- Detecting whales, protecting whales
Human activities often have an intrusive effect on nature – whether we build suburbs on formerly forested lands or pollute streams with factory runoff, the things we do affect the world’s other inhabitants. But a small group is looking to mitigate the impact of some human activities on the largest of our neighbors: whales.
Noise pollution resulting from maritime activities such as pile driving during wind farm construction and airgun use in the search for oil and gas have been implicated in whale stranding events. There are even noise-mitigation regulations stipulating that workers must stop these activities when whales are spotted nearby.
But how can anyone be sure a whale is out there? “Whoever has looked at the sea for any length of time knows how quickly the eyes get tired and concentration dwindles,” said physicist Daniel P. Zitterbart of the Alfred Wegener Institute (AWI), which conducts geophysical surveys using loud sound sources. “In addition, we cannot look in all directions at the same time – and at night, we virtually see nothing.”
The FIRSTnavy thermal imager, mounted on the research ship Polarstern, is used to detect whales in order to protect them from noise pollution. Courtesy of Lars Kindermann, Alfred Wegener Institute.
Accurate whale detection would help maritime work crews comply with the regulations. So Zitterbart and colleagues at the AWI Helmholtz Centre for Polar and Marine Research in Germany developed a ship-based automatic thermal imaging system that can detect large whales, day or night, from distances up to 5 km. It spots whale spouts as animals surface for air – and detects significantly more whales than researchers using binoculars to spot the animals, the scientists reported in a recent paper.
“In contrast to most detection systems, we look for signals which are almost never there, because whale blows are
very faint and short signatures,” Zitterbart said. “The main task was therefore to keep the false-positives to a minimum,
so that the operator is not frustrated.”
The researchers mounted a FIRSTnavy IR camera from Rheinmetall Defence Electronics GmbH of Bremen, Germany, in the crow’s nest of the research vessel Polarstern for tests on expeditions in polar and subpolar regions. They found that it overcame the problem of observer fatigue and worked in various sea conditions; they now plan to test the system in warmer waters.
The system includes a stabilization gimbal and a workstation that does computer vision data processing. The thermal sensor detects differences in temperature of less than one-hundredth of a degree Celsius. The IR device produces five thermographic 360° images per second of the ship’s surroundings. The image size is 7200 × 576 pixels, and the sensor head rotates at 5 rps. The system can endure harsh conditions including gale-force winds and temperatures down to –30° C.
Software analyzes the raw video for thermal whale spout signatures. “A whale spout is bright on the thermal image and then becomes darker again in a very specific pattern,” Zitterbart said. The spout appears lighter because it is significantly warmer than the sea surface, at least in the subpolar or polar regions, he noted.
The effects of noise on marine mammals are not fully understood, Zitterbart said, “but we wanted to do everything possible to protect the whales.”
The study appears in PLOS ONE (doi: 10.1371/journal.pone.0071217).
MORE FROM PHOTONICS MEDIA