Radar reveals Greenland bedrock
Antennas developed by Swiss scientists have sounded ice layers in Antarctica up to several kilometres thick, as well as the rocks underneath.
This is of interest not only to geologists and climatologists attempting to measure the effects of global warming on Earth’s ice-covered regions, but also to astronomers with an eye on lunar or Martian ice caps.
Attached to a plane, high-precision antennas designed at the Federal Institute of Technology in Lausanne (EPFL) can analyse with unprecedented precision the composition of an ice layer nearly three kilometres thick, as well as the depth of the underlying bedrock.
Creating these high-tech antennas is part of a wide-ranging project known as the Polaris (Polarimetric Airborne Radar Ice Sounder) program, launched by the European Space Agency (ESA) and run by the Technical University of Denmark.
Juan Mosig, head of EPFL’s electromagnetics and acoustics laboratory, which manufactured the antennas, told swissinfo.ch they had initially considered testing the equipment on the Aletsch glacier, the largest glacier in the Alps, in canton Valais.
But he said Swiss regulations mean it’s a very complicated and lengthy process getting permission to make such flights.
The Danes then suggested Greenland – “but even there it’s hardly a piece of cake,” he said.
“With the antennas [which measure eight metres by 50 centimetres and weigh 40kg] strapped to the fuselage the planes basically had an extra aileron, which made flying more tricky. It certainly wasn’t for beginners.”
Not to mention temperatures which could drop beneath minus 50 degrees Celsius and icy runways which caused wicked vibrations when taking off and landing – in short, conditions that weren’t dissimilar to launching something into space. (See box to learn how the radar works.)
Astronomers are also rubbing their hands. If the tests carried out in winter in Greenland and this spring in Antarctica prove conclusive, the next step will be to attach the antennas to a satellite to analyse the Earth’s entire ice layer from outer space.
Eventually, ESA even aims to use the technology to study the different ice types present on Mars or on the moons of Jupiter and Saturn.
While the ice at the bottom of lunar craters is made of water, that found at the poles of Mars is a mix of frozen water and dry ice, the solid form of carbon dioxide.
After the success of Nasa’s Cassini-Huygens mission to Saturn and Saturn’s largest satellite Titan, which resulted in a probe landing on the surface of Titan, scientists want to send more machines back to a place that could teach us a lot about our own origins – if scientists can look beneath the ice.
Back on Earth, no complete map exists of the bedrock underneath the ice caps. Mosig says satellites images are imprecise – “and it’s not as if we can go drilling and remove ice cores every 100 metres”.
The inventors of the radar which “looks under the ice” will present the preliminary results of the Antarctic expedition at the 11th International Symposium on Antarctic Earth Sciences in Edinburgh from July 10-16.
“There will be climatologists, geologists and other scientists who’ll definitely be interested in what we’re going to say,” Mosig said.
He added that there could also be scientific institutions or international organisations that would come up with funds so the “cute little contraption” could be used for map making.
“There are also sci-fi fans who are hoping we’ll uncover the buried city of Atlantis – or a herd of frozen dinosaurs,” said Mosig, who didn’t make a big secret of the fact that science fiction had a big influence on him when he was young, “like many scientists”.
How it works
Fixed into the lower part of the fuselage, the eight antennas form a radar with a wide aperture, capable of high-precision detection.
The antennas generate electromagnetic waves at a frequency of 450 MegaHertz (MHz) that are in the UHF (ultra-high frequencies) band, similar to the waves of traditional televisions.
“Depending on its frequency, a wave can either pass through a substance or be absorbed by it,” said Juan Mosig. “UHF waves are the most suitable for this type of project because they easily penetrate the ice.”
Every time a change occurs in the property of the ice, a part of the wave ricochets, returning a faint echo that is picked up by the antenna. This echo is much stronger when the wave reaches the bedrock.
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