ROBERT SIEGEL, HOST:
So to recap the satellite data about MH370, investigators have narrowed the area that offered the last hint of a plane in flight. We also know that satellites have taken pictures of objects floating in the Indian Ocean. What they were is still not clear. And in any case, there are still thousands and thousands of square miles of open ocean to search for it. And joining me to explain what we know is NPR's science correspondent Geoff Brumfiel. Hi, Geoff.
GEOFF BRUMFIEL, BYLINE: Hi.
SIEGEL: Let's start with the satellite data. How did they figure out where the plane went?
BRUMFIEL: Well, so first, just to recap, this is the most reliable data we've had about this plane so far. Basically, a company called Inmarsat communicates with commercial aircraft in flight, and they were picking up simple pings from this airplanes for several hours after it disappeared from Malaysian radar. Now, they used these pings previously to narrow the search to a northern arc they extended to Central Asia and a southern arc that went down into the Indian Ocean.
Today, they said they knew it was the southern arc. And they said they knew this using a technique called Doppler shift. So this is something like if you've ever heard an ambulance go by or a race car, you know, goes vroom. So it starts out high and goes low. Similarly, the radio signals from this plane shifted and they could use that to tell roughly where it went.
They compared the signals to planes that flew south and planes that flew north, and it pretty unambiguously showed the plane flew south.
SIEGEL: But the south is a lot of ocean. Can they narrow it down any further?
BRUMFIEL: No. This is as far as the satellite data goes. The search now has to go to the open ocean, and they have to try and locate some debris from this aircraft.
SIEGEL: Well, once they have a rough search area, how do they go about finding a plane under water?
BRUMFIEL: Well, the second thing they have to do - once they've done that, they have to look for pings from the airplane. This is a different kind of ping. It's emitted by the airplane's black box. And it's an actual sound that can be heard underwater. The U.S. Navy is flying equipment down there right now that can hear these pings at depths of up to 20,000 feet.
The problem is that the ping - the device that can hear the pings can only move at a few miles an hour. They've got many, many thousands of miles to search. And the pings coming from the black boxes on this airplane only last for about 30 days. We're about 15 days in now, so there's only about two weeks left.
I spoke to Colleen Keller. She's at a company called Metron, which helped to locate the Air France flight 447 that went down in the Atlantic Ocean in 2009. Here's what she said about trying to find it.
COLLEEN KELLER: We might get lucky. We might hear something. But chances are, we're not going to. If we don't, I don't know where we start. I mean, you could put remotely controlled subs down there with cameras all you want, but it's a very low probability we would see something.
SIEGEL: That's not very encouraging. They say it's phenomenally hard. Is there any way to narrow the search?
BRUMFIEL: Well, maybe. Actually Keller's company was part of the investigation, as I said, and they used statistics to try and narrow the search area. Basically, they took every piece of data they could find on the Air France flight - flight data, data about currents in the ocean, data about previous air crashes and how far planes flew before they hit the ground. And they used all that data together to create a model that had a probabilistic distribution.
Eventually, that model was able to find the flight, but it took two years. And this is, obviously, a much, much larger search area than that Air France flight.
SIEGEL: OK. Thank you, Geoff.
BRUMFIEL: Thank you.
SIEGEL: That's NPR's Geoff Brumfiel. Transcript provided by NPR, Copyright NPR.