[music] Narrator: NASA’s airborne surveys are
are giving scientists astonishingly accurate views of how
Greenland’s glaciers are changing.
Laser altimeters map the very details of glacier surfaces
and flights spanning two decades reveal the dramatic changes
that have taken place.
[atmospheric music]
On Greenland’s rugged eastern coast, spilling into
a mountainous fjord, lies the four-mile-wide
Helheim Glacier, named for the Viking world of the dead.
It’s had a wild ride over the last 20 years,
first rapidly retreating and thinning, then partially recovering
its former extent. NASA science
missions have flown the glacier’s center line year after year,
collecting a wealth of valuable data.
It all begins
with a single beam of light.
Firing several thousand pulses per second, laser instruments on board
research aircraft measure the height of the surface below.
The lasers spin in a
250 meter circle. providing a swath of data that can be
turned into a topographic map of the ice.
Here we’ve shown higher elevations
in red and orange, and lower elevations in green and blue,
all the way down to the glacier’s calving front –
where Helheim’s mighty icebergs break off into the sea.
But one snapshot
only tells part of the story. Here’s a 1998
swath compared with 2013.
We’ve changed the color scale to highlight the local
differences in elevation.
We’re now moving below the surface of the ice as it was in 1998,
and over the mélange of icebergs and ocean that were present in the same spot
in 2013. The calving front of the glacier
has retreated significantly, by two and half miles.
The glacier has thinned as well. We couldn't have flown at this elevation
15 years ago. This all would have been ice.
NASA’s Operation IceBridge, which has been measuring Greenland
since 2009, has added to the laser data from previous missions
with new instruments like ice penetrating radar,
a magnetometer, and a gravimeter. It’s also used a
high-resolution camera system, taking overlapping images of the ice
throughout its eight-hour flights.
These images can be pieced together
into a mosaic, and since they overlap, provide us with a
stereoscopic view of the ice, and an elevation model of their own.
Here is that model overlaid onto the laser data,
as we approach Helheim’s 70 meter high calving front.
As we get
close to the glacier’s terminus, large cracks in the ice, called crevasses
get longer and deeper, a sign new icebergs
will soon join their comrades on their way out to sea.
Until the launch of a
new NASA satellite, ICESat-2, Operation IceBridge
will return to Greenland every spring to continue measurements
of this large and ever-changing glacier.
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