Technique used to analyze plane's faint pings

The British company Inmarsat used a wave phenomenon discovered in the 19th century to analyze the seven pings its satellite picked up from Malaysia Airlines Flight MH370 to determine its final destination.

The new findings led Malaysian Prime Minister Najib Razak to conclude on Monday that the Boeing 777, which disappeared more than two weeks ago, crashed thousands of miles away in the southern Indian Ocean, killing all 239 people on board.

The pings, automatically transmitted every hour from the aircraft after the rest of its communications systems had stopped, indicated it continued flying for hours after it disappeared from its flight path from Kuala Lumpur to Beijing.

From the time the signals took to reach the satellite and the angle of elevation, Inmarsat was able to provide two arcs, one north and one south, that the aircraft could have taken.

Inmarsat's scientists then analyzed the faint pings using a technique based on the Doppler effect, which describes how a wave changes frequency as the distance varies between it and an observer, in this case the satellite, a spokesman said.

The Doppler effect is why the pitch of a police car siren gets higher as it approaches and lower as it moves away from an observer.

Britain's Air Accidents Investigation Branch was also involved in the analysis.

"We then took the data we had from the aircraft and plotted it against the two tracks, and it came out as following the southern track," said Jonathan Sinnatt, head of corporate communications at Inmarsat.

The company then compared its theoretical flight path with data received from Boeing 777s it knew had flown the same route, he said, and it matched exactly.

The findings were passed to another satellite company to check, he said, before being released to investigators on Monday.

The paucity of data - only faint pings received by a single satellite every hour or so - meant techniques like triangulation using a number of satellites or GPS could not be used to determine the aircraft's flight path.

Stephen Wood, CEO of All Source Analysis, a satellite analytics firm, said it seemed that the investigators had narrowed down the area substantially. "But it's still a big area that they have to search," he said.

"This type of incident will cause everyone who flies airplanes commercially with passengers to be really pressed for a whole new line of ways to keep track of their precious cargo," said Wood, a former US intelligence officer who headed the analysis unit of DigitalGlobe Inc, a satellite imagery firm, until July 2013.

DigitalGlobe last week provided images that Malaysia's government called a "credible lead" for the massive multinational effort to locate the plane.

As days passed, more images and data became available, helping focus the search. But piecing that information together is time-consuming, said John Goglia, a former member of the US National Transportation Safety Board.