http://www.digitaljournal.com/tech-and-science/technology/nasa-launching-advanced-laser-to-measure-earth-s-changing-ice/article/530304

NASA launching advanced laser to measure Earth's changing ice

Posted Aug 24, 2018 by Karen Graham
Next month, NASA will launch into space the most advanced laser instrument of its kind, beginning a mission to measure – in unprecedented detail – changes in the heights of Earth's polar ice.
An artist s rendition of the ICESat-2 satellite
An artist's rendition of the ICESat-2 satellite
NASA/Goddard
Called the Ice, Cloud and Land Elevation Satellite-2 (ICESat-2), the mission is currently scheduled to launch in mid-September. ICESat-2 will measure elevation changes on Earth, one laser pulse at a time,
The mission will measure the average annual elevation change of land ice covering Greenland and Antarctica to within the width of a pencil, capturing an unbelievable 60,000 measurements every second. To put this more in perspective, the decadal mission will measure the changing thickness of individual patches of ice from season to season and year to year.
"The areas that we're talking about are vast — think the size of the continental U.S. or larger — and the changes that are occurring over them can be very small," Tom Wagner, a NASA scientist studying the world's ice, said during a news conference on August 22, reports Space.com. "They benefit from an instrument that can make repeat measurements in a very precise way over a large area, and that's why satellites are an ideal way to study them."
Artist s impression of ICESat in orbit
This is the first ICESat mission satellite.
Artist's impression of ICESat in orbit This is the first ICESat mission satellite.
NASA/Ball Aerospace
ICESat-2 is the third NASA ice project
The original ICESat mission was launched January 13, 2003, on a Delta II rocket from Vandenberg Air Force Base in California. It was designed to provide elevation data needed to determine ice sheet mass balance as well as cloud property information, especially for stratospheric clouds common over polar areas.
But ICESat also provided topography and vegetation data around the globe and was very helpful in assessing tree density in forests around the world. All this was accomplished with a single Geoscience Laser Altimeter System (GLAS), a space-based LIDAR. When the ICESat mission ended in 2009, ICESat-2 wasn't quite ready, so NASA developed a stop-gap program.
NASA was ready with a new program called Operation IceBridge that began in 2009 with the primary goal being to monitor changes in the polar ice in both the Arctic and Antarctic regions. The yearly surveys using a fixed-wing aircraft were meant to provide continuity from the end of the ICESat mission until the launch of the ICESat-2.
Glacier Canyons in NW Greenland.
IceBridge Mission  May  2017.
Glacier Canyons in NW Greenland. IceBridge Mission, May, 2017.
NASA
And for the past eight years, NASA has provided some astounding and unprecedented three-dimensional views of the polar regions, providing scientists with valuable data on how polar ice is changing in a warming world and allowing the public to see first-hand some truly incredible landscapes.
ICESat-2 mission in September
Here's an interesting bit of trivia - The reason NASA is now using lasers to get three-dimensional images of the ice is because space-based cameras only give a two0-dimensional view. And the lasers have brought some disturbing news.
"What ICESat found is that the sea ice is actually thinning," Wagner said. "We've probably lost over two-thirds of the ice that used to be there back in the '80s."
ICESat-2 will carry a single instrument – the Advanced Topographic Laser Altimeter System, or ATLAS, which times the travel of laser pulses to measure the elevation of Earth’s surface. New technologies will allow ATLAS to collect a more detailed, precise picture of heights of Earth’s surfaces
ATLAS will actually carry two lasers, with one as a backup. The laser light is at 532 nanometers, a bright green on the visible spectrum. And it is fast-firing – it sends 10,000 pulses per second, as compared to the laser on the first ICESat, which sent 40 pulses per second.
The pulses of light travel through a series of lenses and mirrors before beaming to the ground. This pathway along the optical bench serves to start the stopwatch on the timing mechanism, check the laser's wavelength, set the size of the ground footprint, ensure that the laser and the telescope are perfectly aligned, and split the laser into six beams.
"ATLAS essentially acts like a stopwatch," Donya Douglas-Bradshaw, instrument manager for the laser, said during the news conference. "The ATLAS laser fires 10,000 pulses a second, with a trillion photons in each shot. Each time the laser fires, it starts the stopwatch." Scientists can then convert that time into a distance, calculating the height of the surface at that specific location
The ICESat-2 launch from Vandenberg Air Force Base in California is expected to take place on Sept. 15, during a window that opens at 5:46 a.m. local time (8:46 a.m. EDT, 1246 GMT) and closes at 8:20 a.m. local time (11:20 a.m. EDT, 1520 GMT). ICESat-2's launch will be the last voyage of United Launch Alliance's Delta II rocket, which has seen more than 150 launches over its nearly 30-year career.