Washington, Jan 25 (IANS): Using ice-penetrating radar data, NASA scientists have built the first-ever comprehensive map of layers deep inside the Greenland ice sheet.

This new map, prepared on the basis of data collected by NASA's Operation IceBridge and earlier airborne campaigns, allows scientists to determine the age of large swaths of Greenland's ice.

"This new, huge data volume records how the ice sheet evolved and how it's flowing today," said Joe MacGregor, glaciologist at the University of Texas at Austin and the study's lead author.

Greenland's ice sheet is the second largest mass of ice on Earth, containing enough water to raise ocean levels by about 20 feet.

The ice sheet has been losing mass over the past two decades and warming temperatures will mean more losses for Greenland.

Scientists are studying ice from different climate periods in the past to better understand how the ice sheet might respond in the future.

Ice-penetrating radar works by sending radar signals into the ice and recording the strength and return time of reflected signals.

From those signals, scientists can detect the ice surface, sub-ice bedrock and layers within the ice.

"IceBridge surveyed previously unexplored parts of the Greenland Ice Sheet and did it using state-of-the-art CReSIS radars," said Mark Fahnestock, glaciologist from the Geophysical Institute at University of Alaska Fairbanks.

IceBridge's flight lines often intersect ice core sites where other scientists have analyzed the ice's chemical composition to map and date layers in the ice.

This information will be helpful for evaluating the more sophisticated ice sheet models that are crucial for projecting Greenland's future contribution to sea-level rise.

This study appeared online in the Journal of Geophysical Research Earth Surface.