The green light streaming across the cloudy sky was something Daichi Fujii had never seen before. The museum curator’s motion cameras were placed near Japan’s Mount Fuji to capture the meteors, allowing him to calculate their position, brightness and orbit. But the bright green lines that appeared in the video taken on September 16, 2022, were a mystery.
Then Fujii looked closer. The beams were synchronized with a small green dot that was briefly visible between the clouds. He guessed it was a satellite, so he examined the orbital data and found a match. NASA’s Ice, Cloud and Land Elevation Satellite 2, or ICESat-2, flew overhead that night. Fujii posted his findings on social media, which eventually got the attention of the NASA team.
This is the first time the ICESat-2 team has seen footage of the satellite’s green laser beams streaming from Earth orbit, said Tony Martino, ICESat-2 instrument scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
“ICESat-2 appeared to be almost directly overhead, with the beam striking the low clouds at an angle,” Martino said. “To see a laser, you have to be in the right place, at the right time, and you have to have the right conditions.”
Green light streaming across the cloudy sky Daichi Fujii
ICESat-2 was launched in September 2018 with the mission of using laser light to measure the height of Earth’s ice, water and land surfaces from space. A laser device called a lidar fires 10,000 times per second, sending six beams of light down to Earth. It precisely measures how long individual photons take to bounce off the surface and return to the satellite.
Computer programs use these measurements to calculate ice loss from Greenland and Antarctica, observe how much of the polar oceans are frozen, determine the heights of freshwater reservoirs, map shallow coastal areas, and more.
Laser light fired from hundreds of miles in space is not harmful. It’s actually hard to find out. If someone stood directly below the satellite and looked up, the laser would have the power of a camera flash at a distance of more than 100 yards, Martino said.
People tried to take pictures of the satellite as it flew by, and in several cases they managed to capture photos once from southern Chile and once from Oklahoma.
The beam is even more difficult to capture, he noted, because cameras and eyes need the laser light to bounce off something to see the beam from the side. That’s where the atmospheric conditions come into play.
However, on the night ICESat-2 passed over Fuji City, there were enough clouds to scatter the laser light making it visible to the cameras but not enough to block the light completely. There were actually two thin layers of clouds over Japan that night information that Martino discovered by analyzing ICESat-2 data, which shows both the clouds and the ground beneath them.
Thanks to the exact position of the satellite in space, the point of impact of the beam, the coordinates where the Fujii cameras were set, and the addition of cloud cover, Martino was able to definitively confirm that the streaks of light came from Laser ICESat-2.
