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The shape of what we

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build, live, work, study, operate--on
whether it be on the Earth,

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the Moon, Mars,
wherever we're going--

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--matters.

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Knowing that at a scale where
we can understand what's going to happen,

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what has happened and predict
what could happen, is really important.

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Laser altimetry, as developed here
at Goddard, went from an idea

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to try to capture that

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into something we can actually do.

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[music]

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In 2018

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NASA launched two next-gen lidar missions

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specifically to look closely at our changing planet.

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But if over three decades of lidar
missions has taught us anything,

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it's that laser altimetry at Goddard
is an evolution of technology,

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propelled by scientific curiosity
in the face of almost certain setbacks.

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Take the story of the tree-measuring lidar:

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the Global Ecosystem Dynamics Investigation,

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or GEDI.

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GEDI had its genesis really

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in all the innovative work
that had been done with lidar at Goddard.

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Some of those innovators, this was Jack
Bufton and Bryan Blair at Goddard.

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Bryan had an instrument called SLICER that was flying around,

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taking these cool lidar transects.

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And then they put an instrument
up in space, the Shuttle Laser Altimeter.

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And I saw some of that data and I thought,

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Wow, this is really cool.

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We've never been able to look at canopies in three dimensions like this.

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There's certainly got to be some applications to this.

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The Shuttle Laser Altimeter was the first real test for lidar

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and provided the momentum for MOLA
to take on Mars.

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But it also gave us a glimpse at what
lidar could measure on our own planet.

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And so the push for the Vegetation Canopy Lidar, or VCL, began.

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It was a really innovative mission.

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We were trying to do something

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that hadn't been done before,

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but we were optimizing it for vegetation.

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Vegetation is very different
than if you're looking at ice,

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or if you're looking at Mars,
or if you're looking at the Moon,

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because you have to have enough
laser power to get through the canopy

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and get a strong return underneath the ground.

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The VCL team could build lasers strong enough,

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but they couldn't get them to last very long.

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And that proved too risky
for very cautious NASA in the nineties.

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After that happened,
we focused on the airborne lidar program,

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and this is again with Bryan Blair

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using that really innovative instrument

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he had called LVIS,

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the Land, Vegetation and Ice Sensor, I believe it's called.

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If you really want to get down
to really high resolution

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and looking at the sort of landscape-scales

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changes over the Earth, 

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you need a swath mapping system.

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So,

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sort of in the mid nineties
we started working on LVIS, and you know,

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we really worked on that in large part
because people said it couldn't be done,

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and you know, it's really
kind of drove us to

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to see how much we
could get out of that system.

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[airplane engine sound] Airborne

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missions were successful
at keeping that momentum going,

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especially in the long periods
between satellite launches.

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Sort of a core of us kept going year after year,

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going from one instrument opportunity to another,

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and sort of making opportunities
if we didn't have any.

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The thread that kept us all going
was the airborne system.

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Airborne lidar really plays
a role helping us

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understand how things work in real world settings.

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Yeah that's definitely, definitely
the best way to go

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was to build the hardware,
get some data over real terrain and

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and actually, you know,

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show that it meets the requirements,
that you can scale it to the space.

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But along the way also as we were flying,
as we were collecting those data sets,

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we were releasing those publicly
and letting people experiment with them

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and get comfortable with them.

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Dubayah, Blair and others
leveraged the success of LVIS to propose

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a new satellite mission,

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DESDynI, a combined radar and lidar mission

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that could see through clouds down to tree canopies.

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However, NASA's budget cuts sidelined a couple of Earth science missions,

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and DESDynI was grounded indefinitely.

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And that was a devastating blow
because we now been trying from 1995

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and now it's 2010,
we've been trying to get a lidar

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that was meant just for vegetation structure into space,

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using the best people in the world
who were at NASA Goddard to do this.

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And at that point, I've been doing this 15 years.

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Maybe I'll just quit.

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[music hit]

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But of course we really didn't quit.

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So we said, Well,
let's look for another opportunity.

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That opportunity was on board
the International Space Station with

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the GEDI instrument.

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GEDI wasn't just another successful lidar.

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It was the end of a very long road,

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 hard fought by scientists and engineers,

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dedicated to pushing the limits of what lidar could do.

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We've been really pretty happy
about the success of GEDI thus far.

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GEDI again is the first lidar
that's been in space

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that was optimized to
to measure vegetation structure.

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And it has--it's created
an enormous amount of data.

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We've conservatively done
about ten billion estimates,

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about getting those tree heights
and getting that canopy structure.

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But ultimately, we really wanted
to get at the carbon content.

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What role do forests
play in the carbon cycle?

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GEDI has been steadily gathering data,

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chipping away at the global question
of just how much carbon dioxide trees

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take out of the atmosphere,
a big piece of the climate puzzle.

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The current lidar missions
are all about building on the past.

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Things that we in fact
have only just begun

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to think about from pictures,
now we have the third dimension.

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ICESat will add the third dimension.

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ICESat-2 will add the third dimension, the elevation.

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Pushing the technology
to get at deeper science questions.

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And so came the next generation 
of ice-focused laser altimeters,

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aptly named ICESat-2.

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Its single instrument,
ATLAS, was designed to precisely measure

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small changes in the shrinking,
icy poles of Earth.

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To get down to that level of accuracy

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from space,

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everything had to be much better.

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It's this story of these incremental
improvements through time,

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and with each mission, you're leveraging
the lessons of the last mission.

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It wasn't a short process

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for ICESat-2, even though we knew a lot

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and had learned a lot over the last 20 or 30 years.

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Each mission, you know, has its own challenges.

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All of the easy missions are done, as they say.

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The first iteration of the

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instrument was going to be very similar to GLAS.

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As it turned out, the group that wanted
the more complicated instrument won.

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So then they came back and said,
okay, instead of digitizing,

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you know, 40 hertz or 50 hertz laser
or whatever, we're going to fire

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this beam to the ground.

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And then individually time tag

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each photon that comes back.

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There were so many requirements,

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there were so many constraints.

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We had constraints on the software capability.

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We had constraints on the storage space.

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We had constraints on the memory.

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By photon tagging--I mean they'd built
a detector system and detector electronics,

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they were just--it was like

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a firehose of data coming into us.

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ATLAS has six beams, and it records elevations

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for each of those six beams, 10,000 times
a second, as long as there is reasonably

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clear skies that the laser light
can go from the spacecraft to the ground

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and back again.

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The Earth is much more complicated to work with

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because of the clouds.

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The algorithm could easily be confused

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and start following, you know, the cloud surface.

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I was the lead for the receiver algorithms team.

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The responsibility of making this work
fell on my shoulders.

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I had sleepless nights.

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I have to tell you,

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thinking that I wasn't going to be able

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to make this work.

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In order to maximize the return from these data,

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a key component was determining
the location on Earth

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of the laser bounce point,

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a process called geolocation.

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So what we do and geolocation, we get the

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we get the position of the satellite

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really accurately.

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We get the pointing of the laser beam very accurately,

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and then we have the range from the altimeter,
and we add all those together

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to give us where
that bounce point came from.

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Without the geolocation, you have lots
and lots of error and you wouldn't be able

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to measure the change
in the height of the ice sheets.

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We overcame what I think was

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fairly insurmountable problems,

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but everybody took their own piece
of the puzzle and everybody worked it.

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[rocket launching]

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ICESat-2 launched in 2018 and months
later began gathering data

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that shed new light
on how fast the ice sheets are changing,

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how thick the sea ice cover
was in the Arctic,

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and even measured beneath the surface of the water,

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up to 30 meters, a kind of bonus science result

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for a team that worked tirelessly to push the limits

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of the ATLAS instrument.

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So you cannot just build just one lidar.

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You need a sustained team

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who's been building lidar for some time.