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Keith Koehler               May 7, 2003
Wallops Flight Facility, Wallops Island, VA
(Phone:  757/824-1579)
Keith.A.Koehler.1{at}gsfc.nasa.gov

RELEASE NO: 03 - 53

MAPPING THE GREENLAND ICE SHEETS

The ice sheet covering Greenland is expansive. Beyond the northern 
reaches of the Atlantic Ocean, Greenland is the largest island in the 
world and has the second largest mass of frozen fresh water on Earth. 
The ice and snow, covering 85 percent of the island, may provide 
important clues on global climate change.

Because of the importance of this ice sheet to Earth, NASA has been 
conducting aerial surveys of the island since 1992 using an aircraft 
carrying lasers and radars.  In May 2003 crews will return once again 
to Greenland to take a "snapshot" of large areas of the glaciers, 
which have shown some dramatic changes in recent years.

"The measurements obtained during the aircraft flights will help 
scientists better understand glacial changes caused by global climate 
change," said Bill Krabill, the lead NASA investigator for the 
mapping missions.

Some computer models show that increased global temperatures will 
partially melt polar ice sheets, such as those in Greenland, and 
raise sea level. Others show that rising temperatures will result in 
increased snowfall and expand the size of the ice sheets.

"Knowledge of any change in these glaciers may indicate trends in 
world climate and provide an indirect measure of sea-level changes," 
Krabill said.

Measurements by NASA and universities over the past 11 years have 
shown the glaciers shrinking along the southeast coast of Greenland. 
Scientists have surmised that melting ice flows down to the rock 
below the glaciers and acts like a lubricant between the ice and 
rock.  Thus, it becomes easier for the glacial ice to flow into the 
ocean. However, at the same time there has been an increase in the 
size of the ice sheet in the central portion of the island.

Krabill said, "We have to remember that these measurements only cover 
an 11-year life span of an island and ice cover that is many 
thousands of years old.  We really don't know if this is a normal 
cycle of events for these ice sheets or if this is a true sign of 
permanent change for the island, and thus sea-levels."

It has been estimated that a 10-inch (25-centimeter) decrease in the 
average height of the central Greenland ice sheet would result in a 
0.04-inch (1 millimeter) increase in the sea level of the world's 
oceans.

Scientists are scheduled to depart for Greenland on a NASA P-3B 
aircraft from the NASA Goddard Space Flight Center's Wallops Flight 
Facility, Wallops Island Va., on May 7.  During the next four weeks, 
through early June, the scientists will survey the Greenland ice 
sheet in the southern and northern parts of the island.

"You can take ice measurements from the ground, however, because the 
area you sample is small, you don't get an accurate look at the big 
picture of what's happening with the ice sheets," Krabill said.  "The 
aircraft allows us to cover much larger areas, and thus, obtain a 
more accurate picture of the ice sheets."

Advances in technology are what make it possible to develop maps of 
the ice sheets with very high accuracy, Krabill said.  Using Global 
Positioning System (GPS) receivers, the aircraft is able to fly 
flight lines year after year and keep within feet of the original 
flight line. This allows the mapping instruments to take measurements 
over the same area each year.

Using three different instruments this year, the scientists will be 
able to get a clear picture of the thickness of the ice sheet and 
information on depths of snowfall within recent years.

NASA will fly two laser systems on the aircraft that provide the 
scientists with the height or elevation of the ice. The instrument 
sends a laser pulse to the surface of the ice, scanning an area about 
650 feet (200 meters) wide below the aircraft. The ice then reflects 
the laser pulse back to the aircraft.  Knowing the speed of the laser 
light and the position and altitude of the aircraft, scientists can 
then develop a map of the ice sheet elevations. The laser system can 
help researchers develop maps of the ice sheet surface to an accuracy 
within 4 inches (10 centimeters).

Researchers from the University of Kansas, Lawrence, will fly two 
radars. One is an ice penetrating radar that will give scientists a 
map of the bedrock below or the location of the bottom of the ice 
sheet. Combining the radar information with the laser data, 
researchers can then determine the thickness of the ice sheet.

The second Kansas radar is a newly developed snow accumulation radar. 
This radar will measure the top 60 feet (20 meters) of the snow pack. 
This will help researchers in trying to measure the annual snowfall.

The data from this year's flights will be added to the information 
gathered from previous missions, providing researchers valuable 
information in further understanding the effects of global climate 
change on the world's ice systems.

More information on the NASA laser system, including uses for mapping 
other terrains, can be found at:
http://aol.wff.nasa.gov/aoltm.html

-end-

*****************************
Mark S. Hess
Chief, Office of Public Affairs
NASA/GSFC, Code 130
*************

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