Markus: From satellite data, we have a very good handle of how our Earth looks like. We can see oceans, we can see the sea ice, we can see our forests, but it's much, much harder to measure how high things are on a global scale. Almost impossible.
Neumann: ICESat-2 adds the third dimension, the elevation. Repeating measurements from ICESat-2 will allow us to measure changes in the ice sheets or in the ocean or in land.
Markus: ICESat-2 is designed to measure the changes that are going on in the cryosphere, in the polar regions.
Neumann: All the change is at the edges. Those are the steeply sloping parts of the glacier interact with the ocean, and that's where all the action is, that's where all the mass is being lost.
Markus: In order to estimate the mass changes, we need to know the height of things. The mission, ICESat-2, carries a single instrument. It's called ATLAS, the Advanced Topographic Laser Altimeter System.
Neumann: ATLAS sends out small pulses of laser light 10,000 times a second, and by measuring precisely how long it takes that light to go from the spacecraft down to the Earth and back up to the spacecraft allows us to figure out what the height of the surface is beneath ICESat-2.
Markus: We need to measure the time of flight of a single photon, or a single laser pulse, with the precision of a billionth of a second.
Neumann: NASA engineers had to come up with entirely new ways of measuring time very precisely.
Markus: A billionth of a second translates to an elevation-change precision of just a few centimeters. Climate change is amplified in the polar regions. ICESat-2 is designed to measure those areas and will help us to understand what's going on with our planet.