in most cases there is also a difference in emissivity. Emissivity can be described as the ability of a material to emit energy by radiation, more specifically the ability to emit thermal radiation. Two objects at the same temperature but with different emissivity will present different levels thermal radiance to the thermal imaging camera. Most of the ice in the sea surrounding Greenland originates from glaciers and therefore mostly consists of fresh water. The exact emissivity differs slightly depending on the circumstances, but generally speaking fresh water has a higher emissivity than the salty sea water. This means that even if the temperature of the ice and the
seawater are the same temperature, there will still be a contrast between the two in the thermal image.
FLIR M-Series thermal imaging camera
The FLIR M-Series thermal imaging camera is available with a variety of sensors and resolutions to meet a wide range of maritime needs. For the ice detection test the models M-612L and M- 625L were used. Both of these models include a thermal imaging camera with an uncooled Vanadium Oxide (VOx) microbolometer detector that produces thermal images at a resolution of 640x480 pixels and a 100 μlx Lowlight CCD camera, mounted in a rugged waterproof housing capable of 360° pan and +/-90° tilt that is waterproof and contains internal heating to ensure its performance even in such cold environments as the Arctic. The difference between the two is the optics and resulting field of view.
The lens of the M-625L gives it a field of view of 25° × 20°. Although this gives an excellent situational awareness, the range performance is better with a narrower field of view. The M-612L has a field of view of 12° x 10°, which is narrower, allowing for a better range performance. In average conditions the thermal imaging camera incorporated in
the M-625L is capable of detecting a small vessel (2.3 m × 2.3 m) at a distance of over 2 kilometres (over 1 nautical mile). The M-612L’s thermal imaging camera can be used to detect the same size target at a distance of over 3 kilometres (over 1.7 nautical miles). The test conclusively showed that thermal imaging cameras are able to detect bergy bits of similar size in real life situations from roughly equivalent distances, despite snowfall reducing their range performance. This makes FLIR thermal imaging cameras an ideal addition to conventional ice detection tools, filling in the gaps where radar and searchlight underperform.
Man overboard
In the crisp high contrast thermal images the smallest of details are shown, regardless of lighting. This not only allows these thermal imaging cameras to aid the captain and navigators with ice detection, it can also prove invaluable in man overboard situations. The large temperature contrast between the cold water and the warm person allows the camera operator to swiftly locate the waterborne person regardless of lighting..
Installing a FLIR thermal imaging camera on vessels traversing Arctic waters will help avoid collisions, increase efficiency and help safeguard the safety of the crew in case of man overboard situations regardless of lighting conditions and in all types of weather.
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