On September 15, NASA will launch a laser 310 miles above the Earth to scan our planet’s ice sheets like never before, recording changes in the elevation of these frozen landscapes down to the width of a pencil.

The laser, which lives aboard NASA’s Ice, Cloud and land Elevation Satellite-2 (ICESat-2), will shower the Earth with subatomic particles of green light called photons—300 trillion per laser pulse, to be exact. The satellite will survey Earth from pole to pole, flying 1,387 unique tracks every 91 days for as long as its fuel supply and hardware systems hold. By the mission’s end, scientists are expecting a slew of new data that will help reveal where ice is retreating fastest as global temperatures rise and what that means for our future.

ICESat-2 is, basically, Christmas-come-early for climate and ice scientists. (Or a few years late depending on how you look at it, NASA had originally hoped for a launch in 2016 before technical difficulties set the mission back.) The fact that it’s now launching under the auspices of a president who last year suggested global warming might not be real because of a snowstorm hasn’t tamped down spirits at NASA, an agency that has, so far, proven fairly impervious to the political headwinds of the Trump administration.

If there are any jitters at this point, they’re over the success of the launch. “My own place on the spectrum of excited to terrified fluctuates daily,” Tom Neumann, NASA’s deputy project scientist with ICESat-2, told Earther.

As its name suggests, ICESat-2 is a follow-on to an original ICESat mission—a satellite that launched in 2003 and collected data until 2009.

Both missions are all about measuring the elevation of icy surfaces. To do so both rely on laser altimetry—shooting pulses of light at the ground, and determining the time it takes for some of that light to return to the satellite. Combining that travel time with the satellite’s precise location and the laser’s pointing angle, the distance from satellite to ground can be calculated and used to work out elevation.

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But that’s where the similarities between ICESat’s Geoscience Laser Altimeter System—the very first laser altimeter launched into space on a satellite—and ICESat-2's Advanced Topographic Laser Altimeter System (ATLAS) end. The latter amounts to a major upgrade when it comes to studying icy surfaces.

The original ICESat fired a single beam of light 40 times a second, allowing it to measure elevation about every 560 feet (170 meters) along Earth’s surface. ATLAS fires 10,000 pulses a second, and the laser light is split into three pairs of beams as it exits the instrument. Pairs of beams are spaced 1.9 miles (3 kilometers) apart on the ground.

The faster firing means ICESat-2 will take elevation measurements every 28 inches—a dramatic increase in resolution. What’s more, having three spaced-out laser pairs instead of a single beam will allow ICESat-2 to measure the slope of its track as the satellite flies overhead.

Finally, while the original ICESat mission only wound up operating about two months a year due to some laser life time issues, ICESat-2 will take measurements year-round. “There’s just going be more data than we necessarily know what to do with,” Brooke Medley, a glaciologist at NASA’s Goddard Spaceflight Center, told Earther.

Combining all that data with other information collected remotely via satellites or aircraft or in the field, scientists hope to improve their estimates of everything from the thinning of ice shelves holding back West Antarctica’s most imperiled glaciers to subtle changes in East Antarctica’s icy plains that could have a major impact on future sea level rise.

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ICESat-2 is also the first instrument optimized to measure not just the aerial extent but the thickness of sea ice, which can tells us about the ice’s age and health. The timing seems fortuitous: Just this past year, scientists witnessed open water forming not once, but twice, north of Greenland in a region where the oldest and thickest Arctic sea ice was thought to reside.

Beyond the big picture stuff, ICESat-2's data will inform any number of more focused research projects. Helen Fricker, a professor of glaciology at the Scripps Institution of Oceanography, is looking forward to checking in on more than 100 subglacial lakes—lakes that form beneath ice sheets—discovered by the original ICESat mission. We’re only just beginning to understand these lakes, which can fill or drain over the course of several seasons, potentially impacting the dynamics of the ice they’re buried beneath.

“We’re very excited because as soon as we get data on these lakes, we’ll know if they’ve drained or filled since [the original] ICESat ended,” Fricker told Earther, noting that with ICESat-2's wider field of view, we should also be able to detect new subglacial lakes.

A meltwater pond photographed on an Alaskan glacier in 2014.
Photo: NASA

Indrani Das, an assistant research professor of glaciology at Columbia University’s Lamont-Doherty Earth Observatory, is excited about a different sort of lake. She’s hoping to take advantage of ICESat-2's green-colored laser light to measure the depth of meltwater ponds that form on the surface of ice sheets during the summer months. The original ICESat mission, which beamed infrared light, wasn’t super useful for this.

“Infrared is absorbed by water, so it doesn’t penetrate [the ponds],” Das told Earther. “But green can. That’s a unique thing I’m really looking forward to.”

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Then there are applications that have nothing to do with ice at all. Some researchers, for instance, are interested in what this satellite can tell us about Earth’s remote high-latitude forests.

Laura Duncanson, an assistant research professor at the University of Maryland College Park and NASA Goddard, told Earther the original ICESat mission was useful for estimating things like forest height, canopy cover, and biomass, information that’s used to make global forest carbon maps that inform climate change models. While ATLAS may have trouble penetrating densely-canopied tropical forests, it should help scientists estimate forest structure and biomass in the more open boreal forests covering vast swaths of North America and Eurasia. Another laser altimeter mission launching to the International Space Station this fall—the Global Ecosystems Dynamics Investigation, or GEDI—will be optimized for forest structure studies, but it won’t be flying north or south of about 52 degrees latitude.

“The synergies between ICESat 2 and GEDI will be particularly exciting,” Duncanson told Earther. “Everywhere GEDI won’t cover, ICESat 2 will.”

ICESat-2's road to readiness has been long and at times rocky. As a report published last year by NASA’s Office of the Inspector General detailed, managers underestimated the complexity of building ATLAS when the mission entered development in 2012. As a result, NASA “significantly understated the mission’s cost and schedule,” ultimately drawing funds from other Earth science projects to finish it, per the report.

Donya Douglas-Bradshaw, a mechanical engineer at NASA who took over as project manager for ATLAS in 2014, says unexpected roadblocks are par for the course when developing an instrument like this. “Anytime you’re building something new you’re gonna have challenges,” she told Earther.

In her view, though, the challenges are worth it for what missions like this are ultimately able to offer the scientific community.

“To hear the scientists talk about what they’re gonna do and what they’re gonna learn, and to realize you had a part in orchestrating this huge instrument that took a huge team of people and to see it work, it’s just amazing,” Douglas-Bradshaw said. “I’m just amazed at what we’re able to accomplish.”