Bluefin’s AUVs have been used in the search for Malaysia Airlines flight MH370, which disappeared on 8 March 2014 with 239 people on board. They also helped Microsoft executive Paul Allen find a lost WWII battleship. O’Halloran, speaking on the phone, says that publicity like this has added to growing awareness of advanced search and salvage technology.

“People are more cognisant now that technologies exist which allow you to recover things that were once thought lost forever,” he says.

Lost at sea?

Bluefin’s AUVs are all the more impressive when you realise that they have to operate with an astonishing degree of independence and reliability. Not only are they not physically linked back to the boat that launches them; when “flying” in deep water they may lose GPS signal too, and they may suffer an extremely slow data connection back to the operators. In other words, once the AUV is launched, you want to be pretty sure it knows what it’s doing. One strategy to overcome these problems is to judge the water currents and changes in buoyancy to detect when they go off track to make sure they never wander from the region they are meant to be probing. Besides sonar, the drones can also take pictures of the sea floor and objects on it, explains O’Halloran. “The vehicles do carry cameras on them and they take pictures in the way a spy satellite would,” he says.

An underwater robot is great for getting closer to a wreck you know is in the area. But how do you go about surveying large plots of the underwater environment in the first place? Many explorers are looking for wrecks down there that no-one had previously recognised before.

One surprising approach investigated lately involves sensing from a very great distance indeed – space. Dr Rory Quinn at the University of Ulster and colleagues described how satellite imagery can detect the presence of shipwrecks underwater.

The team showed that visible light and near-infrared scanning of coastal waters allowed for the detection of plumes – clouds of sediment for example – surrounding shipwrecks. “Although satellite data cannot match acoustic and laser data in terms of resolution, it does offer the user a much broader view of the coastal landscape,” the paper notes.

Quinn points out, however, that one limitation of this type of scanning is that it is limited to coastal depths of 500 ft (150 m) or less.