France 447: How scientists found a needle in a haystack


Maggie Koerth-Baker at 7:59 AM Friday, May 6, 2011



The cockpit voice recorder from Air France 447, as it was found at the
bottom of the Atlantic Ocean.


Last weekend, investigators announced that they had recovered the flight
data recorder from the wreckage of Air France 447-a jetliner that crashed in
the deep Atlantic two years ago. But, while the discovery of the data
recorder is recent, the story of how Flight 447 was found goes back a month.


This year's search was the fourth attempt to find the wreckage of Flight
447, and it probably would have been the last, even if the plane hadn't been
found. Previous searches had been done by boat, mini-sub, and-back when
there was still a chance of catching the audio signal from the plane's black
boxes-underwater acoustic sensors. In 2010, scientists from the Woods Hole
Oceanographic Institute were brought in to search for the crash site using
autonomous robot subs. Still nothing had been found.


On March 22, 2011, the Woods Hole team set out from Brazil to try again.
They'd barely been at the search location for a week when they found what
they were looking for. On April 3, researchers spotted the plane's debris
field, 13,000 feet down, smack in the middle of a massive underwater
mountain range.


The success was astounding, but I wanted to know ... what made this search
different from the others? What could the team from Woods Hole do that other
groups could not, and how did their system work? To find out, I spoke with
Mike Purcell, senior engineer with Woods Hole, and the chief of sea search
operations for the mission.


Maggie Koerth-Baker: Your team found Flight 447 with the help of an
autonomous submarine called the Remus 6000. Can you tell me a little about
the history of that sub? What could the Remus 6000 do that previous systems
couldn't?


Mike Purcell: The first one was developed in 2001. Really, they have a
greater depth limit. There are no other deep water subs that can go to 6000
meters. That's one way it's unique. Also, between the six Remus 6000's that
exist out in the world right now, there's probably been more missions done
with a Remus 6000 than any other deep water AUV.


To do a search, the Remus 6000 gets a mission program, a track line to swim.
It goes into the water and uses various naviagtion techniques to swim the
track line. There isn't anybody actively controlling it. But it's also not
as smart as you might thing. It's not making decisions based on terrain,
other than staying some fixed altitutude off the bottom. It can't go around
things or avoid stuff that might be in front of it. It does go up over
mountain ridges, but the Remus 6000s do sometimes run into things, too. They
don't have the full sensor capacity and independent thinking to make
decisions that some totally autonamous robot might. One reason that's the
case-it's just harder to do that in the water than in the air. We're really
limited to one kind of sensor, acoustic sensors, underwater.


MKB: What kind of research do Remus 6000 subs normally work on? Was this
search different in any way, from a technological or logistics perspective?


MP: Our lab ... we've been involved in the development of AUVs. We've been
making the newer and better ones over the last 15 years. It was only in
about 2008 that we started getting involved in operations. We purchased a
couple Remus 6000s and we're the operators. They were involved in search for
Amelia Earhart's airplane. We did some localization of deep corals in Gulf
Stream off of Florida. We mapped the Titanic site with AUV's last year. And
then we've now worked on the Air France survey twice, once in 2010 and once
in 2011.

Even when we've done these searches for the airplanes there's been a
tremendous amount of data collected, and that's been made available, or will
be made available in the future, to the science community. What kinds of
things can people do with seafloor data? I'm not a geologist, so I'm not
totally sure what they might do. But a lot of the seafloor is totally
unexplored. We've got about 1500 square miles mapped. And I think there's a
lot of interesting geography there in the Mid-Atlantic Ridge where we did
this search.


MKB: How many people involved in running one of these searches, and what do
they do?


MP: We had three vehicles out there. When we're running three vehicles we
have 12 people, working in two 12-hour shifts. There's six people on each
shift. And they're doing things like getting the vehicles in and out of the
water. Reprogramming the vehicles. Tracking the vehicles. There's usually
two AUVs in the water at all times. And there's a guy who is dedicated to
processing the data.


MKB: The Remus 6000s had previously been involved in the search for Air
France 447, but hadn't found it before. Was there a major location change,
or some other shift in how the search was done this time around? Were you
involved in deciding where the search would happen?


MP: We were out there first in 2010, and there'd been a pretty big modeling
study that guided the search then. Of the entire area, which is 17,000
square kilometers, 7,000 had been what we were search going into this year.
The plan was to search it all. There was one difference, we just decided to
start close to the last known position of the plane, instead of further away
from it. The BEA [Ed: Bureau d'Enquêtes et d'Analyses, the French air safety
investigators] identified three search zones, big areas that they wanted us
to do in order, and then, from there, we sort of had the freedom to decide
where we start in those areas. So we started out based on where we left off
last year.


MKB: The mid-ocean ridge, where the search was conducted, has been described
as something like an underwater Himalayan mountain range. A lot of reports
I've read on it made it sound very foreboding and not like a place where it
would be possible to find anything. But WHOI has been doing research on the
mid-ocean ridge for decades. Is the scary reputation deserved? What
challenges do you face doing research in that location, as an organization
that has experience with it?


MP: So, I think this mission was different for us in that we were trying to
search such a huge area. We needed our vehicles to swim up and down those
mountains. The water out there was 4000 meters meters deep at the deepest
spot and very close to that was where we found the wreckage. But just a few
miles away it was only 2000 meters meters deep. There are some very steep
mountains.

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