Featured Research

from universities, journals, and other organizations

Airborne radar looking through thick ice during NASA polar campaigns

Date:
December 2, 2013
Source:
NASA/Goddard Space Flight Center
Summary:
The bedrock hidden beneath the thick ice sheets covering Greenland and Antarctica has intrigued researchers for years. Scientists are interested in how the shape of this hidden terrain affects how ice moves -- a key factor in making predictions about the future of these massive ice reservoirs and their contribution to sea level rise in a changing climate.

A MCoRDS’s underwing radar antenna arrays mounted beneath the wing of NASA’s P-3 aircraft at McMurdo Station’s airfield. MCoRDS uses arrays beneath the wings and fuselage of the plane, giving a total of 15 antennas that can send and receive signals used to map polar ice and bedrock.
Credit: NASA/George Hale

The bedrock hidden beneath the thick ice sheets covering Greenland and Antarctica has intrigued researchers for years. Scientists are interested in how the shape of this hidden terrain affects how ice moves -- a key factor in making predictions about the future of these massive ice reservoirs and their contribution to sea level rise in a changing climate.

NASA has been monitoring Antarctic and Arctic ice since 2009 with the Operation IceBridge airborne mission. Although the primary objective is to continue the data record of ice sheet surface elevation changes from NASA's Ice, Cloud and Land Elevation Satellite, or ICESat, which stopped functioning in 2009, IceBridge is also gathering data on other aspects of polar ice from snow on top to the bedrock below. One radar instrument on these flights that is currently headed to Antarctica for another year of observations is revealing insights about the bedrock hidden beneath the ice sheet.

IceBridge is carrying a suite of radar instruments designed, built and operated by scientists, engineers and university students with the Center for the Remote Sensing of Ice Sheets (CReSIS), a National Science Foundation-funded center based at the University of Kansas.

This bedrock-mapping radar is known as the Multichannel Coherent Radar Depth Sounder or MCoRDS. MCoRDS measures ice thickness and maps sub-glacial rock by sending radar waves down through thick polar ice. This ice-penetrating radar is the result of efforts that started with a collaboration between NASA and the National Science Foundation 20 years ago.

In the early 1980s, researchers started showing interest in using radar to measure ice thickness and map sub-ice rock. Among the interested was NSF's Office of Polar Programs, which provided the initial funding for a thickness-measuring instrument. "We were given one year to prove it would work," said Prasad Gogineni, scientist at CReSIS. CReSIS researchers used that funding to build their first radar depth sounder, which started flying aboard NASA aircraft in 1993. Over the years, CReSIS has built a number of instruments -- each more advanced that the last -- leading to the radar IceBridge relies on today.

Through the Ice

One of the biggest obstacles faced when building an ice-penetrating instrument like MCoRDS is the nature of radar itself. Radar works by sending out radio waves and timing how long it takes for them to reflect back. Radio waves travel through air virtually unimpeded, but materials like metal, rock and water act almost as mirrors.

Ice, on the other hand reacts differently depending on the radar's frequency. It reflects high-frequency radio waves, but despite being solid, lower frequency radar can pass through ice to some degree. This is why MCoRDS uses a relatively low frequency -- between 120 and 240 MHz. This allows the instrument to detect the ice surface, internal layers of the ice and the bedrock below. "To sound the bottom of ice you have to use a lower frequency," said John Paden, CReSIS scientist. "Too high a frequency and signal will be lost in the ice."

These radio waves are sent out in rapid pulses through an array of downward-pointing antennas mounted beneath the aircraft. This array of multiple antennas, up to 15 on NASA's P-3, allows researchers to survey a larger area and record several signals at once to get a clearer picture.

The 15 element array is the largest ever flown on the P-3 and is was built as part of a joint effort between NASA, the University of Kansas and private industry. The design and construction of this array, much of which was done by University of Kansas undergraduate and graduate students, took about six months.

Radar pulses travel down to the surface, through the ice to bedrock below and back up through the ice to MCoRDS's array, where they are routed to the instrument's receiver and recorded on solid state drives aboard the aircraft.

Each survey flight yields a great deal of data, often as much as two terabytes, that then needs to be downloaded, archived and backed up. The computing infrastructure needed to handle this data is managed by people from the University of Indiana, which is also a partnering organization in CReSIS. During each campaign, University of Indiana personnel support the mission by staying up through the night to ensure that the data collected each day is successfully stored and backed up.

Processing Pictures

After returning from an IceBridge campaign, CReSIS researchers spend months processing the archived data to build a detailed view of ice sheets and bedrock. First, researchers tease out the return signals from the ice surface and bed. Because thick ice attenuates, or weakens, radar so researchers need to filter the data to pick out the weak return signal from the bed, which would otherwise be drowned out by the much stronger surface return and any noise in the data.

After finding the ice surface and bedrock, researchers use something called synthetic aperture radar processing. This combines many readings from a radar antenna as it moves over the surface researchers can create a large simulated array. "You can make an aperture one kilometer long by moving the radar one kilometer," said Paden. As with camera lenses, bigger is better, and a larger array lets researchers see more detail.

This sort of processing yields a detailed, but narrow, swath of the ice and sub-ice terrain for each antenna. Building a wider view is more complicated than just combining these separate signals. Although MCoRDS records signals coming back from the left and right of the plane's flight path, it cannot determine which side the signals are coming from. To overcome this, CReSIS researchers use something known as tomography, a technique that uses specialized computer software to calculate the position and distance of signals returned from the bedrock. Once researchers can tell where terrain features are relative to the array they can combine the several channels to build a swath of terrain data useful for creating three-dimensional representations of the bedrock.

The Road Ahead

These terrain data are helping scientists better understand what's under ice sheets. In the past year, researchers have produced new maps of Greenland's and Antarctica's bedrock and discovered a large and previously undetected canyon under Greenland's ice sheet. Better information on sub-ice terrain will help researchers develop the next-generation ice sheet models needed to project future changes to glaciers, and better understand the flow of water at ice sheet bases.

As IceBridge continues to add to the record of sub-ice terrain measurements through its surveys over Greenland and Antarctica, scientists, engineers and students at CReSIS will keep making more advances. Improvements such as larger antenna arrays and improved data-processing techniques promise to make radar depth sounding even more effective. And in the future, uninhabited aerial vehicles like NASA's Global Hawk, could greatly increase the amount of terrain that can be covered from the air.

Exactly what the future holds remains to be seen, but researchers have made great strides in probing polar ice thanks to a decision made by one person, former NASA program manager Bob Thomas, who provided Gogineni and his team the opportunity to prove that their instrument worked and funding from NASA's PARCA initiative. "Without that, we would not have a depth sounder and imager program at KU," said Gogineni. "It took both agencies to make it to the stage we are today."


Story Source:

The above story is based on materials provided by NASA/Goddard Space Flight Center. Note: Materials may be edited for content and length.


Cite This Page:

NASA/Goddard Space Flight Center. "Airborne radar looking through thick ice during NASA polar campaigns." ScienceDaily. ScienceDaily, 2 December 2013. <www.sciencedaily.com/releases/2013/12/131202172019.htm>.
NASA/Goddard Space Flight Center. (2013, December 2). Airborne radar looking through thick ice during NASA polar campaigns. ScienceDaily. Retrieved April 17, 2014 from www.sciencedaily.com/releases/2013/12/131202172019.htm
NASA/Goddard Space Flight Center. "Airborne radar looking through thick ice during NASA polar campaigns." ScienceDaily. www.sciencedaily.com/releases/2013/12/131202172019.htm (accessed April 17, 2014).

Share This



More Earth & Climate News

Thursday, April 17, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

The Great British Farmland Boom

The Great British Farmland Boom

Reuters - Business Video Online (Apr. 17, 2014) Britain's troubled Co-operative Group is preparing to cash in on nearly 18,000 acres of farmland in one of the biggest UK land sales in decades. As Ivor Bennett reports, the market timing couldn't be better, with farmland prices soaring over 270 percent in the last 10 years. Video provided by Reuters
Powered by NewsLook.com
Small Reactors Could Be Future of Nuclear Energy

Small Reactors Could Be Future of Nuclear Energy

AP (Apr. 17, 2014) After the Fukushima nuclear disaster, the industry fell under intense scrutiny. Now, small underground nuclear power plants are being considered as the possible future of the nuclear energy. (April 17) Video provided by AP
Powered by NewsLook.com
Change of Diet Helps Crocodile Business

Change of Diet Helps Crocodile Business

Reuters - Business Video Online (Apr. 16, 2014) Crocodile farming has been a challenge in Zimbabwe in recent years do the economic collapse and the financial crisis. But as Ciara Sutton reports one of Europe's biggest suppliers of skins to the luxury market has come up with an unusual survival strategy - vegetarian food. Video provided by Reuters
Powered by NewsLook.com
How Mt. Everest Helped Scientists Research Diabetes

How Mt. Everest Helped Scientists Research Diabetes

Newsy (Apr. 15, 2014) British researchers were able to use Mount Everest's low altitudes to study insulin resistance. They hope to find ways to treat diabetes. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins