US Navy explains process of detecting deep-sea acoustic signals

A statement from a spokesman for the US Navy's 7th Fleet Commander, has revealed the process of how the signal was detected by the Australian navy vessel Ocean Shield which is using black-box detection equipment provided by the US Navy.  [Special coverage]

The statement said that two separate signal detections occurred within the northern part of the defined search area. The first signal was detected Sunday. The detection equipment, known as a pinger locator, was at about 300 meters below sea water.

To avoid confusion, Ocean Shield then turned off all equipment that can produce sound. It lowered the pinger locator to 1400 meters below sea water. The first detection was held for over 2 hours.

The ship then lost contact before turning around and attempting to reacquire the signal. Five hours later, another detection was made it lasted about 15 minutes when the pinger locator was about 3000 meters below water. Both signals were not detected in Monday's search. The frequency of the two detections were at 33.3 kilohertz which is different from the normal frequency of black boxes, which is 37.5 kilohertz.

A US Navy technician who helps to run the pinger locator and the underwater vehicle, said that the exhausting battery of the black box might be a reason why the signal was not stable.