Firing laser pulses
With laser altimetry, laser instruments on board the research aircraft fire several thousand pulses of light every second. The results reveal the height of the surface below.
The lasers spin in a circle that's 820 feet (250 meters) across, which provides a swath of data that an be transformed into a topographic map of the ice, NASA said.
Here, higher elevations on the glacier are shown in red and orange, while lower elevations are in green and blue.
1998 calving event
The laser altimeters showed height measurements all the way down to the Helheim Glacier's calving front, where icebergs break off into the sea.
Icebergs break off
Here's a 1998 swath compared with one from 2013. In this image, the color scale is changed to show the local differences in elevation, according to NASA.
The 2013 swath from the laser altimeters reveals that the calving front retreated significantly since 1998, by 2.5 miles (4 kilometers), according to the NASA video.
NASA's Operation IceBridge mission has also used a high-resolution camera system to take overlapping images of the ice of Helheim Glacier throughout its 8-hour flights. These images can then be pieced together into a mosaic.
Because the images overlap, they can provide scientists with a stereoscopic view of the ice and even elevation measurements. The NASA scientists overlaid the elevation information from the images on top of the measurements from the laser altimetry.
Steep calving front
Helheim's calving front, which is 70 feet (21 meters) high, can be seen here.
Until the launch of a new NASA satellite called ICESat-2, the Operation IceBridge mission will return to Greenland every spring to continue monitoring the glacier, NASA said.