Low Frequency Portable Acoustic Measurement System

sensors
Low Frequency Portable Acoustic Measurement System (LAR-TOPS-13)
A system to detect and locate atmospheric clear air turbulence and severe weather
Overview
NASAs Langley Research Center has developed a system to detect and locate atmospheric clear air turbulence (CAT) by means of a ground-based infrasonic array to serve as an early warning system for aircraft. This system could augment existing systems such as pilot reports (PIREPs), airborne lidar, and airborne radar. The NASA system offers a benefit based on the fact that the existing electromagnetic methods lack targets at 30,000-40,000 ft and will not detect CAT. Because CAT and severe storms emit infrasound that propagates over vast distances through the Earths atmosphere, the Langley system offers an excellent early warning opportunity. The system has been able to detect known events - such as detection of the launch of the Space Shuttle in Florida all the way from Virginia.It also has correlated data with NOAAs PIREPs information.

The Technology
Langley has developed various technologies to enable the portable detection system, including: - 3-inch electret condenser microphone - unprecedented sensitivity of -45 dB/Hz - compact nonporous windscreen - suitable for replacing spatially demanding soaker hoses in current use - infrasonic calibrator for field use - piston phone with a test signal of 110 dB at 14Hz. - laboratory calibration apparatus - to very low frequencies - vacuum isolation vessel - sufficiently anechoic to permit measurement of background noise in microphones at frequencies down to a few Hz - mobile source for reference - a Helmholtz resonator that provides pure tone at 19 Hz The NASA system uses a three-element array in the field to locate sources of infrasound and their direction. This information has been correlated with PIREPs available in real time via the Internet, with 10 examples of good correlation.
Low Frequency Portable Acoustic Measurement System NASA system detected STS107 Columbia launch at Cape Canaveral, Fl., on June 16, 2003, from sensors at NASA Langley in Hampton, VA.
Benefits
  • Robust - hardware proven in various weather conditions, and sucessful wind screening
  • Portable - including detector array and field calibration
  • Proven - known events detected as well as correlation with pilot-reported data via PIREPs

Applications
  • Detection and location of clear air turbulence for aircraft
  • Severe weather monitoring, including tornado chasing via portable
  • infrasound array
  • Remote motion detection - microphone technology
  • Mine communications - infrasound travels through solid barriers
Technology Details

sensors
LAR-TOPS-13
LAR-17317-2 LAR-17317-1 LAR-17836-1 LAR-18863-1
Similar Results
Infrasound Sensor Technology
Infrasound Sensor Technology
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 is a highly refined microphone that is capable of detecting acoustic waves from 20 Hz down to dc, the infrasound range. The 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.
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