NASA would like you to take a picture of a tree, please. The space agency’s ICESat-2 satellite estimates the height of trees from space, and NASA has created a new tool for citizen scientists that can help check those measurements from the ground. All it takes is a smartphone, the app, an optional tape measure, and a tree. Launched in September 2018, the ICESat-2 satellite carries an instrument called ATLAS that shoots 60,000 pulses of light at the Earth’s surface every second it orbits the planet. By measuring the satellite’s position, the angle, and how long it takes for those laser beams to bounce back from the surface, scientists can measure the elevation of sea ice, land ice, the ocean, inland water, and trees. Knowing how tall trees are can help researchers estimate the health of the world’s forests and the amount of carbon dioxide they can soak up. The only question that remains for NASA scientists is how good those measurements from space actually are. That’s where you, the citizen scientist, come in — to help verify them. To play your part, all you need to do is download the NASA GLOBE Observer app and choose from a number of tools that allow you to record your observations in the name of science.