WEBVTT

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Susan: If you've ever spent time looking
at satellite imagery of our planet, you

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might think that we know everything there
is to know about the shape and depth

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or bathymetry of the global seafloor.

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After all, you can see details
like canyons and seamounts.

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But what happens when you zoom in?

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These features begin to blur.

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The reality is, we don't yet have.

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A complete and detailed map of
our planet's ocean floor, all 360

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million square kilometers of it.

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But more detailed maps of the seafloor
are essential in our modern world.

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Understanding the shape and depth
of the seafloor has implications

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for everything from safe navigation
to ecosystem management and better

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understanding of Earth's climate system.

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To create high resolution maps that
reveal underwater terrain in greater

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detail, Ocean explorers often use
a tool called multibeam sonar.

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Here to tell us more is Derek
Sowers, mapping operations manager

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for Ocean Exploration Trust.

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So Derek, we're here today to talk
a bit about multibeam sonar mapping.

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Can you tell us a bit about how
multibeam sonar generally works?

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Derek: Yeah, so with any sonar,
essentially we're measuring

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the two way travel time.

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We send a, uh, acoustic pulse,
a sound signal from the ship

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down to the seafloor, it bounces
back and we listen for the echo.

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If we measure that two way travel
time, we can derive the depth of

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the seafloor underneath the ship.

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So that's generally how the sonar works.

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For a multi beam sonar essentially
you're doing that with many

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individual beams that are kind of
in a fan shape underneath the ship.

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A good analogy for a multibeam
sonar is basically a line of lasers

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in a row, moving along and sort of
scanning the seafloor and building a

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map of the terrain as it moves along.

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But instead of light, we're
using sound to do that.

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Susan: I understand that one of
the benefits of multibeam sonar

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is that we can get incredible
detail through high resolution.

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Um, can you tell us what that

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Derek: means?

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When most people look on Google
Earth, they see that, oh, it looks

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like the ocean's already been mapped.

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We know where everything is.

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But it's really a matter
of scale and resolution.

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So as you zoom in on those maps,
you'll see that you don't really have

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fine detail like you would on land.

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We can get a general sense of the
shape of the oceans from measurements

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made by satellites orbiting the Earth,
but those are limited to between two

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and four kilometers in resolution.

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When you map from a ship using a multibeam
sonar, you can map places in the deep

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sea to more like 50 meters resolution, so
a much clearer picture of the seafloor.

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Susan: So how much of the seafloor
has been mapped to that resolution?

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Derek: Only about 25 percent thus far.

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Um, so we're talking about publicly
available data, um, but with collected

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with a modern multibeam system.

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So we have a long way to go.

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So 75 percent of the world's ocean is
still really to be explored and mapped in

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this kind of detail for the first time.

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And then if you want to get even closer
with that, either towing something

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that has a sonar on it or putting
down a vehicle like a submersible

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that can get really close to the
seafloor, uh, you can map, uh, down

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to a centimeter scale level and really
reveal all the nooks and crannies.

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Susan: Wow.

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That's amazing.

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So I've heard we have better maps of
Mars than we do of our own sea floor.

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Is that true?

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Derek: It is true.

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And the main reason that is true is
because we can directly visualize

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the surface of Mars through the
imagery we can gather, whereas we

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can't actually directly see the
seafloor because we have these giant

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beautiful oceans obstructing our view.

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So the way we have to see the seafloor
on Earth is to use sound through the

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sonars that we've been discussing.

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Susan: So, as you've said, So much of the
ocean isn't mapped to high resolution,

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and there's so much still to be explored.

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It's going to take us years to do this.

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Why is high resolution mapping so

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Derek: important?

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For one thing, the oceans cover 71 percent
of our planet, so if we don't have a good

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map for the majority of that then we're
really missing out on understanding our

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planet and how it's evolved over time and
the processes that are continuing to shape

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our planet, such as new seafloor being
created, old seafloor being subducted

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into the trenches and disappearing,
being recycled back into the earth.

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Um, this ties in with, uh,
geologic hazards, natural hazards,

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such as tsunamis, underwater
landslides, earthquakes.

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So these are things that really affect the
safety of the coastal zone for many of us.

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Any infrastructure we put in the ocean,
we need to have good maps so we can

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do proper sighting of things like wind
farms or telecommunication cables.

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And then more in terms of understanding
the ecosystem of the ocean.

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If we don't have a good base map, then
that's kind of the fundamental first step

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of understanding the marine environment,
understanding marine habitats, what

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species can live where, and, you
know, that's, we can't even begin to

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do that without a map to begin with.

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Susan: Can you tell us a bit
about how multibeam sonar

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fits into the full exploration
strategy, the modern exploration

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Derek: strategy?

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Sure, yeah, it's a great question.

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I mean, I think it's basically,
uh, multibeam sonar mapping

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is considered, like, the first
step in exploring the ocean.

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So, you've got to go out and
get a good base map before

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you do further exploration.

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And then, that map usually reveals The
logical next step, so you'll usually

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make discoveries of interesting features,
new terrain that you didn't expect to

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see, or maybe you are searching for a
specific feature, you want to see where

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you think deep sea corals are going to
be, or undersea volcano, or a shipwreck

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that you discover, so you usually reveal
those things through mapping, and then the

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next step is to go and explore features
of interest in more detail using things

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like remotely operated vehicles, or
autonomous underwater vehicles, that's

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giving you that close up imagery, and
better understanding and the ability

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to take biological or geological
samples, you know, to further understand

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what's going on in these ecosystems.

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Susan: Derek, how do you decide
where you're going to map?

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Derek: We're putting a lot of effort into
exploring America's undersea territory.

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So there's about 3 billion acres that we
have yet to explore that's actually U.

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S.

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territory.

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So it's really like doing the Lewis
and Clark expedition, except about

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six times over and underwater.

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It's a huge mission.

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We're part of that effort.

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That's a NOAA wide initiative as
well to go out and explore our

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own country's undersea territory.

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And beyond that, we're interested in
the rest of the world's oceans as well.

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So, we decide those priorities mostly
in consultation with scientists

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around the world that really have
driving science questions, wanting

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to understand and expand our
knowledge of the marine environment.

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It's important as an exploration
program, we're trying to go to

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places that haven't been explored.

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Our mission is to go get the first look
at places where we know almost nothing.

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Susan: What's one of the biggest
surprises you've ever had, uh, in mapping

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Derek: the seafloor?

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Uh, I think one of the biggest surprises
I personally had was one of my first

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mapping expeditions that I was leading.

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I was, uh, off the southeast U.

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S.

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coast, so not far off one of the
most populated parts of the U.

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S.

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Uh, and we had known there was deep
sea coral mounds out there, but the

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full extent had never been mapped yet.

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And so, this one expedition I was
just shocked at the number of mounds,

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we found thousands and thousands
of mounds in just like 10 days of

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mapping with the deep water multibeam.

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So really, just seeing this vast landscape
that would probably be a national

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park if it was unlanded, honestly.

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You just never know what
you're going to find.

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So yeah, there's many,
many stories like that.

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So that

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Susan: said, Derek, what do you
see as the future for mapping

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Derek: the seafloor?

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I think we'll greatly see an expansion
of the use of uncrewed systems to map

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larger areas more quickly with a lower
carbon footprint and in higher resolution.

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So this will reveal a whole
new level of understanding

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of what our oceans look like.

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We'll have much greater insights into
the habitat they provide for life on

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Earth, and hopefully we become better
stewards of the marine environment

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with all this new understanding.

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Susan: Excellent goal.

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Thank you for your time and for what you

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Derek: do for a living.

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My pleasure.

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Thanks for the interview.