Space technology

Ice around Antarctica measured from the air

Two researchers are measuring the thickness of the ice in Antarctica using their advanced radar system. If field studies show that it works, the same method will be repeated on a satellite.

A propeller aircraft is sitting on the ice in Antarctica while being loaded. — The Basler plane is being prepared for departure and will, among other things, be loaded with the new radar system which is in the process of being tested. The wooden box contains the radar antenna. Photo: DTU

Monday 20 January 2025

Magnus Stenaa Jensen

The prop speed increases on the Basler aircraft. On board is the specially developed Polaris-radar and its inventors, the two expectant researchers Jørgen Dall and Anders Kusk. Soon, the plane will take off for a flight above Antarctica’s approx. 30 million cubic kilometres of ice.

“When I look out of the window, it’s just white, but on our radar it’s something else. Here, we get red and green shades showing that we can see through the ice and measure its thickness,” says Jørgen Dall, a professor at DTU Space.

Knowledge about the melting of the ice is crucial for being able to calculate the consequences of the ice melt. And this is precisely why the two researchers have embarked on a two-month climate mission in Antarctica.

The mission has been organized with support from the ESA (European Space Agency) Biomass mission, which so far has focused on mapping the uptake and emissions of CO₂ from the world’s forests using a satellite. Now, the researchers will investigate whether ESA’s satellite can also be used to monitor the ice in Antarctica, and they are therefore testing a DTU-developed radar system.

FACTS

ESA's Biomass mission

The Biomass satellite primarily focuses on providing completely new information about forest height and above-ground forest biomass from space, partly to better understand the state of the Earth’s forests and how they change over time, and partly to advance knowledge about the carbon cycle—including the uptake and emission of CO2. Biomass also has a secondary goal: to map the ice.

Holding back the ice

The Shackleton Ice Shelf lies about four hours away by plane from the researchers’ base, and stretches approx. 384 km along the east coast of Antarctica. The Shackleton Ice Shelf is one of the continent’s many so-called ice shelves, which act as an important protection against the melting of the Antarctic ice.

Ice shelves are large floating sheets of ice that extend from the coast of Antarctica, and play a crucial role in slowing the melting of the glaciers behind them. The ice shelves hold back the ice on land and thus prevent glaciers from sliding into the sea and melting. Therefore, the researchers are keeping a special eye on the ice shelves on their mission.

The view over Antarctica as seen from a plane. Photo: DTU — Monitoring how the glaciers move towards the sea and how the ice shelves on the continent help to slow down the movement is crucial to understanding the rise of the world's oceans. Photo: DTU

Unique radar system

DTU has a long history of developing radar systems and measuring the ice at the poles. Back in 1967, Professor Preben Gudmandsen from DTU and his team made the first radar measurements of the Greenland ice sheet.

Using a specially developed ice sounding radar, they were able to measure the thickness of the ice in the areas where they flew the radar over the ice. The results were essential for further climate research, and since then DTU has further developed radar systems for similar purposes.

“The Polaris radar which we conduct overflights with is a radar developed by DTU with support from ESA. It is unique because it can switch between two different radar modes, which—as far as I know—no other systems are able to do,” says Jørgen Dall.

The first Polaris radar mode is the ice sounding radar, which measures vertically down towards the ice beneath the aircraft, and is used to measure the thickness of the ice. The technology has its roots in Professor Gudmandsen’s measurements of the Greenland ice sheet.

The second mode is the synthetic aperture radar (SAR), which allows researchers to also map areas to either the right or left of the aircraft’s flight path. SAR thus creates detailed images of the surface of the ice.

Because Polaris can switch between the two radar functions, it gives researchers a unique opportunity to measure both the thickness of the ice as well as performing surface mapping on the same flight. In this way, the radar can also measure the so-called crystal orientation fabric (COF), which shows which direction ice crystals in glaciers and ice caps are facing.

When the crystals change direction under pressure, it affects how the ice flows. Therefore, measuring COF is important so that researchers can predict how the ice will flow when temperatures rise, and gain knowledge about which areas should be studied further, for example by means of boreholes.

Radar image of Antarctica captured during a flyover. Photo: DTU — The coast of Antarctica as seen through the radar. Photo: DTU

Future still uncertain

“It’s not certain that we’ll be able to make an elevation map of the bottom of the ice shelves with the Biomass satellite, as there are several complications right now. Among other things, the satellite only flies over the ice every nine months, so a long time passes before we have fresh data. On the other hand, there is a good chance that the satellite can measure ice speeds,” says Jørgen Dall.

Measuring ice speed enables you to see how fast the ice is moving towards the sea. In some places, it has been difficult to measure the ice movements with existing satellites because the movements are so small. However, the hope is that the Biomass satellite will be able to detect these movements.

A violent storm is gathering over Antarctica, and the researchers are therefore facing the prospect of four cancellations and an eight-day delay before they can finally head back to DTU. Now, they will analyse the collected data until late 2025, and provide ESA with feedback on whether the radar technologies can be used in ESA’s Biomass satellite in the future.

Contact

Jørgen Dall Professor Phone: +45 45253842 jdall@dtu.dk

Anders Kusk Research Engineer Phone: +45 45253832 akusk@dtu.dk