What's hidden under Greenland ice?
Ice has covered Greenland for millions of years. So what's hidden under this ice cap? Mountains and valleys? Rivers and lakes? Of course, we might know it sooner than we would have liked if the ice covering Greenland continues to melt. But researchers from Ohio State University have decided that they wanted to know it next year and have developed a radar to reveal views of land beneath polar ice. Their first tests of this new radar, which helps them to catch 3-D images of the ground under the ice, took place in May 2006. The next images will be shot in April 2007.
But what exactly these researchers are trying to achieve?
As scientists try to gauge the effects of global climate change, they are beginning to look very closely at conditions beneath Earth's ice sheets, which cover roughly 15 percent of the planet. Earth's poles have been covered in ice for 2.7 million years. Scientists suspect that, just as the ice surface has changed over that time, a different world has evolved underneath.
"One of the key things we need to know to predict how the ice sheet is going to change in the future is the distribution -- and the change in distribution -- of sub-glacial water," said Ken Jezek, professor of earth sciences at Ohio State. "So our dream is to create this new image of what Greenland would look like, were the ice sheets stripped away."
And this is what they want to achieve with the Global Ice Sheet Mapping Orbiter (GISMO). Here is what they did.
Jezek and the GISMO team acquired the first effectively three-dimensional image of the ground -- in a strip about a mile wide, 1.2 miles beneath the ice. They were able to do so because GISMO features multiple, electronically steerable antennas which operate while the airplane is flying, coupled with special processing algorithms.
Below is a picture of the multiple antennas of GISMO (Credit: Ohio State University). Here is a link to a larger version.
And below is an illustration of how GISMO was used. The researchers have used the interference between different radar signals to reveal the land beneath the ice in Greenland. Below is a GISMO interferogram: "The interference pattern resembles the rainbow effect on an oily puddle" (Credit: Ohio State University). Here is a link to a larger version of this image.
Next year, GISMO will continue to be used in Greenland. But the researchers think that their radar device might be used one day by satellites. Why would it be impossible to look under Martian ice caps afetr all? Except that the instruments would be sent to Mars :-)
For more information about GISMO, you can read this technical paper, "Glaciers and Ice Sheets Mapping Orbiter Concept (PDF format, 4 pages, 135 KB).
Sources: Ohio State University news release, December 11, 2006; and various websites
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