NASA and the aviation defence group Northrup Grumman have discovered a technique to reduce that most intrusive form of noise pollution, the "sonic boom".

Modifications on the aircraft used to test the procedure produced a marked reduction in the sonic blast and ensuing shock wave, demonstrated on a test flight on 27 August, said the partners in the seven million dollar project.

"This demonstration is the culmination of 40 years of work by visionary engineers," said Richard Wlezien, program manager for vehicle systems in NASA's Office of Aerospace Technology in Washington.

A plane flying through the atmosphere continuously produces waves similar to those created by the bow of a ship in water.

NASA

"They foresaw a way to solve the sonic boom problem, and to enable a generation of supersonic aircraft that do not disturb people on the ground. It is but one of the many frontiers in aeronautics that remain to be explored."

Shock waves

A plane flying through the atmosphere continuously produces waves similar to those created by the bow of a ship in water, NASA said in a statement.

When the plane exceeds the speed of sound - about 1200 km per hour at sea level - the pressure waves merge to form shock waves, a sonic boom usually heard as an explosion or loud rifle shot when it reaches the ground.

For the trials, Northrop Grumman modified an F-5E navy combat jet with a specially shaped "nose glove," and added aluminum substructure and a composite skin to the underside of the fuselage.

The results showed a sonic boom appreciably reduced in intensity from that of a similar unmodified plane, said NASA.