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Markus: From satellite data,

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we have a very good handle of how our Earth looks like. We can see oceans,

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we can see the sea ice, we can see our forests, but it's much, much

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harder to measure how high things are on a global scale. Almost impossible.

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Neumann: ICESat-2 adds the third dimension, the elevation. Repeating measurements

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from ICESat-2 will allow us to measure changes in the ice sheets or in the

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ocean or in land.
Markus: ICESat-2 is designed to measure

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the changes that are going on in the cryosphere, in the polar regions.

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Neumann: All the change is at the edges. Those are the steeply sloping parts of the glacier

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interact with the ocean, and that's where all the action is, that's where all the mass is being lost.

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Markus: In order to estimate the mass changes, we need to know the height

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of things. The mission, ICESat-2,

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carries a single instrument. It's called ATLAS, the Advanced Topographic

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Laser Altimeter System.
Neumann: ATLAS sends out

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small pulses of laser light 10,000 times a second, and by

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measuring precisely how long it takes that light to go from the spacecraft

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down to the Earth and back up to the spacecraft allows us to figure out

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what the height of the surface is beneath ICESat-2.

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Markus: We need to measure the time of flight of a single photon, or a single laser pulse,

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with the precision of a billionth of a second.
Neumann: NASA engineers had to come up with

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entirely new ways of measuring time very precisely.

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Markus: A billionth of a second translates to an elevation-change precision of

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just a few centimeters. Climate change is amplified in

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the polar regions. ICESat-2 is designed to measure those

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areas and will help us to understand what's going on with our planet.

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