On September 15, NASA’s ICESat-2 satellite left Earth on the last Delta II rocket. Happily, the satellite is providing a successful send-off to the Delta II, as it has started its important mission without incident. On Wednesday, NASA showed off the first data beamed down: measurements of Antarctica’s glacial ice.

Like its predecessor, ICESat-2 is a laser altimeter that can very precisely map surface elevations. These satellites were designed with changing surface elevations in mind—chiefly the declining sea ice and ice sheets of the polar regions. The original ICESat had a seven-year run that ended in 2010. Without ICESat-2 ready to go, NASA turned to similar instruments onboard planes to collect what data they could in the meantime—an intensive project titled Operation IceBridge.

Compared to some other Earth-observing satellites, the principle at work here is pretty simple, though the engineering that makes it work is approximately miraculous. The satellite shines a laser pulse at the Earth and measures how long it takes to reflect back. Do the math (speed of light and all that) and you have the distance between the satellite and the ground. With precise knowledge of the satellite’s position, you can map surface elevation around the globe in great detail.

Although ICESat-2 actually uses the same wavelength of light as a green laser pointer, you don’t have to worry about being blinded by looking upward at an unlucky moment. It’s not an astoundingly bright laser that makes the satellite work but an incredibly sensitive telescope. While trillions of photons of laser light are sent down in each pulse, only a dozen or so make it back to the detector on the satellite—a fact NASA chose to illustrate with what is perhaps an excessively cute video with cartoon photons.

The delay between ICESat’s demise and the launch of ICESat-2 at least came with an upgrade to the instrument. While the first satellite had a resolution of about 100 meters per “pixel,” ICESat-2 knocks that down to just 0.7 meters, sending 10,000 pulses of laser light each second. It should also be slightly more sensitive, detecting surface elevation changes smaller than one centimeter per year.

#ICESat-2’s laser is firing, and we have our first height measurements of the Antarctic ice sheet! 🛰️🇦🇶 https://t.co/w9LmFYlOB7 pic.twitter.com/v2967GlMvD — NASA Ice (@NASA_ICE) October 3, 2018

ICESat-2 orbits from pole to pole, repeating measurements of each location on the Earth every 91 days. These measurements can track the shrinking (or growth) of glacial ice, as well as the thickness of sea ice. The data can also show interesting things over non-frozen areas of the planet, though. The height of forest canopies can be calculated as some photons bounce off trees and others sneak back up from the forest floor. Land surface movement due to fault shifting during an earthquake can also be detected, as can changes in reservoir or lake levels.

With everything looking good so far, NASA says the ICESat-2 team will spend a couple weeks testing and optimizing the instrument before flipping the switch to official data collection. Although the European Space Agency has thankfully had the similar (but radar-based) CryoSat-2 in orbit since 2010, you can bet glaciologists and other scientists are eager to see this new satellite’s data start streaming in, eight years after the first ICESat went dark.