Month: March 2025

ICESat-2’s Laser Fires 2 Trillionth Shot, Spots Clouds

Happy 2,000,000,000,000th, ICESat-2! NASA’s Earth-observing laser in orbit passed a milestone on March 9 at 12:51 p.m. EDT — 16:51:00.268 UTC, to be precise — as its laser instrument fired for the 2 trillionth time and measured clouds off the coast of East Antarctica.

A data visualization with a bright blue background and dots, representing height measurements taken by ICESat-2. A vertical green line marks the satellite's 2 trillionth laser pulse. An inset map of Antarctica shows a green line from the interior of the continent, through a spot labeled Vanderford Glacier, and out into the southern ocean, locating data shown on the larger plot.
ICESat-2’s height-measuring laser instrument, ATLAS, fired its 2 trillionth shot on March 9, detecting clouds off the coast of East Antarctica. This data plot of surface heights marks that milestone with a vertical green line. In the few minutes before and after the shot, ICESat-2 measured the surface of the ice sheet and high clouds over the coast (in the left of the image), followed by clouds and a couple breaks where the ocean surface is detected. (Credit: NASA/A. Martino)

ICESat-2’s instrument, the Advanced Topographic Laser Altimeter System (ATLAS), uses rapid pulses of green laser light and an incredibly precise clock system to track the height of Earth’s surface from space. Its first measurements from orbit profiled the Antarctic ice sheet in September 2018.

Since then, it’s fired 10,000 times a second to provide height profiles of the planet’s changing glaciers, sea ice, water reservoirs, forests and more — even detecting the coastal seafloor in places.

The laser is in excellent shape, even after six years and a couple trillion shots, said Anthony Martino, ATLAS instrument scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. At this rate, it could last well into the 2030s, he said — and there’s a second laser aboard that the mission could switch to, if needed.

On a dark background, six rows of dots arranged in pairs go from the top left of the image toward the bottom right in a bumpy, uneven slope - data measurements of a glacier surface.
ICESat-2’s six beams measured height profiles of Vanderford Glacier less than two minutes before the 2 trillionth shot, capturing the glacier’s topography and the surrounding ice. (Credit: NASA/ A. Martino)

While the primary mission of ICESat-2 is to measure ice, ATLAS operates around the clock and the 2 trillionth shot captured a common sight: clouds. About 79 seconds earlier, it passed over the clear skies of the Antarctic ice sheet as it flows down Vanderford Glacier and into the Southern Ocean.

Vanderford Glacier is East Antarctica’s fastest retreating glacier, as warmer ocean water seeps in to melt it from below, according to a recent study. And it’s a prime example of what scientists can use ICESat-2 data for, said Denis Felikson, ICESat-2 deputy project scientist at NASA Goddard.

to the left, a map of a section of East Antarctica with ice height gains, in blue, and losses, in red, from ICESat-2 data between 2019 and 2024. Vanderford Glacier is labelled and red. To the right, a line graph showing the drop, then slight rebound, then drop in elevation of a site on Vanderford.
An ICESat-2 data visualization shows the gain (blue) and loss (red) of ice in Vanderford Glacier (black circle) and the nearby regions of East Antarctica between 2019 and 2024. Taking data from a single site within that black circle, scientists can also get a continuous picture of the ice throughout the years. (Credit: D. Felikson/NASA)

Tracking a specific site on Vanderford throughout ICESat-2’s record, for example, shows how the ice surface dropped about six feet between 2019 and 2022, rose a few feet the next year, but then dropped back down in 2024. Zoom out, and researchers can track elevation across the glacier and its surroundings.

“With data from 2 trillion laser shots, and more to come, we have this consistent global record of all of Earth’s ice from space, at glacier scales but also in really fine detail,” Felikson said. “Both of these scales are critical for us to understand how Earth is changing over time.”

Against a black background, a line of bright blue dots go in a wavy horizontal line. These are height measurements of ocean waves from ICESat-2.
Through a break in the clouds a few seconds after the 2 trillionth shot, ICESat-2 captured waves of the Southern Ocean. (Credit: A. Martino/NASA)

By Kate Ramsayer, NASA’s Goddard Space Flight Center