Susan: If you've ever spent time looking at satellite imagery of our planet, you
might think that we know everything there is to know about the shape and depth
or bathymetry of the global seafloor.
After all, you can see details like canyons and seamounts.
But what happens when you zoom in?
These features begin to blur.
The reality is, we don't yet have.
A complete and detailed map of our planet's ocean floor, all 360
million square kilometers of it.
But more detailed maps of the seafloor are essential in our modern world.
Understanding the shape and depth of the seafloor has implications
for everything from safe navigation to ecosystem management and better
understanding of Earth's climate system.
To create high resolution maps that reveal underwater terrain in greater
detail, Ocean explorers often use a tool called multibeam sonar.
Here to tell us more is Derek Sowers, mapping operations manager
for Ocean Exploration Trust.
So Derek, we're here today to talk a bit about multibeam sonar mapping.
Can you tell us a bit about how multibeam sonar generally works?
Derek: Yeah, so with any sonar, essentially we're measuring
the two way travel time.
We send a, uh, acoustic pulse, a sound signal from the ship
down to the seafloor, it bounces back and we listen for the echo.
If we measure that two way travel time, we can derive the depth of
the seafloor underneath the ship.
So that's generally how the sonar works.
For a multi beam sonar essentially you're doing that with many
individual beams that are kind of in a fan shape underneath the ship.
A good analogy for a multibeam sonar is basically a line of lasers
in a row, moving along and sort of scanning the seafloor and building a
map of the terrain as it moves along.
But instead of light, we're using sound to do that.
Susan: I understand that one of the benefits of multibeam sonar
is that we can get incredible detail through high resolution.
Um, can you tell us what that
Derek: means?
When most people look on Google Earth, they see that, oh, it looks
like the ocean's already been mapped.
We know where everything is.
But it's really a matter of scale and resolution.
So as you zoom in on those maps, you'll see that you don't really have
fine detail like you would on land.
We can get a general sense of the shape of the oceans from measurements
made by satellites orbiting the Earth, but those are limited to between two
and four kilometers in resolution.
When you map from a ship using a multibeam sonar, you can map places in the deep
sea to more like 50 meters resolution, so a much clearer picture of the seafloor.
Susan: So how much of the seafloor has been mapped to that resolution?
Derek: Only about 25 percent thus far.
Um, so we're talking about publicly available data, um, but with collected
with a modern multibeam system.
So we have a long way to go.
So 75 percent of the world's ocean is still really to be explored and mapped in
this kind of detail for the first time.
And then if you want to get even closer with that, either towing something
that has a sonar on it or putting down a vehicle like a submersible
that can get really close to the seafloor, uh, you can map, uh, down
to a centimeter scale level and really reveal all the nooks and crannies.
Susan: Wow.
That's amazing.
So I've heard we have better maps of Mars than we do of our own sea floor.
Is that true?
Derek: It is true.
And the main reason that is true is because we can directly visualize
the surface of Mars through the imagery we can gather, whereas we
can't actually directly see the seafloor because we have these giant
beautiful oceans obstructing our view.
So the way we have to see the seafloor on Earth is to use sound through the
sonars that we've been discussing.
Susan: So, as you've said, So much of the ocean isn't mapped to high resolution,
and there's so much still to be explored.
It's going to take us years to do this.
Why is high resolution mapping so
Derek: important?
For one thing, the oceans cover 71 percent of our planet, so if we don't have a good
map for the majority of that then we're really missing out on understanding our
planet and how it's evolved over time and the processes that are continuing to shape
our planet, such as new seafloor being created, old seafloor being subducted
into the trenches and disappearing, being recycled back into the earth.
Um, this ties in with, uh, geologic hazards, natural hazards,
such as tsunamis, underwater landslides, earthquakes.
So these are things that really affect the safety of the coastal zone for many of us.
Any infrastructure we put in the ocean, we need to have good maps so we can
do proper sighting of things like wind farms or telecommunication cables.
And then more in terms of understanding the ecosystem of the ocean.
If we don't have a good base map, then that's kind of the fundamental first step
of understanding the marine environment, understanding marine habitats, what
species can live where, and, you know, that's, we can't even begin to
do that without a map to begin with.
Susan: Can you tell us a bit about how multibeam sonar
fits into the full exploration strategy, the modern exploration
Derek: strategy?
Sure, yeah, it's a great question.
I mean, I think it's basically, uh, multibeam sonar mapping
is considered, like, the first step in exploring the ocean.
So, you've got to go out and get a good base map before
you do further exploration.
And then, that map usually reveals The logical next step, so you'll usually
make discoveries of interesting features, new terrain that you didn't expect to
see, or maybe you are searching for a specific feature, you want to see where
you think deep sea corals are going to be, or undersea volcano, or a shipwreck
that you discover, so you usually reveal those things through mapping, and then the
next step is to go and explore features of interest in more detail using things
like remotely operated vehicles, or autonomous underwater vehicles, that's
giving you that close up imagery, and better understanding and the ability
to take biological or geological samples, you know, to further understand
what's going on in these ecosystems.
Susan: Derek, how do you decide where you're going to map?
Derek: We're putting a lot of effort into exploring America's undersea territory.
So there's about 3 billion acres that we have yet to explore that's actually U.
S.
territory.
So it's really like doing the Lewis and Clark expedition, except about
six times over and underwater.
It's a huge mission.
We're part of that effort.
That's a NOAA wide initiative as well to go out and explore our
own country's undersea territory.
And beyond that, we're interested in the rest of the world's oceans as well.
So, we decide those priorities mostly in consultation with scientists
around the world that really have driving science questions, wanting
to understand and expand our knowledge of the marine environment.
It's important as an exploration program, we're trying to go to
places that haven't been explored.
Our mission is to go get the first look at places where we know almost nothing.
Susan: What's one of the biggest surprises you've ever had, uh, in mapping
Derek: the seafloor?
Uh, I think one of the biggest surprises I personally had was one of my first
mapping expeditions that I was leading.
I was, uh, off the southeast U.
S.
coast, so not far off one of the most populated parts of the U.
S.
Uh, and we had known there was deep sea coral mounds out there, but the
full extent had never been mapped yet.
And so, this one expedition I was just shocked at the number of mounds,
we found thousands and thousands of mounds in just like 10 days of
mapping with the deep water multibeam.
So really, just seeing this vast landscape that would probably be a national
park if it was unlanded, honestly.
You just never know what you're going to find.
So yeah, there's many, many stories like that.
So that
Susan: said, Derek, what do you see as the future for mapping
Derek: the seafloor?
I think we'll greatly see an expansion of the use of uncrewed systems to map
larger areas more quickly with a lower carbon footprint and in higher resolution.
So this will reveal a whole new level of understanding
of what our oceans look like.
We'll have much greater insights into the habitat they provide for life on
Earth, and hopefully we become better stewards of the marine environment
with all this new understanding.
Susan: Excellent goal.
Thank you for your time and for what you
Derek: do for a living.
My pleasure.
Thanks for the interview.