NASA Satellite Measuring Global Sea Level Rise : Short Wave A new satellite, scheduled to launch this weekend, is the latest in a parade of missions to measure sea level rise. As climate reporter Rebecca Hersher explains, it's vital data for scientists trying to understand how global warming is affecting the Earth's oceans.

For more, you can also read Rebecca's story, "NASA Satellite To Measure Global Sea Level Rise."

Email the show at shortwave@npr.org.
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Measuring Sea Level Rise From Space

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Measuring Sea Level Rise From Space

Measuring Sea Level Rise From Space

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MADDIE SOFIA, HOST:

You're listening to SHORT WAVE from NPR.

Climate reporter Rebecca Hersher, what do you got for me today?

REBECCA HERSHER, BYLINE: Oh, I have something good.

SOFIA: OK.

HERSHER: I've got a satellite. It's a new one, and it's scheduled to launch this weekend.

SOFIA: OK, cool. What's it going to do up there - like, space stuff?

HERSHER: Not really, actually.

SOFIA: OK.

HERSHER: This satellite will basically just stare at the ocean all day and try to figure out the exact location of the water.

SOFIA: OK. I guess that sounds fascinating, question mark.

HERSHER: Yeah, that's generous. It is actually fascinating, though. You know, scientists are really excited about this, especially climate scientists and especially, especially climate scientists who study how global warming affects the oceans and vice-versa because satellite data is really crucial for their work. It is the only way to understand what's happening to all the oceans, including remote parts that are harder to measure in other ways, like with ships.

SOFIA: All right. So today on the show, how this one new satellite could be huge for climate science and you, whether you live near an ocean or not. I'm Maddie Sofia, and this is SHORT WAVE from NPR.

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SOFIA: OK, Hersher, fill me in. Why do scientists care so much about this satellite set to launch this weekend?

HERSHER: Well, you actually have to go back a little bit.

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GEORGE H W BUSH: We all know that human activities are changing the atmosphere in unexpected and in unprecedented ways.

SOFIA: Is that George H.W. Bush?

HERSHER: Yeah, 1990 - the first President Bush actually talked a fair amount about climate change. It was something that scientists had been publicly warning about at that point for decades. And climate scientists were looking for more government support for their research - you know, big-ticket items, things like using federal research ships to study what was happening in the Arctic, for example, and launching satellites that could measure what was happening on Earth from space, particularly the oceans because, as we said, the oceans - they are so vast that you can only study them in their entirety from space.

SOFIA: Got it.

HERSHER: And it's actually just a couple of years after that 1990 speech that we just heard that the first satellite launches that can measure sea level rise. And it was called TOPEX/Poseidon.

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UNIDENTIFIED PERSON: Since the earliest times when humans first beheld the seashore and set out in raft, sensible boats, the oceans have been a source of great mystery.

SOFIA: I remember the first time I beheld the seashore, Hersher, you know?

HERSHER: Yeah, that's a video that NASA made to celebrate the 10-year anniversary of the TOPEX/Poseidon satellite launch.

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UNIDENTIFIED PERSON: From its vantage point in space, some 1,300 kilometers or about 800 miles above the Earth's surface, TOPEX/Poseidon circles the globe once every 112 minutes.

SOFIA: OK, first of all, that video's fantastic. Second, what do they mean? They were circling the globe measuring what, exactly?

HERSHER: So - the height of the ocean's surface because by then, sea levels were already rising because of climate change. You know, ice was already melting in the 1990s. Global temperatures were rising, and sea levels were going up. So scientists were racing to make better climate models to predict what sea level rise would look like over time and help people prepare. This original satellite - it was a big step forward because it allowed them to see basically the whole earth at once.

SOFIA: Got it. OK, so this original satellite went up in the 1990s. Does this new one replace it?

HERSHER: It's actually been replaced multiple times. There were three more sea level rise satellites launched in the intervening years. And each one was a little better, which makes sense - maybe a little more accurate, a little more durable.

SOFIA: So this last satellite, the one that's about to launch - it must be, like, pretty good, right? They've been practicing for a while. How accurate is this thing?

HERSHER: It is really accurate. I talked to the lead scientist on the mission at Jet Propulsion Laboratory in California.

JOSH WILLIS: My name is Josh Willis, and I'm the lead NASA scientist for the Sentinel-6 Mission.

HERSHER: So Sentinel-6 is the name of the new satellite. Technically, it's Sentinel-6 Michael Freilich. It's named after a former NASA leader who is clearly extremely popular because apparently NASA doesn't really name things after people who are alive.

SOFIA: Right.

HERSHER: He was alive when they named it for him. He's since died. Anyway, I talked to Josh Willis about how accurate the satellite's sea level rise measurements are.

WILLIS: It's really kind of an incredible feat of technology. We can actually measure the water level with an accuracy of about one inch from 800 miles up.

SOFIA: That's wild, Hersher. Like, how?

HERSHER: It uses radar, actually.

WILLIS: A radar beam comes down out of the satellite. It bounces off that surface, and then it measures the signal coming back. And by figuring out how long it takes to go down and come back, you can tell how far away the water is.

SOFIA: And if you know how far the water surface is from the satellite, you can figure out how high the water is relative to, like, the land.

HERSHER: Yeah, exactly, exactly. So Sentinel-6 - you can imagine - it will crisscross nearly the whole Earth every ten days, making these really accurate measurements. And so if you're a scientist, you can use all that data to get a really detailed picture of how high the oceans are and how that height is changing over time.

Here's the thing - Sentinel-6 will be up there for five years, and there's already an identical satellite in the works that will launch when that time is up and do another five years. So it's 10 years of continuous, super-accurate data about how high the oceans are. And that right there - that is why climate scientists are so jazzed about this satellite.

SOFIA: Because scientists love reliable data.

HERSHER: Reliable, continuous data especially, because imagine - if you are trying to understand how quickly sea levels are rising, you need measurements every year for decades because climate change is a slow and steady catastrophe.

SOFIA: Yeah, I mean, we've talked about this on the show before. People definitely see evidence that sea levels are rising, like roads flooding during high tides, for example. But that's happened over the course of decades.

HERSHER: Yeah. And unless you're really paying attention, it's easy to miss what's happening until it's too late. So governments and citizens rely on climate models to tell them - to tell us - how quickly sea levels are rising around the world. And climate models are only as good as the data that go into them.

SOFIA: What about people who don't live near the coast, though? Like, it seems like this would matter less to their lives.

HERSHER: Yeah, that's a logical assumption.

SOFIA: Thank you.

HERSHER: Oh, it's also very wrong.

SOFIA: (Laughter) OK, a little rude, but go on.

HERSHER: I mean, Maddie, what happens in the ocean doesn't stay in the ocean. Do you know how big the oceans are? They're huge. They're so big. They're so much bigger than the land. So as the oceans change and rise, it affects the whole climate all over the world.

I'll give you an example. I talked to an oceanographer at the University of Washington, LuAnne Thompson, about this exact thing. She uses sea level rise data from the previous satellites.

LUANNE THOMPSON: I use that data every day in my research.

HERSHER: And she says she'll definitely use the data from the new satellite, Sentinel-6. But she's studying things way bigger than just how high the water level is in Seattle's harbor, for example.

THOMPSON: We can also use the sea level measurements to understand how currents are changing, how the ocean is storing heat.

HERSHER: So the oceans - they've soaked up more than 90% of the extra heat that greenhouse gases have trapped in the atmosphere. If you want to understand how hot the Earth will get in the next few decades, you have to understand how much more heat the ocean will absorb.

SOFIA: But why would it be helpful for somebody like this scientist to know how high sea levels are if she's trying to understand how much heat the ocean is soaking up?

HERSHER: Right. I was initially kind of confused by this, too. And the key is because water expands when it gets hotter, right?

SOFIA: Yeah, of course.

HERSHER: So as ocean water heats up and expands, the surface rises. It's one reason for sea level rise. Obviously, melting ice is another. So Thompson is using sea level rise data to figure out how much heat the ocean has already soaked up, how much heat it might soak up in the future and where the extra water is coming from, like glaciers versus ice caps, for example, things like that. And to study all of that, you need accurate, continuous sea level rise data.

SOFIA: OK. I see why these climate scientists are getting excited. Like, I'm getting a little excited right now...

HERSHER: (Laughter).

SOFIA: ...Like I do with any climate story - excited and alarmed, as usual, you know?

HERSHER: Yeah. Yeah.

SOFIA: So when is the satellite launching?

HERSHER: Well, we're taping this episode on Thursday the 19. And right now, it's scheduled to launch on Saturday, November 21 from California. That's assuming the weather is good. It's already been rescheduled once, this launch.

SOFIA: OK, well, this is exciting. I'll be watching.

HERSHER: Yeah, me too.

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SOFIA: This episode was produced by Thomas Lu, edited by Viet Le and fact-checked by Ariela Zebede (ph). If you don't already, I highly recommend following NPR's Instagram account. Our colleagues will be sharing a story about the Sentinel-6 satellite after it launches. I'm Maddie Sofia, and you're listening to SHORT WAVE from NPR.

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