The search for MH370: Why can’t we find it?
For all our state-of-the-art imaging technology, we are better at searching the surface of the Moon than the depths of the ocean. Philip Dooley looks at how science has measured up to the task of finding the Malaysian aircraft.
“I’m now optimistic we’ll find the aircraft, or what's left of the aircraft, in the not too-distant future,” Air Chief Marshal Angus Houston told the world at a morning news conference last Wednesday.
Houston, the dour former Australian Defence Force chief, is heading the search for Malaysian Airlines flight MH370, which disappeared in the early hours of 8 March. He gave his “optimistic” assessment after Australian defence vessel Ocean Shield picked up sonar pings believed to be from the plane’s black box. But in the month since the plane vanished, hopes that the search would soon be over have been raised several times only to be dashed. Will Houston’s latest announcement turn out to be too optimistic?
In this age of remote sensing, our skies saturated with satellites so sensitive they can see us throw a prawn on the barbecue, it seems inconceivable to lose something as big as a Boeing 777. It turns out our instruments are no match for the vast and impenetrable expanse that is the southern Indian Ocean – it is the very worst place to lose a plane.
In the first few days after flight MH370 went missing shortly after taking off from Kuala Lumpur en route to Beijing, the world was offered the incredible news that the plane had simply disappeared. Satellites were not much help - they are effectively blind at night when MH370 flew. In the morning the satellites were watching again, but alas they do not record their viewings over the ocean. If they routinely did, they would rapidly run out of data storage space. All that the world had to go on was the last message from the captain as they crossed into Vietnamese airspace over the South China Sea “Good night Malaysian three seven oh.”
The ocean is essentially impenetrable to light. By the time it reaches
300 meters beneath the surface it has been completely absorbed.
After four days, technicians at British telecommunications satellite operator Inmarsat had managed to analyse the hourly signal "handshakes" with the aeroplane, which had continued after MH370’s other systems were manually switched off. Using the strength of the signals and their travel time, Inmarsat's technicians were able to work out how far the aircraft was from the satellite and draw an arc of possible locations. The shocking conclusion was that the plane was absurdly off course. The only possible parts of the arc that a Boeing 777 could have reached in that flying time were either northwest into Central Asia, or southwards into the Indian Ocean.
As fears of involvement by Central Asian extremists grew, Inmarsat realised that the pings from the aircraft carried more information than was initially thought and initiated a deeper analysis. This relied on the Doppler effect, the change in pitch that is heard when a vehicle sounding a siren approaches and passes an observer. The explanation for this phenomenon is that the sound waves coming from the siren are stretched apart as their source moves away from the listener. The radio waves emitted in MH370’s pings were subject to this same effect and from the amount of stretch in the waves, Inmarsat technicians were able to calculate the direction the aeroplane was moving relative to their satellite, and discount the northern arc.
Assuming that the plane had continued until its fuel ran out, its final resting place was apparently somewhere off the coast of Western Australia, about 2,000 km from Perth. The new focus of the search became the stormy and remote southern Indian Ocean.
It turns out it's easier to study the Moon than the depths of the ocean. It is essentially impenetrable to light. Blue light penetrates farthest but by 300 meters beneath the surface it has been completely absorbed – leaving a black abyss of more than 4 km to where the remains of MH370 are believed to be lying.
Once the Inmarsat’s Doppler calculation pinpointed the Indian Ocean, the focus immediately switched to satellite image analysis in the hope of finding surface wreckage. Although satellites such as DigitalGlobe’s WorldView-1 can collect a million square kilometres of imagery a day and pick out objects the size of a backpack, finding the wreckage of a lost plane is still a big ask. For one thing, there are plenty of blind spots because satellites can’t generally see through clouds. And then there are general problems of a-needle-in-a-haystack kind.
The sheer volume of images generated amounts to petabytes (more than a million gigabytes) of data. “You can’t image the entire Indian Ocean and send all that imagery back,” says Andrew Dempster, Director of the Australian Centre for Space Engineering Research.
To help sift through even a filtered pile of data, the public was called in to help. Crowdsourcing site Tomnod engaged more than seven million volunteers who looked at 800 million images and identified 6.7 million “features” that were potentially debris from the plane. Many of those turned out to be white caps from rough seas or unrelated rubbish of which there is plenty – every square kilometre of ocean harbours an estimated 10 large pieces of floating garbage.
Aircraft also combed the area inspecting floating material but none of it belonged to the aircraft. “If MH370 debris were there you’d think they would have found it by now,” says Dempster. It is this absence of evidence that points to what is now the leading theory, MH370 crashed into the ocean without breaking up.
And that has led to the final stage of the search, combing the depths of the vast, black Indian ocean with the only tool that can penetrate it - sonar. It is listening for the SOS signal from MH370’s “black box” flight recorder, which is fitted with an acoustic beacon that activates on contact with water.
When it comes to tracing the source of the pings, sonar is less than perfect. Changes in the density of the water, influenced by temperature and salinity, can interfere with the sound waves. “Keep in mind too that the temperature and salinity change at different depths,” says Helen McGregor, an oceanographer at the Australian National University.
And appropriately for a final act, there’s the drama of the dying batteries of the black box. They are only designed to last for 30 days, after which the signal strength quickly fades. They are already past that date. In painful juxtaposition, sonar detection devices are excruciatingly slow. Unlike the swift sweeps made by spotter planes, sonar beacon detectors must be towed in the water behind a ship at less than 5 knots (9.3 kph). By one estimate, it would take six years to search the 216,000 square kilometre target area.
But the Inmarsat satellite has continued to narrow the search area based on finer analyses of the pings from the flying plane. Despite the unlikely odds, search vessels have detected snatches of sonar that seem to be from the MH370 acoustic beacon.
Will Air Chief Marshal Houston’s optimism prove well placed? Even if the search teams can pinpoint the wreckage, the mystery surrounding Flight MH370 might not be solved soon. It took two years to locate and recover the flight recorders from the Air France Flight 447 that crashed in the Atlantic Ocean on 1 June 2009, even though the first wreckage of the aircraft was found within five days. We may still have a long wait to discover what took place on MH370 to carry it so far off course.