THERMAL INFRARED RADIATION FROM FREE LIVING WHALES

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ABSTRACT

As part of a search for new detection techniques, and for obtaining information on whale surface temperatures, an Agema Thermovision 880 thermal imaging system was used to detect thermal infrared radiation from whales. The study took place along the northern coast of Norway and the northwest coast of Svalbard (68° to 80° N latitude). The emphasis of the study was on minke whales, but humpback, fin, blue and sperm whales were also observed. The apparent radiation temperature was strongly dependent on sea conditions, signal angle, and atmospheric interference; detection depended thus upon weather. During the study, sea surface temperatures varied as much as 7°C but the sea and minke whale body trunk surfaces were usually within 0.0° to 0.1°C of each other. The other species observed had temperature differences of 0.0° to 1.0°C relative to the sea surface. Temperature differences between sea water and whale appendages ranged from 0.0° to 6.0°C. The indicated maximum difference between sea water and blow (i.e., expired air) was 4.0°;C, while the maximum difference for the blowhole was 4.1°C. The results from all whales observed support the belief that the main body trunk is normally not a heat window, this function being reserved for the appendages. However, the results also indicate a regulated dermal blood flow determining heat loss from the body trunk. Detection of whales by thermal infrared radiation from the body trunk appears unreliable; in contrast, the blow and blowhole provided a consistent positive signal with apparent temperature differences to the surroundings ranging from 0.2° to 4.1°C.

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