It doesn’t get said nearly enough: We’re living in a golden age of topography. The days of guys tromping through the woods pounding geological survey points into the ground are gone, as is the 30 year lag in between new maps. The most futuristic-sounding technology possible—lasers from space—are going to map not only things that change at the pace of rocks, but also at a glacial pace. NASA has adapted LiDAR to map the Arctic ice.
“Light detection and imaging,” or LiDAR, has been used to map rainforest floors that remain unreached on foot, as well as the Long Island coastline. The maps it creates are three-dimensional with unprecedented detail. "Historically we've measured accuracy in meters. With LiDAR, we measure accuracy in centimeters," Larry Sugarbaker, a senior advisor to the Us Geological Survey, told The Atlantic’s Henry Grabar in September 2013.
In April 2012, NASA began testing LiDAR over Greenland in high-altitude airplanes. It fired pulses of green laser light down at the Earth and timed how long it took individual photons to bounce back, as a test of NASA’s new “Multiple Altimeter Beam Experimental LiDAR,” or MABEL tech. It can measure changes in the elevation of the Earth’s surface down to “to as little as the width of a pencil,” according to NASA.
Even for LiDAR this is exciting and uncharted territory. "Using the individual photons to measure surface elevation is a really new thing," said Ron Kwok, a senior research scientist at NASA's Jet Propulsion Laboratory said in a statement.
MABEL can distinguish the different patterns of photons as they bounce off of ice sheets that are on land or sea ice on water. "We wanted to get a wide variety of target types, so that the science team would have a lot of data to develop algorithms,” said Bill Cook, MABEL's lead scientist at the Goddard Space Flight Center, hence the flight over Greenland, which has a huge ice sheet, glaciers and sea ice in spades.
The laser is also split into six beams—three pairs that measure the slope of the land, which reduces the need for multiple passes.
This is all in preparation for the launch of the ICESat-2 satellite, slated for launch in 2017. The satellite will monitor ice sheet elevation change, sea ice freeboard, and vegetation canopy height over a 15 year period, creating datasets that will be used for long-term trend analysis. It will mostly be focused on Antarctica and the Arctic ice to begin with.
Counting photons allows scientists to calculate the height difference between sea ice and ice sheets, which is important for determining the ice’s thickness, crucial for measuring changes throughout the seasons as well as over years.
Before getting launched, MABEL will head back to Greenland in May. "We want to see what the effects of the melt is," Cook said. "How do glaciers look if they're warmer, rather than colder?"
I suspect slightly smaller, but this hypothesis can be confirmed or disproved soon enough, I suppose—to within the width of a pencil.