Wind Noise Reduction Research Articles

In-situ calibration for real-time infrasound station monitoring and improved wave parameter determination

Infrasound signals can be detected using a time-delay of arrival approach to derive the back azimuth and trace velocity of the coherent wave. For these calculations, it is necessary to have a calibrated measure of the pressure. Although the calibration of microbarometers can be performed in a laboratory setting and in the field with specific metrological means such as those developed by the CEA, it is much more difficult to determine the transfer function of the wind noise reduction systems (WNRS), designed to reduce the wind associated noise. In-situ calibration of these WNRS's can be performed using a co-located, calibrated reference sensor. System defects, such as flooded pipes or blocked inlets, have significant impacts on the response, which in turn would influence the calculated infrasonic wave parameters. These defects can be characterized using in-situ calibration measurements. Experiments were undertaken at the infrasound station IS26 as part of the EMPIR Infra-AUV project, using a temporary detector that was used to simulate defects on the WNRS. This allowed for the effects on real infrasound detections to be quantified and corrected using in-situ calibrations. Additionally, case studies at IMS stations were performed demonstrating the utility of these methods on operational infrasound stations.

Wind Noise Reduction Strategy in Hearing Aids Through U-Net Deep Learning and Microphone Enclosure Design

Wind Noise Reduction Strategy in Hearing Aids Through U-Net Deep Learning and Microphone Enclosure Design

Towards a rapid-distortion theory model of turbulent flow for wind noise within an impermeable windscreen

Current models for the wind noise reduction (WNR) of microphone windscreens in atmospheric turbulence generally work under the assumption of a homogeneous surface pressure averaging theorem. Under this theorem, the surface pressures should average in such a way that the noise spectrum at low wavenumbers relative to the windscreen dimension should approach that of an unscreened microphone. Contrasting this, experiments have actually observed a significant WNR at these wavenumbers. In this work, we examine a Rapid Distortion Theory model for linking turbulent distortion to the unsteady pressure received inside the windscreen. The theoretical background and underlying assumptions of Rapid Distortion Theory are examined in detail [R. Zamponi, et al., J. Fluid Mech. 915:A27 (2021)], then results for the case of an impermeable cylinder are presented. Future work on the project involving both theoretical development and experimental verification are then discussed.

Dealing with wind noise on resource constrained acoustic sensors

Single and multiple microphones in small or hand-held devices, i.e., mobile phones, are often single port and without windscreens. In a typical outdoor situation, this configuration can be subject to strong impulsive wind noise events and wind-induced tones. Smart mobile phones can sometimes utilize their significant computational power to employ sophisticated signal processing to reduce or remove wind-associated noise. However, in systems where battery conservation is paramount and computational processing resources are severely limited, alternative strategies must be employed. This presentation will discuss exemplar wind noise data from a single channel, resource-constrained system, methods for wind noise reduction, and results.

Development of a weather robust microphone configuration for sonic boom measurments

This paper discusses ongoing development and testing of ground-based, weather-robust microphone measurement systems in conjunction with preparation for community testing of NASA's X-59 low-boom aircraft. Prior efforts [Anderson et al., Proc. Mtgs. Acoust. 42, 040005 (2022)] resulted in the refinement of a ground-plate setup by investigating varied windscreen and plate diameter and thickness. The most recent goal has been to make the setup more compact and easier to manufacture. This paper discusses the results of additional tests performed on updated designs meant to find the balance between compactness and performance. Anechoic chamber testing was performed to show ground plate and windscreen performance and to compared results against prior versions. Outdoor tests included measurements during different wind conditions and over different ground surfaces to examine low-frequency wind noise reduction and ground impedance effects. Results discussed during the presentation suggest the new design strikes an acceptable compromise between compactness, manufacturing ease and robustness, and performance. [Work supported by NASA Langley Research Center through Analytical Mechanics Associates]

The use of in situ infrasound calibration to correct wave parameter estimation

As part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), the International Monitoring System (IMS), which includes infrasound stations, has been established to monitor nuclear testing, as well as many other infrasound sources of interest to the scientific community. To minimize the effects of wind-noise, wind-noise reduction systems (WNRS) are installed as part of each sensor. In order to provide the best wave parameter (azimuth, trace velocity, amplitude) estimates, the response of the WNRS must be properly taken into account. Therefore, it is important to perform an in-situ calibration of the sensor using a co-located reference sensors and ambient signals to determine this response. This in-situ calibration can be used to monitor the status of the sensors, and provide feedback to the station operators. Experiments were performed at the IS26 site in Germany using a temporary WNRS to provide quantitative measurements of the effects of the WNRS and its calibration on the wave parameter estimation. These calibration results were used to provide corrections to the raw signal data for retrieval of the corrected wave parameters and were compared to the IS26 measurements, demonstrating that accurate measurements can be retrieved using the in-situ calibration.

On-site infrasound calibration to correct wave parameter estimation.

The International Monitoring System (IMS) has been established as part of the Comprehensive Nuclear-Test-Ban Treaty to monitor nuclear testing and is comprised of infrasound, hydroacoustic, seismic, and radionuclide stations; it is also used more widely by the scientific community for scientific and civilian applications. For the infrasound stations, on-site calibration provides an accurate measure of the sensor (microbarometer + wind-noise reduction system) frequency response, used to monitor that the sensor response remains within tolerance of the baseline established when the station is certified. However, this on-site calibration can also be used when there are issues/defects with the sensors. As a result, the on-site calibration can be used to correct wave parameter estimations and increase the detection capability of the station. Examples using an experimental sensor at the IMS station IS26 (Germany) and IS47 (South Africa) demonstrate that errors of several degrees and tens of m/s can be introduced, under certain conditions, for the back azimuth and trace velocity, respectively. By using the on-site calibration, these errors are removed, and the correct back azimuth, trace velocity and amplitude are retrieved. This can be especially useful for the identification of infrasound signals, and the localization of their sources.

Multidisciplinary design of door inner belt weatherstrip for simultaneous reduction of wind noise and squeaking in electric vehicles

In electric vehicles (EVs), addressing noise, vibration, and harshness (NVH) has become pivotal, especially concerning external wind noise. To reduce wind noise, a door inner belt weatherstrip needs a high contact load, but this can lead to squeaking noise at the glass/weatherstrip interface. This study demonstrates a multidisciplinary design for the weatherstrip to tackle both issues. By increasing ethylene propylene diene monomer and ethylidene norbornene contents in the thermoplastic vulcanizate (TPV) by about 20 % and 70 %, respectively, the compression set was reduced from 35.4 % to 27.6 %. Concurrently, the TPV’s damping properties improved, with a 25 % increase in loss modulus (323 MPa). Coated flocking surface of weatherstrip significantly reduced the friction coefficient by 80 % (from 1.75 to 0.30). In vehicle evaluations, the newly designed weatherstrip reduced the wind noise by 5 dB(A) and eliminated. This approach highlights the potential of multidisciplinary design in optimizing NVH for next-generation vehicles, including autonomous EVs and urban air mobility.

Snow Attenuation of Infrasound Signals and Wind Noise

Abstract Infrasound monitoring of geophysical and human-sourced activity, such as explosions, eruptions, earthquakes, and avalanches, may be impacted by burial of sensors in a snowpack. We studied the frequency-dependent attenuation of sound, vertical sound speed, and wind noise reduction in a natural snowpack using earthquakes as a natural source of infrasound. Our experiment used a 2 m vertical distribution of sensors deployed during the 2021–2022 winter in the Sawtooth mountains of Idaho. We recorded 38 earthquakes and their primary infrasound propagating vertically upward through the snow. For these events, average attenuation appeared negligible between 0 and 8 Hz, rose to 0.1 dB/cm at ∼12 Hz, and remained at this level for higher frequencies. Using timing lags across the vertical profile the speed of infrasound in the snow was measured at 160 ± 51 m/s, significantly subsonic and indicative of pore-space waves. Finally, we quantified the significant reduction in the amount of background noise measured for snow-buried compared with free-air sensors. The 24 dB of reduction of noise observed for high wind speed conditions was evident with only 20 cm of snow burial and demonstrates the powerful capability of snowpack as a noise reduction filter. This study provides a clearer understanding of how snow burial filters infrasound and minimizes noise levels and has implications for monitoring of both natural and human-made hazards.

Contribution to Uncertainty Propagation Associated with On-Site Calibration of Infrasound Monitoring Systems

To improve the confidence and quality of measurements produced by regional and international infrasound monitoring networks, this work investigates a methodology for propagating uncertainty associated with on-site measurement systems. We focus on the propagation of sensor calibration uncertainties. The proposed approach is applied to synthetic infrasound signals with known back azimuth and trace velocity, recorded at the array elements. Relevant input uncertainties are investigated for propagation targeting the incoming signals (noise), instrumentation (microbarometers, calibration system, wind noise reduction system), and the time-delay-of-arrival (TDOA) model (frequency band). Uncertainty propagation is performed using the Monte Carlo method to obtain the corresponding uncertainties of the relevant output quantities of interest, namely back azimuth and trace velocity. The results indicate that, at high frequencies, large sensor uncertainties are acceptable. However, at low frequencies (<0.1 Hz), even a 2∘ sensor phase uncertainty can lead to errors in the back azimuth of up to 5∘ and errors in the trace velocity of 20 m/s.

Infrasound noise mitigation on high altitude balloons

Wind noise significantly limits the use of infrasound for remote sensing using ground-based sensors. Recently, there has been a surge in studies using high altitude balloons, termed heliotropes, to mitigate this problem. Since the balloon drifts with the wind there is minimal relative speed between the balloon and the local air. To resolve the direction of arrival from a signal, there must be sufficient separation between sensors. However, this separation increases the relative motion between the sensors and the local air. On Earth this has shown to have a weak dependence, but the use of such measurements are currently being considered as a means of exploring the interior of Venus. Vertical shear on Venus is between 5 and 10 m/s per km, which will create approximately 1 m/s of relative wind speed per 100 m of separation. Thus, the current work aims to identify wind noise reduction schemes for balloon based infrasound sensing on Venus using an Earth analog. This presentation will report on a variety of windscreen configurations examined, ground-based testing of the designs, and heliotrope flight testing of windscreens.

Infrasound single-channel noise reduction: application to detection and localization of explosive volcanism in Alaska using backprojection and array processing

SUMMARY Infrasound sensors are deployed in a variety of spatial configurations and scales for geophysical monitoring, including networks of single sensors and networks of multisensor infrasound arrays. Infrasound signal detection strategies exploiting these data commonly make use of intersensor correlation and coherence (array processing, multichannel correlation); network-based tracking of signal features (e.g. reverse time migration); or a combination of these such as backazimuth cross-bearings for multiple arrays. Single-sensor trace-based denoising techniques offer significant potential to improve all of these various infrasound data processing strategies, but have not previously been investigated in detail. Single-sensor denoising represents a pre-processing step that could reduce the effects of ambient infrasound and wind noise in infrasound signal association and location workflows. We systematically investigate the utility of a range of single-sensor denoising methods for infrasound data processing, including noise gating, non-negative matrix factorization, and data-adaptive Wiener filtering. For the data testbed, we use the relatively dense regional infrasound network in Alaska, which records a high rate of volcanic eruptions with signals varying in power, duration, and waveform and spectral character. We primarily use data from the 2016–2017 Bogoslof volcanic eruption, which included multiple explosions, and synthetics. The Bogoslof volcanic sequence provides an opportunity to investigate regional infrasound detection, association, and location for a set of real sources with varying source spectra subject to anisotropic atmospheric propagation and varying noise levels (both incoherent wind noise and coherent ambient infrasound, primarily microbaroms). We illustrate the advantages and disadvantages of the different denoising methods in categories such as event detection, waveform distortion, the need for manual data labelling, and computational cost. For all approaches, denoising generally performs better for signals with higher signal-to-noise ratios and with less spectral and temporal overlap between signals and noise. Microbaroms are the most globally pervasive and repetitive coherent ambient infrasound noise source, with such noise often referred to as clutter or interference. We find that denoising offers significant potential for microbarom clutter reduction. Single-channel denoising of microbaroms prior to standard array processing enhances both the quantity and bandwidth of detectable volcanic events. We find that reduction of incoherent wind noise is more challenging using the denoising methods we investigate; thus, station hardware (wind noise reduction systems) and site selection remain critical and cannot be replaced by currently available digital denoising methodologies. Overall, we find that adding single-channel denoising as a component in the processing workflow can benefit a variety of infrasound signal detection, association, and location schemes. The denoising methods can also isolate the noise itself, with utility in statistically characterizing ambient infrasound noise.

Wind-noise reduction for infrasonic measurements using adaptive line enhancement.

Measurement quality and analysis capability of infrasonic signals are both affected by background wind-noise. Physical filters, i.e., barriers and pipe arrays, are traditionally employed to reduce such noise. However, limited efficacy, site dependence, cost, requirement of space, non-portability, and frequent maintenance are some of their major drawbacks. This work proposes an adaptive filtering-based adaptive line enhancer (ALE) noise cancellation scheme as an alternative. Two infrasonic sensors (Chaparral Physics 50A), are adjacently deployed. One sensor is fitted with a conventional four-armed non-porous hose array (physical filter), while the ALE scheme is applied to the second sensor, sans physical filter. In high wind-noise conditions, the ALE scheme seems to behave as a lowpass filter (cutoff at 0.2 Hz), with a maximum attenuation of 26 dB at 8 Hz, while the physical filter provides significant attenuation only above 4 Hz with a maximum attenuation of 17 dB at 8 Hz. Generally, at other frequencies, the ALE scheme provides up to 20 dB superior noise attenuation as compared to the physical filter. The ALE also provides up to 6 dB gain in the signal-to-noise ratio as compared to the physical filter, due to non-attenuation of the infrasonic signal.

Wind Tunnel Study on Aerodynamic Characteristics of the Train on Viaducts with a New Type of Wind–Noise Barrier Under Cross Wind

Traditional noise barriers are often designed only by considering its noise reduction effects, but designer ignores that it may transfer too much aerodynamic force to the bridge. In order to meet the wind resistance and noise reduction requirements of the elevated lines crossing an urban area at the same time, a new type of wind–noise barrier (NT-WNB) is proposed. The noise reduction effect is evaluated by a numerical method, and the influence of the wind–noise barriers’ rotation angle on the aerodynamic characteristics of a train–bridge system was studied by sectional model wind tunnel tests. The results show that the NT-WNB has effective noise reduction in the frequency range of 500–1600 Hz, and the noise reduction can be increased when install barriers with upward incline blade. Although an angle combination type of wind–noise barrier can optimize the lateral force and the lift of the train at the same time, which may cause high turbulence in the corresponding area. The NT-WNB can reduce the wind load of the bridge–barrier system by 22%, which is more conducive to the safety of the bridge and the barrier.

Noise reduction in infrasound signals based on mask coefficient binary weighting – Generalized cross correlation – Non-negative matrix factorization algorithm

Infrasound noise reduction has two difficulties: the extremely limited datasets and the overlap of frequency bands. To overcome these problems, we present an algorithm, named MCWGCC-NMF, for noise reduction in multi-sensor recordings of mixture infrasound signals. The method is based on non-negative matrix factorization (NMF), and it is combined with spatial information estimated by generalized cross correlation (GCC) and mask coefficient binary weighting (MCW). The source dictionary masking by GCC-NMF, which uses spatial information of individual NMF atoms, is performed by frequency weighting and threshold selection to alleviate the frequency overlap. The results show that the proposed method achieves consistently better performance than the GCC-NMF on the infrasound dataset. Our study provides a signal processing method of infrasound noise reduction, which has the potential to further enhance the signals reception of infrasound arrays with wind noise reduction system (WNRS).

Large porous wind barriers as a mitigation technique for turbulence induced infrasonic noise

An infrasonic wind barrier is a large porous device that effectively reduces wind noise by disrupting and minimizing the flow near the pressure sensor, and transferring the local and direct turbulence induced noise interactions from the pressure sensor to the surface of the barrier where the sum total of the poorly correlated noise induced turbulence interactions are reduced by area averaging. In addition to effective wind noise reduction these devices maintain acoustic waveform fidelity, work in adverse conditions, and can reduce noise frequencies with associated turbulence scales sizes that are several times the size of the barrier itself. This paper will review wind barrier research conducted at the National Center for Physical. This will include a discussion on the mechanical properties of the barrier that lead to effective noise reduction including its porosity, size, shape, and number of filtering layers. Barriers designed and studied at the National Center for Physical Acoustics and by others are compared and discussed. A simple empirical model predicting wind noise reduction based on the mechanical properties of the barrier and the turbulence flow interactions located inside, on the surface, and outside of the barrier is given

Application of spectral-based wind noise reduction method to acoustical measurements

Wind-induced microphone self-noise is a non-acoustic signal that may contaminate outdoor acoustical measurements, particularly at low frequencies, even when using a windscreen. A recently developed method [Cook etal., JASA Express Lett. 1, 063602 (2021)] uses the characteristic spectral slope of wind noise in the inertial subrange for screened microphones to automatically classify and reduce wind noise in acoustical measurements in the lower to middling frequency range of human hearing. To explore its uses and limitations, this method is applied to multiple acoustical measurements collected in both urban and rural environments. The method can be applied to one-third octave band spectral data with different frequency ranges and sampling intervals. By removing the shorter timescale data at frequencies where wind noise dominates the signal, the longer timescale acoustical environment can be more accurately represented. While considerations should be made about the specific applicability of the method to particular datasets, the wind reduction method allows for simple classification and reduction of wind-noise-contaminated data in large, diverse datasets. [Work supported by U.S. Army SBIR.]

Update on using metal domes for wind noise reduction at infrasonic frequencies

The utility of infrasound for long range monitoring applications such as remote chemical explosions, or natural sources of infrasound such as tornadoes, volcanoes or hurricanes, continues to be hampered by the high noise floors experienced in the presence of high winds. Wind noise is typically filtered using pipe arrays. But these generate significant distortion, making them non-ideal for signals with significant frequency content above a few Hz, and do not produce sufficient noise reduction during windy measurements even at their optimal frequency band (0.5–1 Hz), making their utility generally limited to low-wind-noise periods. We present here an update on resesarch performed by the National Center for Physical Acoustics (NCPA) using field sites near Oxford (University of Mississippi Field Staiton) and at the Sandia National Laboratory Facility for Acceptance, Calibration, and Testing (FACT) site. The 20-foot dome at the FACT site is collocated with an IMS 18-m rosette filter and a wind noise filter developed by the University of Alaska Fairbanks. We compare in this presentation the relative performance of traditional pipe arrays to the 20-ft dome. The performance of smaller wind domes, including 42-in.2 perferorated metal domes developed at the NCPA, are also discussed.

Initial performance analysis of an array of low-cost infrasound sensors with 43 elements

Many infrasound sensor arrays are limited in the number of elements because of the cost of individual sensors. While some of these sensors are of exceptional quality and have calibrated (amplitude and phase) response to frequencies below 0.01 Hz, not all infrasound sensing applications require this degree of accuracy and precision. Moreover, to achieve significant reduction of the influence of wind noise at infrasound frequencies below 1 Hz requires large and/or complex mechanical wind screen apparatus. There are applications for which the benefits of having a so-called “large-N” array of lower cost, lower performance sensors outweigh the benefits of very high performance sensors. These benefits include wind noise reduction without large windscreens and the ability to resolve several acoustic sources simultaneously. This presentation will present preliminary array processing performance results from the deployment of an array of 43 recently developed, experimental low-cost infrasound sensors.

An experimentalist's overview of wind reduction systems in infrasound measurements

The largest limiting factor in infrasound measurements is wind noise. This noise is caused by pressure fluctuations generated by turbulent flow passing over an acoustic sensor. The size scales of these turbulent fluctuations vary from centimeters to tens of meters and larger. This, coupled with the wide variety of possible measurements, means that there is no single best solution to this problem. Instead, wind reduction systems should be tailored to best fit the intended measurement. In this talk, I will give a brief review of wind noise from an experimentalist’s point of view, and will discuss some of the physical principles to consider when choosing a wind noise reduction system. This will include spherical and domed wind screens, porous hoses and pipe arrays, probe microphones, and terrain and foliage considerations.