NASA Langley Research Center scientists have developed a microphone that detects infrasound, i.e., acoustic waves ranging from 20-Hz frequencies down to DC. Infrasound is emitted in a number of hazardous atmospheric phenomena, including aircraft wake vortices, clear air turbulence, and tornadoes. It is also emitted by seismic events such as underground nuclear tests, digging of tunnels, etc. Infrasound propagates hundreds of miles and can penetrate walls, mountains, and other obstacles without loss.
The NASA infrasound sensor filters out wind noise that can interfere with detection, while using less power and much less space than currently available solutions. As a result, the NASA infrasound sensor can detect tornadoes and clear air turbulence hundreds of miles away; an array of 30 could cover the entire continental U.S. Aircraft wake vortices can be detected in real time by microphone arrays placed along an airport runway.
Large aircraft can generate air vortices in their wake — turbulence that can prove hazardous to aircraft that follow too closely. Because wake vortices are invisible, all takeoffs at busy airports are spaced several minutes apart. This separation gives the vortices time to dissipate, even though they only occur 10% of the time, with resulting loss of operational efficiency. Similarly, clear air turbulence is invisible and can also be hazardous to aircraft. By detecting such disturbances through their infrasound emissions, precautions can be taken to avoid them.
Other phenomena can be detected through infrasound, including tornadoes, helicopters on the other side of mountains, underground nuclear explosions, and digging tunnels. Through the unique properties of infrasound, many of these can be detected from hundreds of miles away.
NASA’s infrasound sensor design is robust and compact, eliminating the bulk and weight found in other technologies. Where most alternative methods are restricted to certain weather conditions and locations, the NASA sensor filters noise from wind and other sources, allowing its use under any weather or geographic conditions.