The cluster of suspected debris from Malaysia Airlines flight MH370 has been sighted above a giant undersea chain of volcanoes whose complex terrain has barely been charted, an Australian marine geologist says.
MH370 search area still to be defined
"We're not searching for a needle in a haystack, we're still trying to define where the haystack is," cautions Vice Chief of the Defence Forces Mark Binskin at the RAAF base Pearce near Perth on Tuesday afternoon.
Robin Beaman, from James Cook University, said so little of the southern Indian Ocean sea floor, including the search zone, had been mapped in detail that any attempt to retrieve wreckage would require extensive 3D mapping, possibly by ships with multibeam echo sounders.
But Australia no longer has the capacity to chart depths of 3000 metres, the average depth of the search area, because the only government vessel capable of conducting mapping of that kind, the RV Southern Surveyor, had been decommissioned in December.
The research vessel's replacement was being built in Singapore and was about to undergo sea trials, Dr Beaman said.
''It's bad timing really. Australia has no capability of mapping these depths,'' he said. Multibeam echo sounders send out sound pulses in the shape of a fan, returning depths of the sea floor directly under the ship and on either side, a pattern known as a swath.
Dr Beaman said the first piece of debris spotted by DigitalGlobe satellites on March 16 was located about 60 kilometres south-west of the active zone of the Southeast Indian Ridge, a chain of underwater volcanoes that ran from the south-west of Australia to below New Zealand. Another object sighted by a Chinese aircraft was about 180 kilometres south-west of the ridge.
The suspected debris picked up by an Australian aircraft on Monday was spotted about 200 kilometres to the north-east of the ridge, Dr Beaman said.
''On the flanks of the ridge, which is very likely where any crash zone occurred, there has been virtually no … mapping apart from the odd strip,'' he said.
The complex terrain of the ridgeline, with peaks tens of metres tall, would make it difficult to spot any debris without good charts and remote-operated underwater vessels.
''It's all going to have to be remapped, there's no doubt,'' he said.
International research groups had conducted sea floor surveys in the region, using multibeam echo sounders to create 3D maps of the sea floor, but the last two surveys occurred almost 20 years ago and used outdated technology, he said.
These surveys charted several areas about 70 kilometres wide while other research ships had gathered detail on the sea floor as they sailed from one port to another, but the paths they charted were only about 10 kilometres to 20 kilometres wide.
''It'll be very unlikely that debris has fallen in those little 10 to 20-kilometre wide zones,'' he said.
''You're left with gaps of hundreds of kilometres where there is no detailed understanding of what the sea floor terrain looks like.''
Dr Beaman said it was not surprising that an area of deep open water so far from land or regular shipping routes had not been charted in detail. ''You have to put your effort where it's most needed,'' he said. ''There's very little to bump into and the search zone is 2000 kilometres from the edge of our exclusive economic zone.'' Only depth readings were available for most of the search area.
A Defence spokeswoman said while the search area was within the Australian Hydrographic Service's area of charting responsibility, it had not been mapped to great detail because of the very deep nature of the region, which made it less risky for ships.