Now we have the perfect prescription

New technologies can often mean a quantum leap for research – especially in difficult areas like glacier research, where scientists often have to work with ice streams and ice sheets measuring up to four kilometres thick. Last year, glaciologists from the Alfred Wegener Institute achieved just such a quantum leap: with the aid of the AWI’s new ultra-wideband ice radar, they can now aerially scan glaciers and ice sheets from top to bottom. In the following interview, Division Head Prof Angelika Humbert and ice-radar expert Dr Tobias Binder explain how this technology works, and what insights they hope to glean with its help.

Ms Humbert, Mr Binder: Over the past few months, you’ve tested the new ice radar in Greenland and in a measuring campaign in the Antarctic. Are you satisfied with the results?

Angelika Humbert: We’re thrilled; the new ultra-wideband ice radar produces datasets with significantly higher resolution than its predecessor. That means, for instance, that we can now see a glacier’s layers and bends, or identify deep fissures we couldn’t see with the old equipment. When we look at the data now, it feels like we finally have eyeglasses with the perfect prescription, because we can now actually see all of these contours in the ice.

Tobias Binder: What’s most impressive is the depth of resolution. When we took measurements with the old system, there was often a data-free zone a few hundred metres above the bedrock where we couldn’t see a thing. With the new radar, for roughly 95 percent of the regions we’ve surveyed in Greenland we can recognise not only the topographical details of the rock under the ice sheet, but also the characteristics of the first ice layers above it. In other words, we can look all the way through the glacier, which gives us wholly new insights and a chance to better understand important mechanisms like the flow of ice. 

Okay, for us non-experts: how does the new ice radar actually work?

Tobias Binder: Our ice radar basically works the same as any other radar: it sends out radio waves at regular intervals. They are reflected back from the ice and the ground beneath it, and picked up by the system. The radar then calculates how much time has passed between transmitting the waves and receiving them back – and that tells us the distance. Since the waves’ reach varies with the type of ice, we ultimately end up with a steady flow of information from different depths. Thanks to its 24 receiving channels, the new radar can also pick up reflections from different directions, which allows us to match the signals to their respective directions, and to much more accurately depict bedrock topography.

Angelika Humbert: Unlike conventional radar used in aircraft and ships, which transmits radio waves at a fixed frequency, our new ultra-wideband ice radar covers a whole range of frequencies: it transmits radio waves with frequencies from 150 to 600 Megahertz and can receive the reflections on 24 channels; the old system only had one receiving channel. This flexibility ensures we receive high-resolution data. However, it also means that, in one hour of flying, the new radar records up to 2.5 terabytes of data – which is more than we documented with the old radar in the course of an entire Antarctic campaign. As such, we’re now gaining our first experience with Big Data in glacier research.

What new insights into glaciers and ice sheets did you gain in the first aerial campaigns with the new radar?

Angelika Humbert: In the summer of 2016, we flew transects over Greenland’s 79° North Glacier and monitored the ice’s typical course for 200 kilometres – in other words, from the inland ice we followed the glacier to the grounding line. That’s what we call the point where the glacier flows into the sea and its tongue no longer touches the ground. We then took a look at the glacier’s inner structure and analysed the topography of the ground below the ice stream. The roughness of this surface is a key factor in computer models of the 79° North Glacier’s flow, since our goal is to make predictions as to whether, and if so, how much, its flow speed will increase due to climate change. Today, this glacier is one of the few Greenlandic ice streams that have retained their floating tongue.

Tobias Binder: Unfortunately, we couldn’t make many flights in the Antarctic this summer. Given its various components, the new system is fairly heavy, which is why the measuring flights are now 500 kilometres shorter than with the old, lighter radar. That being said, we had sufficient range to reach Kohnen Station on the Antarctic inland ice plateau and measure the ice near the station, which is up to 2,780 metres thick. Until then, we had no high-resolution on the bottommost ice layer for this part of the Antarctic Ice Sheet. The data analysis, which we’ll begin in the next few weeks, will tell us whether or not the new radar produces better results and new insights.

Angelika Humbert: Being able to use the new ice radar in both the Arctic and Antarctic so soon posed tremendous challenges for our colleagues at AWI Logistics, especially since the equipment is so heavy. Without the outstanding work of our colleagues on the AWI Flight Team, we researchers wouldn’t have a single dataset – so we’d like to express our heartfelt thanks!

The interview was conducted by Sina Löschke.