Ice spy: radar picks up Antarctic melting

17 October 2006

Hi-tech radar has revealed the first accurate picture of Antarctica's ice-shelf health. Polar scientists say the new measurements tell them how quickly Antarctica is responding to climate change and what this means for global sea levels.

Antenna investigates...

Ice shelves stretch out from the edge of the land to float on the sea.

Image: British Antarctic Survey

Antarctica is so cold that its coastline is surrounded by vast 'shelves' of floating ice. In places these ice shelves are over a kilometre thick.
Ice shelves are important because they help to hold Antarctica's icecap in place and stop glaciers from flowing into the sea. If the ice shelves ever melted away completely, land-locked ice would be set free, causing sea levels to shoot up.

Broadband Version

Have a look at what the scientists see as they fly over an ice shelf.

Video: British Antarctic Survey

An ice block twice the size of Greater London broke away from the Larsen B ice shelf in 2002.

Image: NASA GSFC

While some ice shelves in the Antarctic seem stable, others are suffering, and every year big chunks crash into the sea. Most scientists think this is happening because the Earth is getting warmer as the amount of greenhouse gases in the atmosphere increases.
Until now, figuring out how much ice was melting involved quite a bit of guesswork, but now scientists at the British Antarctic Survey have developed a new type of radar that can help. It's let them see exactly what's happening both inside and at the bottom of the ice shelf for the first time.
How does the radar work?
The technology is a more accurate version of the systems used by planes and ships to detect objects in their path. This new 'phase-sensitive' radar detects the internal structure and looks at the bottom of the ice, so researchers can see whether it's melting or staying put.

The F-16 fighter jet uses radar to locate military targets.

Image: Freefoto.com

The radar kit has two antennas - one which beams radio waves down through the ice and another which collects the signal when it bounces back up off the bottom. The time it takes between sending and receiving this signal is converted into a distance, giving scientists the exact thickness of the ice shelf.
The radar doesn't only measure distance though - it can also reveal ice density patterns. These measurements are crucial because they reveal how the more fluffy layers at the top are gradually compressed to form solid ice. Changes in this compression process will also cause changes in the thickness of the ice shelf.

Using the radar in front of Vinson Massif, the highest Antarctic mountain.

Image: British Antarctic Survey

'Internal layers in ice have been mapped before, but now we have the first accurate measurements of how fast the layers are changing in relation to each other.
'We started using the radar five years ago to measure how fast the structure of the ice is changing. It was a surprise to get so much information from it, because when we first set out, we had no idea just how much detail we would see within the ice.'
Adrian Jenkins, polar scientist, British Antarctic Survey

Adrian (right) and his field assistant Crispin Day outside their tent.

Image: British Antarctic Survey

Adrian controls the radar from a screen and keyboard on top of the box.

Image: British Antarctic Survey

To protect the kit against the elements it's insulated in a temperature-controlled box. Once they've finished measuring, the scientists mark each spot with bamboo stakes, so they can come back later to see if the ice's thickness has changed.

The scientists have spent several months working on the ice shelf.

Image: British Antarctic Survey

So far the polar scientists have only used the radar to measure the Filchner-Ronne Ice Shelf, an enormous block of ice twice the size of Great Britain. Here, they've found that ice from snow or glaciers continually replaces ice being melted from the bottom by sea water.
But while this part of Antarctica isn't going anywhere fast, other areas tell a very different story. Scientists think it's important to figure out why some ice shelves are changing and others, such as the Filcher-Ronne, aren't.
'Several of the smaller ice shelves around the Antarctic Peninsula have disintegrated recently.
'High-accuracy measurements of the behaviour of much larger ice shelves such as the Filchner-Ronne are of importance to our understanding of how these bigger systems may react to future environmental change.'
Julian Dowdeswell, Director, Scott Polar Research Institute

Julian Dowdeswell, Director, Scott Polar Research Institute

Image: Scott Polar Research Institute

The next place to take the radar could be the Larsen Ice Shelf, which polar scientists are worried about - enormous bits of it have collapsed in recent years.
'It might be melting away, or the upper layers could just be getting denser - the radar will tell us. There's so much future potential for this technology and what it will help us to understand.'
Adrian Jenkins

Cracks like this are appearing in ice shelves in ever greater numbers.

Image: Michael Van Woert, NOAA NESDIS, ORA

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