Measuring land and sea ice thickness
Land ice is freshwater ice that covers the land area of Antarctica. Sea ice is frozen seawater. Every winter, Antarctica doubles in area because of an increase in sea ice!
Measuring the thickness of land and sea ice and how quickly these thicknesses change allows scientists to make more accurate predictions about future changes in Antarctica. The data is also used to inform climate models.
There’s a lot of ice in Antarctica. The average thickness of land ice – the Antarctic ice sheet – is 2.16 km. That’s very deep – too deep to drill – so scientists use satellites instead.
Measuring the thickness of sea ice is more complicated as salt interferes with the radar waves. University of Canterbury’s Professor Wolfgang Rack explains how his team uses electromagnetic induction to overcome this issue.
Questions for discussion
Why do you think the EM bird needs to be as close to the sea ice as possible?
Why do you think the scientists use a helicopter instead of a PistenBully or other form of land transport?
Transcript
Professor Wolfgang Rack
On the helicopter, we are using an instrument, which we call EM bird, and the EM stands for electromagnetic induction. We cannot use radar instruments to measure the sea ice thickness because there is still some salt in the sea ice, which effectively absorbs the radar wave.
So the EM bird works with a different technology. It’s electromagnetic induction, and this means that this instrument emits a magnetic field, and this magnetic field can trigger a very small electric current in the seawater. And this very small electric current induces a secondary magnetic field, and this is what we measure. And this magnetic field is related to the distance between the instrument and the seawater.
So the EM bird is the only remote-sensing instrument which can measure sea ice thickness directly. It hangs under a helicopter, and it needs to be as close to the surface as possible.
Acknowledgements
Professor Wolfgang Rack, University of Canterbury
Stills and footage of chopper and EM bird in Antarctica, courtesy of Wolfgang Rack
