Underwater sound waves could point to sea-based plane crashes
In January of this year, officials in Australia called off the search for Malaysian Airlines Flight MH370, which had gone missing on March 8, 2014. While bits of debris from the plane were recovered, the entire aircraft and the presumed deceased passengers were never found. Now, a new study from Cardiff University (CU) points to a method that could have helped rescuers narrow down the search zone and may make it easier to find future downed craft, along with a host of other violent sea-based events.
When large objects like planes or meteors plunge into the ocean, they result in a sudden water-pressure change that creates sound waves known as acoustic gravity waves (AGWs). According to CU, these waves can penetrate deep into our seas reaching thousands of meters in depth while zipping along at the speed of sound. Instruments known as hydrophones, which are already deployed in certain areas of the ocean, can measure these waves, even if they are very faint.
"By using existing detectors dotted all around our oceans and listening out for signatures from these deep ocean sound waves, we've uncovered a completely novel way of locating objects impacting on the sea surface," said Usama Kadri, UC lecturer in applied mathematics. "Tracking these acoustic gravity waves opens up a huge range of possibilities, from locating falling meteorites to detecting landslides, snow slides, storm surges, tsunamis and rogue waves."
For their study, the CU researchers dropped 18 spheres on the surface of the water held in a tank. The spheres were dropped from varying heights and distances, and hydrophones beneath the surface recorded the AGWs that resulted from each drop. This gave the team a baseline against which to measure further data.
That data included the AGWs captured by hydrophones under the ocean off the west coast of Australia, where they are primarily used to listen for underwater nuclear tests by the Comprehensive Nuclear-Test-Ban Treaty Organization. By using the calculations developed from the sphere-drop experiments, the CU team was able to successfully calculate the time and location of recent earthquakes in the Indian Ocean, which can also generate AGWs.
With their method verified, the team members turned their attention to flight MH370 which, they say, was the initial impetus for the research. Sure enough, the team found two very weak signals along the probable flight path of the craft at the time it disappeared, although the researchers are quick to point out that the finding needs to be taken with caution.
"Though we've located two points around the time of MH370's disappearance from an unknown source, we cannot say with any real certainty that these have any association with the aircraft," said Davide Crivelli, UC lecturer in teaching and research. "What we do know is that the hydrophones picked up remarkably weak signals at these locations and that the signals, according to our calculations, accounted for some sort of impact in the Indian Ocean. All of this information has been passed onto the Australian Transport Safety Bureau and we anticipate that both now, and in the future, this new source of information could be used in conjunction with a whole of host of other data that is at the disposal of the authorities."
The following video from the CTBTO offers excellent insight into their particular hydrophone monitoring system.
Source: Cardiff University