Hydrophones picking up the sounds

Hydrophones picking up the sounds can't determine what direction they're coming from, Fish said. Typically, a ship would tow the hydrophone back and forth over the search zone, ruling out areas without a signal and listening for when the signal is strongest, Fish said. His Bourne, Mass.-based company has been involved in several searches for aircraft under water.It may still take days to get a more precise location, he said.Klearfold plastic carton The hydrophone, which is pulled by a cable miles behind the boat, can swing back and forth with currents and can be difficult to control, he said.Many factors can interfere with the signal and make it harder to detect, Fish said. Temperature inversion layers known as thermoclines can bend or reflect sound waves. In one case, Fish's team wasn't able to hear a crashed helicopter's pinger beyond one-quarter mile because it had fallen beneath one of the craft's rotor blades.
The pinger should be detectable within about 2 nautical miles, Portale said.Sometimes, pingers become dislodged from the recorders, so undersea vehicles must photograph a wider area to locate them, Fish said.It also isn't clear how valuable the recorders will be to investigators if they are recovered, John Cox, president of Washington-based Safety Operating Systems, said in an interview.One of the boxes records four channels of sound from the cockpit on a two-hour loop. Since the plane flew for about seven hours after it turned off its planned course from Kuala Lumpur to Beijing and disappeared from radar,clear plastic tube it probably only captured the last two hours, said Cox, who teaches aviation safety and has been involved in several crash investigations."As far as the initial event goes, it's virtually impossible that it would be on the voice recorder," he said.