Extreme Low Frequency Hydrophone

sensors
Extreme Low Frequency Hydrophone (LAR-TOPS-321)
Senses and isolates infrasound down to .0001 Hz while submerged
Overview
The Extreme low frequency infrasonic hydrophone, with the associated software, is capable of sensing down to .0001 Hz, a 4.999 Hz improvement from current similar systems. This ultra-low power consuming hydrophone also isolates and removes significant amounts of background noise, inherent to the electret type microphone not previously introduced into hydrophone applications. The uniquely robust unit design also permits for sub-freezing operations deep below the surface. The results promise to drastically alter lives and multiple industries, enabling totally new data for weather monitoring and earthquake/tsunami prediction among numerous other academic applications. It could also improve current hydrophone accuracy or reliability in finding oil resources, and will enable monitoring human generated infrasound in water.

The Technology
The extreme low frequency hydrophone boasts unprecedented capability for precise detection as proven in testing, where it sensed wave range between surface waves and tidal surges with periods between .3 and 30 seconds, or 3 to .033 Hz. The technology uses a back-electret microphone, inherently reducing noise, in a stainless steel body. The stainless steel diaphragm conducts infrasound well and the materials robust nature and internal configuration facilitates sub-freezing and deeply submerged sensing of sound down to .0001 Hz. With an appropriately spaced array of three hydrophones it is possible to determine the direction of origin of a submerged infrasonic source, the addition of one more in another location will also enable determination of the precise location of origin. The oil industry uses existing infrasound systems to locate undersea oil deposits and this technology could potentially improve the accuracy or reliability of current practices. It could also be used to give tsunami and earthquake warnings, monitor ships, and to generate electrical energy from infrasound. This technology has potential to unlock new industry uses not currently understood due to the unprecedented nature of its capabilities.
buoy Image of prototype hydrophone. Image Credit: NASA
Benefits
  • Frequency range from .0001 Hz up to 100 Hz detection range
  • Electret based design eliminates more background noise than other hydrophones
  • Can be used in high pressure marine environments
  • Can be used to detect infrasound below freezing temperatures
  • Low power consumption

Applications
  • Offshore oil industry
  • Weather monitoring (earthquake, tsunami and tidal)
  • Monitoring wind-generated gravity waves on the free surface of the bodies of water
  • Monitoring of man-made infrasonic sources such as boats
  • Piezoelectric design allows for energy harvesting from full detection range
Technology Details

sensors
LAR-TOPS-321
LAR-19681-1 LAR-19059-1
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.
Adaptive Algorithm and Software for Recognition of Ground-based, Airborne, Underground, and Underwater Low Frequency Events
Acoustical studies of atmospheric events like convective storms, shear-induced turbulence, acoustic gravity waves, microbursts, hurricanes, and clear air turbulence over the last forty-five years have established that these events are strong emitters of infrasound (sound at frequencies below 20 Hz). Over the years, NASA Langley has designed and developed a portable infrasonic detection system which can be used to make useful infrasound measurements at a location where it was not possible previously. The system comprises an electret condenser microphone, and a small, compact windscreen. The system has been modified to be used in the air, underground, as well as underwater (to determine man-made and precursor to tsunami). The system also features a data acquisition system that permits real-time detection, bearing, and signature of a low frequency source. However, to determine bearing of the received signals, the microphones are to be arranged as an equilateral triangle with a certain microphone spacing. The spacing depends upon location of the microphone array. For a ground-based array, the microphone spacing of 100 feet (30.48m) is desired to determine time delay for signals arriving at each microphone location. The microphone spacing depends upon speed of sound through the array medium. For underwater array, the spacing between microphones would be around 1500 feet. The data acquisition system provides data output in the infrasonic bandwidth which is then analyzed using an adaptive algorithm (least-mean-squares time-delay-estimation) using modern computational power to locate source by plotting source location hyperbolas on-line. A smaller array size reduces the time resolution resulting in strong signal coherence. The innovation approach is to exploit modern signal processing methods, i.e. adaptive filtering, where computer is trained on-line to recognize features of the event to be detected. Modern computational capability permits the adaptive algorithm (least-mean-squares time-delay estimation or LMSTDE) which is vastly more powerful algorithm. This system has better resolution able to determine direction with arrived signals within five-degree accuracy.
Atmospheric sound
High Altitude UAV for Monitoring Meteorological Parameters
Radiosondes are launched twice a day from different locations of the world and meteorological data is collected to plot the STUV diagram and determining CAPE (Cumulative Average Potential Energy) values. Radiosondes are not re-usable and used only at pre-determined locations around the globe. Moreover, a radiosonde can drift up to 125 miles from its release point. About 75,000 radiosondes are used every year. Given this unmet need, an inventor at NASA has developed an advanced airborne meteorological system which can provide meteorological parameters at any location at any desired time. In additional to routinely used meteorological sensors, an infrasonic sensor is also included to determine wind shear at local and regional levels. The airborne system may also be used in towns and cities to track drones and UAVs in the area. The airborne vehicle (UAV or drone) should be able to track seismic waves, magnetic storms, magneto-hydrodynamic waves, tornadoes, meteor, and lightning, etc. This technology can be use to measure environmental turbulence including wind shear, vortices as well as large and small eddies is an important factor in forecasting local and regional weather. It can also detect infrasound at ranges of many miles from the source and the shape of the acoustic power spectrum can be used to identify type of turbulence in the atmosphere.
High-Fidelity Sonic Boom Propagation Tool
The sBOOMTraj tool offers an updated approach to accurately predict sonic boom ground signatures for supersonic aircraft. The tool is based on the numeric solution of the augmented Burgers equation where the regular Burgers equation is augmented with absorption, molecular relaxation, atmospheric stratification, and ray tube spreading terms in addition to the non-linear term from the regular equation. The primary idea behind such augmenting is that atmospheric losses are captured, which results in more realistic sonic boom predictions compared to linear theory methods. While previous iterations of the software (sBOOM) were limited to single point analysis (i.e., a point in supersonic climb or cruise), sBOOMTraj extends the prediction of sonic boom to multiple points along the supersonic mission. This includes updated functionality to handle aircraft trajectories and maneuvers as well as inclusion of all relevant noise metrics. The improvements allow efficient computation of sonic boom loudness across the entire supersonic mission of the aircraft. The sBOOMTraj tool can predict ground signatures in the presence of atmospheric wind profiles, and can even handle non-standard atmospheres where users provide temperature, wind, and relative or specific humidity distributions. Furthermore, sBOOMTraj can predict off-track signatures, ground intersection location with respect to the aircraft location, the time taken for the pressure disturbance to reach the ground, lateral cut-off locations, and focus boom locations. The software has the ability to easily interface with other stand-alone tools to predict the magnitude of focus, post-focus, and evanescent booms, and also has the ability to handle different kinds of input waveforms used in design exercises. The sBoomTraj tool could be extremely useful in supersonic aircraft operations as it can predict where sonic booms hit the ground in addition to providing the magnitude of sonic boom loudness levels using physics-based simulations. Using this tool, pilots may be able to steer supersonic aircraft away from populated areas while also allowing real-time adjustments to their flight trajectories, allowing trade-offs associated with sonic boom, performance and acceptability. The predicted sonic boom loudness contours during supersonic flight may also be used in supersonic aircraft design and development, including certification of aircraft under future regulations that may be imposed. sBOOMTraj offers a revolutionary approach to mitigating sonic boom through its unique sonic boom adjoint equations. This potentially has immediate and realizable benefits in supersonic aircraft design when integrated with other disciplines. The NASA technology can potentially aid in supersonic aircraft operations with its integration in a cockpit interactive application that can provide feedback to the pilot on sonic boom impingement areas on the ground with real-time atmospheric and terrain updates. sBOOMTraj has the potential to support both aircraft design and operations, which is extremely rare.
Simulated vorticity field generated by flow past a full-scale Gulfstream aircraft in landing configuration
Application of Leading Edge Serration and Trailing Edge Foam for Undercarriage Wheel Cavity Noise Reduction
Among the tests, landing gear cavities, a known cause of airframe noise, were evaluated. These are the regions where the landing gear deploys from the main body of an aircraft, typically leaving a large cavity where airflow can get pulled in, creating noise. NASA applied two concepts to these sections, including a series of chevrons placed near the front of the cavity with a sound-absorbing foam at the trailing wall, as well as a net that stretched across the opening of the main landing gear cavity. This altered the airflow and reduced the noise resulting from the interactions between the air, the cavity walls, and its edges.
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