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Ralph Dubayah: So we often talk about the biomass of the forest.

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All that is how much do the trees weigh.

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If you know their biomass, how much they weigh,

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half of the biomass of the tree is carbon

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Well, my name is Ralph Dubayah.

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I'm the principal investigator of the GEDI mission

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and I'm a professor of geographical sciences at the University of Maryland.

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It's really critical that we understand

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what the current carbon content of forests is today.

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We need a good global map of where the carbon is.

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The reason we need that is because whenever we cut down trees,

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we're going to release carbon into the atmosphere

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and we don't know how much carbon we are releasing.

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GEDI will tell us how tall the trees are

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and by knowing how tall they are we will know how much they weigh;

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by knowing how much they weigh, we will know how much carbon

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is being lost into the atmosphere.

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Bryan Blair: So GEDI weighs about a thousand pounds

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and looks about like a refrigerator.

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So it has a telescope about 80 centimeters in diameter.

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It has three laser ports, and shoots out four laser beams

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that are then dithered, really quickly, in between shots.

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So it makes one laser look like two.

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So I'm the instrument scientist for GEDI,

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and that's sort of the translator between engineering and science.

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So Ralph and I, we've been working on GEDI for over 20 years,

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and trying to get the technology ready and the science ready,

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so we can fly a mission like this.

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It's been great to get to this point.

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OK, so GEDI is a laser altimeter,

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so it's an active optical instrument.

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We have lasers that emit pulses of light.

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They travel down to the Earth, they get reflected from the Earth,

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and then we receive the reflection.

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So we time how long it takes to get there,

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which allows us to measure the range to the surface.

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When the pulse of light hits the surface

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it gets distorted and stretched out by any structure that is there.

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Ralph: It looks almost like an echocardiogram.

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It's a distorted Gaussian waveform, technically speaking.

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And where the amplitude of that waveform is bigger

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is where there's more canopy stuff.

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There's more leaves and branches at a particular height.

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And where the amplitude is smaller, there's less canopy material.

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Bryan:  The overall goal of GEDI is to systematically and consistently

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sample the vertical structure of the world's forests,

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so we can estimate from that structure, the carbon content of the forest.

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Ralph: Really, one of the coolest things about GEDI

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is that we're going to get upwards of 10 billion

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-- ten billion -- estimates of how tall trees are.

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It's highly likely that trees on your block

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are going to be measured by GEDI and you'll be able to see how tall they are.

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We simply do not know how tall trees are globally.

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So this is really, really exciting and really cool.

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You can take your kids down your block and say, hey, GEDI measured that tree.

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