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  • I'm a radio glaciologist.

  • That means that I use radar to study glaciers and ice sheets.

  • And like most glaciologists right now,

  • I'm working on the problem of estimating

  • how much the ice is going to contribute to sea level rise in the future.

  • So today, I want to talk to you about

  • why it's so hard to put good numbers on sea level rise,

  • and why I believe that by changing the way we think about radar technology

  • and earth-science education,

  • we can get much better at it.

  • When most scientists talk about sea level rise,

  • they show a plot like this.

  • This is produced using ice sheet and climate models.

  • On the right, you can see the range of sea level

  • predicted by these models over the next 100 years.

  • For context, this is current sea level,

  • and this is the sea level

  • above which more than 4 million people could be vulnerable to displacement.

  • So in terms of planning,

  • the uncertainty in this plot is already large.

  • However, beyond that, this plot comes with the asterisk and the caveat,

  • "... unless the West Antarctic Ice Sheet collapses."

  • And in that case, we would be talking about dramatically higher numbers.

  • They'd literally be off the chart.

  • And the reason we should take that possibility seriously

  • is that we know from the geologic history of the Earth

  • that there were periods in its history

  • when sea level rose much more quickly than today.

  • And right now, we cannot rule out

  • the possibility of that happening in the future.

  • So why can't we say with confidence

  • whether or not a significant portion of a continent-scale ice sheet

  • will or will not collapse?

  • Well, in order to do that, we need models

  • that we know include all of the processes, conditions and physics

  • that would be involved in a collapse like that.

  • And that's hard to know,

  • because those processes and conditions are taking place

  • beneath kilometers of ice,

  • and satellites, like the one that produced this image,

  • are blind to observe them.

  • In fact, we have much more comprehensive observations of the surface of Mars

  • than we do of what's beneath the Antarctic ice sheet.

  • And this is even more challenging in that we need these observations

  • at a gigantic scale in both space and time.

  • In terms of space, this is a continent.

  • And in the same way that in North America,

  • the Rocky Mountains, Everglades and Great Lakes regions are very distinct,

  • so are the subsurface regions of Antarctica.

  • And in terms of time, we now know

  • that ice sheets not only evolve over the timescale of millennia and centuries,

  • but they're also changing over the scale of years and days.

  • So what we want is observations beneath kilometers of ice

  • at the scale of a continent,

  • and we want them all the time.

  • So how do we do this?

  • Well, we're not totally blind to the subsurface.

  • I said in the beginning that I was a radio glaciologist,

  • and the reason that that's a thing

  • is that airborne ice-penetrating radar is the main tool we have

  • to see inside of ice sheets.

  • So most of the data used by my group is collected by airplanes

  • like this World War II-era DC-3,

  • that actually fought in the Battle of the Bulge.

  • You can see the antennas underneath the wing.

  • These are used to transmit radar signals down into the ice.

  • And the echos that come back contain information

  • about what's happening inside and beneath the ice sheet.

  • While this is happening,

  • scientists and engineers are on the airplane

  • for eight hours at a stretch,

  • making sure that the radar's working.

  • And I think this is actually a misconception

  • about this type of fieldwork,

  • where people imagine scientists peering out the window,

  • contemplating the landscape, its geologic context

  • and the fate of the ice sheets.

  • We actually had a guy from the BBC's "Frozen Planet" on one of these flights.

  • And he spent, like, hours videotaping us turn knobs.

  • (Laughter)

  • And I was actually watching the series years later with my wife,

  • and a scene like this came up, and I commented on how beautiful it was.

  • And she said, "Weren't you on that flight?"

  • (Laughter)

  • I said, "Yeah, but I was looking at a computer screen."

  • (Laughter)

  • So when you think about this type of fieldwork,

  • don't think about images like this.

  • Think about images like this.

  • (Laughter)

  • This is a radargram, which is a vertical profile through the ice sheet,

  • kind of like a slice of cake.

  • The bright layer on the top is the surface of the ice sheet,

  • the bright layer on the bottom is the bedrock of the continent itself,

  • and the layers in between are kind of like tree rings,

  • in that they contain information about the history of the ice sheet.

  • And it's amazing that this works this well.

  • The ground-penetrating radars that are used

  • to investigate infrastructures of roads or detect land mines

  • struggle to get through a few meters of earth.

  • And here we're peering through three kilometers of ice.

  • And there are sophisticated, interesting, electromagnetic reasons for that,

  • but let's say for now that ice is basically the perfect target for radar,

  • and radar is basically the perfect tool to study ice sheets.

  • These are the flight lines

  • of most of the modern airborne radar-sounding profiles

  • collected over Antarctica.

  • This is the result of heroic efforts over decades

  • by teams from a variety of countries and international collaborations.

  • And when you put those together, you get an image like this,

  • which is what the continent of Antarctica would look like

  • without all the ice on top.

  • And you can really see the diversity of the continent in an image like this.

  • The red features are volcanoes or mountains;

  • the areas that are blue would be open ocean

  • if the ice sheet was removed.

  • This is that giant spatial scale.

  • However, all of this that took decades to produce

  • is just one snapshot of the subsurface.

  • It does not give us any indication of how the ice sheet is changing in time.

  • Now, we're working on that, because it turns out

  • that the very first radar observations of Antarctica were collected

  • using 35 millimeter optical film.

  • And there were thousands of reels of this film

  • in the archives of the museum of the Scott Polar Research Institute

  • at the University of Cambridge.

  • So last summer, I took a state-of-the-art film scanner

  • that was developed for digitizing Hollywood films and remastering them,

  • and two art historians,

  • and we went over to England, put on some gloves

  • and archived and digitized all of that film.

  • So that produced two million high-resolution images

  • that my group is now working on analyzing and processing

  • for comparing with contemporary conditions in the ice sheet.

  • And, actually, that scanner -- I found out about it

  • from an archivist at the Academy of Motion Picture Arts and Sciences.

  • So I'd like to thank the Academy --

  • (Laughter)

  • for making this possible.

  • (Laughter)

  • And as amazing as it is

  • that we can look at what was happening under the ice sheet 50 years ago,

  • this is still just one more snapshot.

  • It doesn't give us observations

  • of the variation at the annual or seasonal scale,

  • that we know matters.

  • There's some progress here, too.

  • There are these recent ground-based radar systems that stay in one spot.

  • So you take these radars and put them on the ice sheet

  • and you bury a cache of car batteries.

  • And you leave them out there for months or years at a time,

  • and they send a pulse down into the ice sheet

  • every so many minutes or hours.

  • So this gives you continuous observation in time --

  • but at one spot.

  • So if you compare that imaging to the 2-D pictures provided by the airplane,

  • this is just one vertical line.

  • And this is pretty much where we are as a field right now.

  • We can choose between good spatial coverage

  • with airborne radar sounding

  • and good temporal coverage in one spot with ground-based sounding.

  • But neither gives us what we really want:

  • both at the same time.

  • And if we're going to do that,

  • we're going to need totally new ways of observing the ice sheet.

  • And ideally, those should be extremely low-cost

  • so that we can take lots of measurements from lots of sensors.

  • Well, for existing radar systems,

  • the biggest driver of cost is the power required

  • to transmit the radar signal itself.

  • So it'd be great if we were able to use existing radio systems

  • or radio signals that are in the environment.

  • And fortunately, the entire field of radio astronomy

  • is built on the fact that there are bright radio signals in the sky.

  • And a really bright one is our sun.

  • So, actually, one of the most exciting things my group is doing right now

  • is trying to use the radio emissions from the sun as a type of radar signal.

  • This is one of our field tests at Big Sur.

  • That PVC pipe ziggurat is an antenna stand some undergrads in my lab built.

  • And the idea here is that we stay out at Big Sur,

  • and we watch the sunset in radio frequencies,

  • and we try and detect the reflection of the sun off the surface of the ocean.

  • Now, I know you're thinking, "There are no glaciers at Big Sur."

  • (Laughter)

  • And that's true.

  • (Laughter)

  • But it turns out that detecting the reflection of the sun

  • off the surface of the ocean

  • and detecting the reflection off the bottom of an ice sheet

  • are extremely geophysically similar.

  • And if this works,

  • we should be able to apply the same measurement principle in Antarctica.

  • And this is not as far-fetched as it seems.

  • The seismic industry has gone through a similar technique-development exercise,

  • where they were able to move from detonating dynamite as a source,

  • to using ambient seismic noise in the environment.

  • And defense radars use TV signals and radio signals all the time,

  • so they don't have to transmit a signal of radar

  • and give away their position.

  • So what I'm saying is, this might really work.

  • And if it does, we're going to need extremely low-cost sensors

  • so we can deploy networks of hundreds or thousands of these on an ice sheet

  • to do imaging.

  • And that's where the technological stars have really aligned to help us.

  • Those earlier radar systems I talked about

  • were developed by experienced engineers over the course of years

  • at national facilities

  • with expensive specialized equipment.

  • But the recent developments in software-defined radio,

  • rapid fabrication and the maker movement,

  • make it so that it's possible for a team of teenagers

  • working in my lab over the course of a handful of months

  • to build a prototype radar.

  • OK, they're not any teenagers, they're Stanford undergrads,

  • but the point holds --

  • (Laughter)

  • that these enabling technologies are letting us break down the barrier

  • between engineers who build instruments and scientists that use them.

  • And by teaching engineering students to think like earth scientists

  • and earth-science students who can think like engineers,

  • my lab is building an environment in which we can build custom radar sensors

  • for each problem at hand,

  • that are optimized for low cost and high performance

  • for that problem.

  • And that's going to totally change the way we observe ice sheets.

  • Look, the sea level problem and the role of the cryosphere in sea level rise

  • is extremely important

  • and will affect the entire world.

  • But that is not why I work on it.

  • I work on it for the opportunity to teach and mentor

  • extremely brilliant students,

  • because I deeply believe that teams of hypertalented,

  • hyperdriven, hyperpassionate young people

  • can solve most of the challenges facing the world,

  • and that providing the observations required to estimate sea level rise

  • is just one of the many such problems they can and will solve.

  • Thank you.

  • (Applause)

I'm a radio glaciologist.

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TED】Dustin Schroeder: How we look kilometers below Antarctic ice sheet (How we look kilometers below Antarctic ice sheet | Dustin Schroeder) (【TED】Dustin Schroeder: How we look kilometers below the Antarctic ice sheet (How we look kilometers below the Ant

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    Zenn に公開 2021 年 01 月 14 日
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