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Doug Morton: The forests of Puerto Rico are always changing.

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Following Hurricane Maria, they've changed a lot.

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But by taking measurements on the ground,

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in the air, and from space,

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we're able to not only identify those changes,

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but also follow them through time

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as these landscapes recover the lush tropical forests

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they had before the storm.

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Narrator: NASA scientists were in Puerto Rico

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in early 2017, studying how forests grow and change.

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They returned in 2018 to assess the forest recovery

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after two hurricanes hit the island.

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Doug: In many ways, Hurricane Maria has reset

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patches of forest across the island.

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Canopy trees normally have a large and

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sometimes circular crown allowing them

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to spread their leaves, photosynthesize, and

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live in the top of the canopy.

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Hurricane Maria came through and

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ripped off many of those large branches,

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leaving individuals standing almost like an individual stem. 

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What that means is they'll have to regrow

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those leaves or give up that space in the canopy

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to their neighbors as they regrow beneath them.

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Narrator: The team returned to the specific plots

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they measured the previous year,

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hiking through the thick under brush that had grown

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since the hurricane opened up the canopy.

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A bit like this, Ian?

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Doug: When this large tree fell,

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it took out most of its neighbors

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and created a large gap in the forest where sunlight

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will now reach all the way down to the forest floor.

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That will allow new, young trees to grow back in its place. 

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In contrast, on this side of the plot,

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many of the large trees were stripped of their large branches

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but they are still standing and most of them will recover

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those leaves and grow back into the space they left behind.

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Narrator: But with forests covering half of the island,

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walking up to every tree was not practical.

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Bruce:   So, my name is Bruce Cook,

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I'm from NASA Goddard Space Flight Center. 

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I'm here today in Puerto Rico, assessing damage

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that was caused by both Hurricanes Irma and Maria.

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And we're doing it with this instrument to my right,

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which is called G-LiHT.

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G-LiHT stands for Goddard's Lidar, Hyperspectral, and Thermal instrument.

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And it’s using multiple sensors to actually understand

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more about terrestrial ecosystems

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Narrator: G-LiHT is installed on a small airplane

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and flown at low altitudes to collect lots of measurements in one pass.

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Bruce:  The lidar is being used to measure changes

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in the structure of the forest canopy,

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how many branches were lost, how many trees were knocked over,

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but we're also using other sensors that measure things

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such as how much, or what changes in the amount of sunlight

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that's being absorbed by these canopies and

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how that's affecting their photosynthesis and growth these days.

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Narrator: The lidar sends out five hundred thousand laser pulses

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each second and can detect the physical structure of individual trees.

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Doug: That laser energy from our lidar system

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will intersect the top of the canopy,

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smaller branches on the way down,

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and all the way down to this understory vegetation on the ground

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to help us construct a three-dimensional model of these forests

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Narrator:  But even though G-LiHT collects several types of data,

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it's not enough to fully understand how forests react to changes.

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Measurements from the ground level are a necessary complement.

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Doug:  The same laser technology on G-LiHT

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can be put on a tripod on the ground

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and make very detailed measurements of individual trees,

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the vines and lianas that hang from those trees

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as well as the damage that's occurred.

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Bruce: This is a partnership and it involves

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both the data from the ground,

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but also the data from the airborne instrument,

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as well as data from the satellite.

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So we call this scaling, when we can scale

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for ground measurements all the way up to satellites,

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and it just helps us understand what is going on from a larger picture. 

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Doug:   By being able to take information about the changes

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and the recovery of these landscapes over time,

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we're able to connect the changes in the carbon cycle,

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the changes in tropical forests and their functioning,

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even the changes in the strength and intensity of hurricanes

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and understand how those changes observed today

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help us understand and predict tomorrow's changes

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as well as the imprint of that hurricane

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in our atmosphere world-wide.

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[ beeping ]

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