Cutting-edge methods in search for flight MH370
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| British firm Inmarsat compared data sent back from flight MH370 with similar aircraft
The British satellite telecommunications company Inmarsat has now pretty much confirmed what the world had feared - that Malaysia Airways flight MH370 was surely lost in the southern Indian Ocean, south-west of Australia.
The satellite operator was receiving hourly "pings" from equipment on board the plane for at least five hours after the aircraft left Malaysian airspace.
Initially, these pings - which were essentially just "I'm switched on" messages - were used to plot two broad arcs of possible travel - one arc going to the north, the other heading south.
The northerly route always looked doubtful because it would have taken the plane towards countries with sophisticated air-defence systems. The chances of it avoiding detection seemed slim.
Inmarsat, which is feeding into the official investigation, spent the weekend reviewing all of its flight MH370 data.
Doppler effect
In particular, it examined the frequency spectrum of the ping transmissions and how they differed from pings emitted by previous Malaysia Airlines Boeing 777 flights.
This allowed engineers to model how the frequency might change very slightly as a plane travels through the sky.
This is the famous Doppler effect, which acts to "stretch" or "compress" radio waves emanating from moving objects. With a moving police car, the equivalent sound effect is to change the pitch of the siren.
The analysis is cutting-edge and has never been done before, but it has enabled Inmarsat's engineers to confirm that the southerly arc was the path taken by flight MH370.
The analysis tells us nothing about the location of the ill-fated plane. It tells us nothing about any changes in altitude that the plane flew, other than it was airborne.
Neither does it tell us about its speed or its fuel capacity at the times of those pings. All this technique really does at the moment is tell us that the plane was moving one way rather than the other.
But that in itself is a stomach-churning realisation for the families of flight MH370 because it means the plane was moving far away from any landing possibility. The only conclusion can be that it eventually ditched in the ocean.
Right 'haystack'
Chris McLaughlin, senior vice-president at Inmarsat, told BBC News it was "dealing with a totally new area". Analysts will continue to probe the available data, but it is uncertain whether anything more can be drawn out.
The UK's Air Accidents Investigation Branch (AAIB), which has worked with Inmarsat on the pings, is expected to go into more detail on Tuesday.
At least now search planes and ships know they are likely looking in the right "haystack", even if it is still a huge one.
But there is urgency. A lot of time has elapsed between the loss of the plane and confirmation that it surely fell into the southern Indian Ocean.
The priority is to get ships into the area to retrieve purported debris items, to help narrow the zone of the probable of impact.
The flight recorders from flight MH370 will be close to that location, albeit about 3,500m down.
The batteries on these "black boxes" have a 30-day, or perhaps even a 40-day, lifetime, meaning they will continue to ping their existence to searchers overhead for only a limited period.
When the batteries go flat, we move into a much more difficult phase - that of using remotely operated vehicles to actively look for the devices.
'Remoteness of area'
"The data on them should last for many years. We saw with Air France flight 449 that the black boxes were recovered two years after the fact, and the French were able to pull all the data off them," said Van Gurley from the Metron company, which took part in the search for flight 447.
"In this region of the Indian Ocean, the bottom is about two miles down. There are a number of technologies - sonar sleds and robotic vehicles - that can access that depth.
"The problem is the remoteness of the area because those robotic vehicles need a support ship and a support ship needs to occasionally go [into port] for fuel, water and food.
"So, given that the search area is 1,500 miles off Perth, just keeping ships on station for an extended period of time will be very challenging."
And Simon Boxall, an oceanographer at the University of Southampton, added: "We don't have very good maps of this region. It hasn't been surveyed much in the past.
"It doesn't have a strong interest in terms of the resources on the seabed. We've probably got better maps of the Moon's surface than this part of the seabed."
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