Today, sea ice offers one of the most important ways for measuring climate change, as the fate of the ice is directly dependent on global warming. By combining satellite data on the expanse of polar ice with information on the ice’s thickness, it is possible to roughly estimate the total amount of ice – and gain valuable insights on the status quo and development of the global climate. The EM-Bird helps researchers do so.
As the EM-Bird glides over the ice, it measures how high it is above the ice-water boundary – i.e., how high it is over the ice underside. At the same time an integrated laser measures how high the torpedo is over the surface of the ice – the distance to the ground. By comparing the two measurements, the EM-Bird’s onboard computer can then calculate the thickness of the ice. Since the helicopter’s metal hull would throw off the readings, the device has to be suspended from a cable.
The AWI’s sea-ice physicists have been using the EM-Bird since 2001. In a typical Polarstern expedition, one of the onboard helicopters flies up to 40 nautical miles away from the mother vessel before deploying the device over the ice. Since the EM-Bird makes ten measurements per second, each flight yields a wealth of data. For the past several years, the AWI’s two polar research planes have also carried out land-based measuring flights – taking off from Svalbard or the coast of Canada, for example. Their EM-Bird flights can range up to 350 nautical miles. During take-offs and landings, the EM-Bird is safely stowed in a brace mounted on the hull; it is only lowered with a winch once the plane is airborne.
One limitation of the electromagnetic induction system used by the EM-Bird is that it can’t differentiate between snow and ice, since both layers are largely electrically nonconductive. But more can be learned by additionally consulting the information provided by the laser. The laser measures both the height of the snow and that of the ice above the water’s surface, referred to as the freeboard. That being said, the laser can’t penetrate the water below. “The EM-Bird can tell us the total thickness of snow and ice, while the laser gives us the freeboard. By combining the two, we can arrive at much better estimates of the actual thickness,” says Stefan Hendricks with a certain degree of pride. “We’re currently one of only very few research groups in the world to use both techniques in the same aircraft.” Accordingly, the researchers are happy to share their data on international sea-ice portals. “Above all, we also conduct basic research intended to help better understand sea-ice formation, and especially the effects of climate change, in the future,” says Stefan Hendricks.