Ambient Noise Monitoring Research Articles

Transient seismic velocity variation accompanying an ML 4.2 earthquake on SE margin of the Tibetan Plateau and its implication for fault slip processes

On 8 July 2020, an ML 4.2 earthquake occurred in the Xiaojiang fault zone along the eastern margin of the Tibetan Plateau. Applied ambient noise monitoring technique to the continuous waveforms from a near-fault small-aperture array, we obtain daily high-resolution variations in seismic velocity before and after the earthquake. When compared with environmental observations, we exclude these factors such as groundwater level, precipitation, temperature, and atmospheric pressure that might significantly influence the seismic velocity changes. We propose that the observed ∼10-day transitional phase from relatively high velocity to low velocity following the ML 4.2 earthquake, signifies a transition within the fault zone from a relatively compressional state to an extensional one. This transition could be an indicator of transient dilatation deformation during the long-term strike-slip process of the Xiaojiang fault, which is not easily detected by space geodetic measurements. When the fault zone is in extensional state, there is stronger strain-velocity sensitivity, which is verified by local long-period tidal strain.

The impact of marine traffic radiated underwater noise on the in the Baltic Sea

Continuous anthropogenic noise, generated by commercial shipping, is considered to exert a considerable pressure on the marine environment. Noise emitted by ships is mainly due to their propellers whose energy is predominantly at low frequencies and can interfere with the communication of marine animals. The EU Marine Strategy Framework Directive (MSFD), has set the objective of achieving good environmental status of Europe's seas. In particular, anthropogenic underwater sound should be at a level that does not harm the marine environment. Here we present the first implementation of the new framework for assessing the environmental status of low frequency continuous noise on a basin scale, carried out in the frames of the EU-funded HELCOM BLUES project. The assessment was based on modeled levels in two 125 and 500 Hz decidecade bands deemed relevant for the indicator fish and marine mammals respectively. Sound propagation modelling, calibrated against underwater ambient noise monitoring data, results in statistical sound maps in species-specific frequency bands. The application of spatial thresholds allows the environmental status of marine areas to be determined. Factors affecting the reliability of results are discussed.

Refocusing aquatic noise: Shifting from single to combined anthropogenic pressures

Aquatic animals (invertebrates, fishes, and marine mammals) are encountering an increasing array of underwater anthropogenic noises that can disrupt and even harm ecosystems as well as the lives of individuals and populations. Sources of anthropogenic noise include, but are not limited to, shipping, offshore exploration and production for fossil fuels, and the construction and operation of wind farms. Because of the continuing increase in anthropogenic noise, research on its potential effects on aquatic animals has intensified over the past two decades. However, a major under-explored issue is that noise is only one type of anthropogenic pressure acting (often simultaneously) on animals. Indeed, multiple simultaneous anthropogenic pressures are likely to affect how aquatic animals respond to each of the individual stimuli. Moreover, animal responses may be very different in the presence of multiple pressures as compared to when there is only a single anthropogenic source. We suggest refocusing of aquatic noise so that research prioritizes studies that deal with the interaction of noise with other anthropogenic pressures on aquatic life. At the same time, we call for an acceleration of studies providing baseline data for cumulative risk studies, such as monitoring of ambient noise around the globe.

High-resolution spatial elastic wave velocity variation detected using multiple-linear-array microtremor measurements

We propose a method for capturing the near-surface elastic wave velocity variation using microtremors. The proposed method does not directly estimate the velocity of the medium; instead, it measures the spatial velocity change. We apply the stretching method, which is often used to detect the time variation of shear wave velocity based on the monitoring of seismic ambient noise, to microtremor recordings. Because spatially dense ambient noise records are unavailable, we performed microtremor measurements using multiple linear arrays with multiple sensors along the survey line to collect as many recordings as possible. The synchronised microtremor recordings of each array were used to compute the horizontal-to-vertical spectral ratio (H/V), cross-correlation (CC), autocorrelation (AC), and single-station cross-correlation (SC). The H/V ratio and the waveforms of these correlation functions showed significant spatial variation. The velocity variation was measured quantitatively using the stretching method, which correlates a compressed and stretched reference function with each function on the line. The velocity variation of the vertical and radial components of CC compares well with the variation of the H/V peak, indicating that the radial components of CC retrieved the Rayleigh-wave Green’s function. The waveforms of AC and SC also showed spatial variation but the measured value of velocity change was smaller than that for CC. Further investigation is awaited to conclude if this is due to low-quality data or inappropriate measurement conditions. The reliability of the velocity change was confirmed by comparing the results to dispersion curves obtained using the conventional array method.

The effects of anthropogenic noise on frogs housed on exhibit at a public aquarium.

Anuran behavior and reproduction are dominated by vocalizations, rendering them vulnerable to the effects of signal masking. For anurans on display in zoos and aquaria, a major source of ambient noise is visitors, which pose a unique source of potential anthropogenic signal masking. Call characteristics (total call duration, and minimum and maximum call frequencies) of three populations of dendrobatids (Dendrobates leucomelas, Epipedobates tricolor, and Ranitomeya imitator) on public display were investigated at time periods of increasing visitor-related noise (closed, off-peak, and peak aquarium visiting hours) to determine if there were changes in call characteristics that correlated with changes in visitor noise levels. The data revealed that call length increased with more visitor noise for D. leucomelas and E. tricolor, with their longest calls during peak hours, and all three species had their shortest calls during closed hours. Both minimum and maximum call frequencies increased with more visitor noise for E. tricolor and R. imitator, with their highest frequencies during peak hours, and lowest frequencies during closed hours. This study found evidence that anurans on public display adjust their vocalizations in the presence of visitor noise. These findings support expanded monitoring of ambient noise for animals on public display to determine if noise poses significant effects that might influence well-being or reproduction.

Ambient Noise Monitoring and HSE Risk Mitigation by the Deployment of IoT Technology on Land Seismic Crews

Ambient Noise Monitoring and HSE Risk Mitigation by the Deployment of IoT Technology on Land Seismic Crews

Subdaily Ambient Noise Monitoring at Parkfield, California, by Combining C1 and C3

Abstract Monitoring the temporal variation in seismic velocity plays a critical role in understanding the dynamic processes of the subsurface at different scales. Many seismic velocity changes related to earthquakes and volcanic activities have been obtained using ambient noise correlation in recent years; however, their temporal resolution is limited, typically from a few to dozens of days, which makes it challenging to explore the valuable but short-duration changes in subsurface media. In this article, we develop a method based on the correlation of the coda of the ambient noise correlation (C3) with a multiple-component combination and introduced singular value decomposition-based Wiener filter denoising technique. Using permanent network data, we achieved subdaily ambient noise monitoring at Parkfield, California, using 4-hr cross-correlation stacking with 2-hr step. We identified that the maximum seismic velocity drop delayed the mainshock of the 2004 Mw 6.0 Parkfield earthquake by ∼41 hr, during which the temporal velocity process may have been affected by strong aftershocks, including an Mw 5.0 aftershock that occurred one day after the mainshock; however, no significant precursory change was detected. Our method provides an opportunity for monitoring the short-term change of underground structures based on the widely distributed seismic networks. In addition, the idea of obtaining reliable subsurface information within a short time through high-order noise correlation in this work has important enlightenment for ambient noise imaging and monitoring in broader fields.

On Suitability of Day-Night Average Sound Level Descriptor in Indian Scenario

The paper analyzes the monthly day equivalent levels, Lday (06–22h) and night equivalent levels, Lnight (22–06 h) values observed in year 2015 and 2016 for the 70 locations whereby continuous noise monitoring is conducted under the National Ambient Noise Monitoring Network (NANMN). The study exclusively analyzes the ambient noise data acquired for 25 locations in commercial zone, 12 in industrial, 16 in residential and 17 in silence zones. The analysis of (Lday–Lnight) for 70 locations under observations reveals that 10 dB night time adjustment in day-night average sound level descriptor is not appropriate in such a scenario and as such it is recommended to use day-night average sound level and day-evening-night average sound level descriptors without any 10 dB night time adjustment or 5 dB evening time adjustments. The analysis and conclusions of the present study shall be very useful for developing single value noise descriptor correlating the noise annoyance and health effects in Indian perspectives.

Boothless audiometry: Ambient noise considerations

Ambient noise in the test environment will impact signal detection during hearing threshold measurements due to psychoacoustic masking effects. Technical standards specify the maximum permissible ambient noise levels (MPANLs) for use during audiometric testing. MPANLs are dependent on several factors, including transducer characteristics (supra-aural, circumaural, type of ear cushions or earphone enclosures, and insert earphones), the nature of the hearing test being performed (air conduction vs bone conduction and threshold test vs screen at a suprathreshold level), and measurement instrumentation. The nature of the ambient noise (spectrum and constant vs variable) at the test site must be determined and continually accounted for during the boothless hearing test procedure. Ambient noise monitoring procedures are reviewed and examples of ambient noise characteristics in real-world settings, where hearing testing might be performed outside of a sound-treated environment, are provided. Practical considerations are presented, including examples of available tools for ambient noise monitoring, selection of test locations, and transducer attenuation. These are discussed in the context of calculating MPANLs and how best to ensure that ambient noise levels are not negatively impacting the validity of hearing thresholds.

Effect of lockdown amid second wave of COVID-19 on environmental noise scenario of the megacity Delhi, India.

This paper analyzes the impact of second wave of COVID-19 lockdown on environmental noise levels of 25 sites in Delhi city and compares the noise scenario during pre-lockdown, lockdown, and post-lockdown periods. The study utilized the noise monitoring data acquired from 25 real-time ambient noise monitoring stations, installed by the Delhi Pollution Control Committee, Delhi, at various sites throughout Delhi city. A significant reduction of up to 10 and 3 dB(A) in day and night equivalent noise levels, respectively, had been observed during the lockdown period as compared to the pre-lockdown and post-lockdown periods. The study also revealed that only nine sites, including four industrial and five commercial zone sites, complied with the ambient noise standards during lockdown period, and no silence or residential zone sites complied with the ambient noise standards even during the lockdown period. A roadmap for environmental noise management and control is suggested. The study also reports the community's perception toward the change in acoustic environment of Delhi city during the lockdown period by conducting an environmental noise perception survey. The present study should be helpful in devising noise control action plans and policy interventions for environmental noise management and control in the metropolitan city Delhi, India.

Home-Based Audiometry With a Smartphone App: Reliable Results?

The aim of this study was to assess the test-retest reliability of a smartphone-based hearing test, performed without supervision of a hearing professional in an uncontrolled environment. The hearing application is based on an automated hearing test (DuoTone) and relies on verification procedures (ambient noise monitoring algorithm, graphical user interface) to ensure appropriate measurement conditions. Thresholds obtained with DuoTone were compared to those obtained with standard clinical audiometry for 0.5, 1, 2, and 4 kHz in 13 subjects. Subsequently, test-retest reliability was analyzed using anonymized cloud-stored data from a large group of app users (1,641 subjects) who performed multiple hearing tests. Thresholds at minimum or maximum presentation level of the hearing test (10 dB HL, 85 dB HL) were excluded to avoid floor/ceiling effects. A subset (500 subjects) was created to exclude potentially unreliable data. Test-retest thresholds were compared at 12 test frequencies, from 125 Hz to 12 kHz. Thresholds determined by DuoTone and clinical audiometry did not differ significantly for each test frequency. Regarding test-retest analysis, the percentage of test-retest results within 5 dB ranged from 60% to 77% per test frequency. Results from the subset were not substantially different. Test-retest reliability for app users was comparable to results published in the literature regarding test-retest reliability of audiometry, performed in the clinic. Initial validation results suggest that thresholds obtained with DuoTone are comparable to clinical audiometry (four frequencies tested). The hearing app provides reliable hearing thresholds between 15 and 80 dB HL (12 frequencies tested) with a test-retest reliability comparable to clinical audiometry.

Ambient seismic noise monitoring and imaging at the Theistareykir geothermal field (Iceland)

In autumn 2017 a network of 14 broadband seismic stations was deployed at the Theistareykir high temperature geothermal field (NE Iceland). This experiment was conducted as part of the current efforts to characterize the field's main structures, and possible short and long term stress variations due to the ongoing fluid injection and extraction operations which started in autumn 2017. In this work, we use two years of continuous seismic records (October 2017–October 2019) to compute a 3D shear wave velocity model of the geothermal field and to detect possible crustal stress changes related to the injection and production activities. From phase cross-correlations of the vertical component recordings, we measure the Rayleigh wave group velocity dispersion curves to obtain 2D group velocity maps between 1 and 5 s. Subsequently, we use a neighborhood algorithm to retrieve the 3D shear wave velocity model of Theistareykir. Mainly, two sets of elongated high and low velocity anomalies can be observed oriented in a NW/WNW direction, parallel to the lineaments of the active Tjörnes fracture zone. Velocity reductions west of Ketilfjall and at Baerjafjall could indicate the location of upflow zones of the magmatic reservoir or hydrothermal system. We analyzed the temporal evolution of phase and amplitude of phase auto-correlations using the stretching technique and discuss their behavior in relation to the geothermal field operations. We notice a slightly stronger long-term velocity decrease in the reservoir region compared to outer regions. This could be related to the mass depletion in that area (higher fluid extraction compared to the water reinjection). In summary, our findings show how a monitoring network can be set up to enable a detailed imaging and monitoring of reservoir behavior in general.

Multi-site validation of shipping noise maps using field measurements

Underwater radiated noise from shipping is globally pervasive and can cause deleterious effects on marine life, ranging from behavioural responses to physiological effects. Acoustic modelling makes it possible to map this noise over large areas and long timescales, and to test mitigation scenarios such as ship speed reduction or spatial restrictions. However, such maps must be validated against measurements to ensure confidence in their predictions. This study carried out a multi-site validation of the monthly and annual shipping noise maps for 2019 produced as part of the Joint Monitoring of Ambient Noise in the North Sea (JOMOPANS) programme. Spectral, spatial, and temporal differences between predictions and measurements were analysed, with differences linked to uncertainty in model input data and additional sources of anthropogenic noise in the measurements. Validating shipping noise models in this way ensures they can be applied with confidence in future management decisions to address shipping noise pollution.

A CNN Based Software Gradiometer for Electromagnetic Background Noise Reduction in Low Field MRI Applications.

The shielding of electromagnetic noise is critical in obtaining magnetic resonance imaging measurements in the ultra-low magnetic field regime where the intrinsic signal-to-noise ratio is very small. The traditional approach of using an enclosure for electromagnetic shielding is expensive and hinders system portability. We describe here the use of a CNN-based software gradiometer to suppress the effect of electromagnetic ambient background noise sources that inductively couple into the signal detection coils. The system involves three ambient noise monitoring coils placed at a distance from the magnetic resonance signal detector. The three coils were used to synthesize the ambient noise captured by the signal detector; a convolutional neural network approach was used. Mathematical foundations are provided to justify the noise suppression framework. The results show that as much as 20-fold noise suppression can be achieved using an optimized convolutional neural network and simultaneous ambient noise measurements. The proposed approach has the potential to replace the requirement for magnetically shielded enclosures and make ultra-low field magnetic resonance imaging truly portable.

Ambient Noise Monitoring during Pure-Tone Audiometry.

There is an increasing need to administer hearing tests outside of sound-attenuating rooms. Maximum permissible ambient noise levels (MPANLs) from published in standards (Occupational Health and Safety Administration [OSHA] 1983; American National Standards Institute [ANSI] S3.1-1999 (R2018)) can be modified to account for the additional attenuation provided by circumaural earphones (relative to supra-aural earphones) that are used for pure-tone audiometry. Ambient noise can influence the results of pure-tone audiometry by elevating thresholds by direct masking and by producing distractions that affect the accuracy of the test. The effects of these distractions have not been studied in relation to pure-tone audiometry in adult listeners. In Part I MPANLs provided by ANSI and OSHA standards are extended to account for the greater attenuation provided by circumaural earphones. Rules ("alerts") were developed taking into account the listeners' thresholds. In Part II effects of distracting noise on pure-tone thresholds are reported. In Part I MPANLs two standards were modified for circumaural earphones by adding the additional attenuation provided by three circumaural earphones (relative to supra-aural earphones). A set of rules ("alerts") is provided for identifying masking effects from ambient noise in a variety of conditions (earphone type, threshold elevation, uncovered ear). In Part II the distracting effects of an industrial noise sample on thresholds obtained from five listeners with normal hearing are described. Pure-tone thresholds were measured in quiet and in distracting noise presented at various levels. The effects of the distracting noise on the following variables were measured: time per trial, number of trials required to measure threshold, threshold shift, and perceived distractibility of the noise. Time per trial was unaffected by distracting noise. Number of trials required for threshold, threshold shift, and perceived distractibility increased with distracting noise level. Part I: The modified MPANLs provide more relevant determinations of the potential effects of ambient noise on pure-tone thresholds than the values in the standards. Part II: Distracting noise affects pure-tone threshold measurements in a manner that is different from direct masking. The potential contaminating effect of distracting noise can be measured and reported.

Detecting Elevated Pore Pressure due to Wastewater Injection Using Ambient Noise Monitoring

Abstract The injection of large volumes of wastewater has induced earthquakes from June 2010 to July 2011 along the Guy–Greenbrier fault in Arkansas. We measure time-dependent changes in seismic velocities underneath three temporary seismic stations, using the daily autocorrelations of ambient seismic noise. We do not find any effect of the pumping rate or volume injected in the changes in velocity. However, the induced earthquakes’ ground motions are associated with an extreme reduction in seismic velocities. The magnitude of the changes surpasses ten times the values typically found in other earthquake settings. Our full-waveform investigation suggests that the changes mainly occurred around the top of the Ozark aquifer. We interpret these extreme changes as a result of dynamic shaking in the elevated pore pressure system of the Ozark aquifer.

Anthropogenic noise variation in Indian cities due to the COVID-19 lockdown during March-to-May 2020.

This paper analyzes the impact of a nationwide lockdown enforced during March-to-May 2020 to prevent the widespread transmission of COVID-19 on the local anthropogenic noise level variation in Indian cities. To this end, data obtained from the National Ambient Noise Monitoring Network (NANMN) was used to analyze the long-term daily evolution of average day- and night-time levels at selected locations across seven major cities. The results indicate that when the strict lockdown phase 1 was declared, all industrial (I), commercial (C), and residential (R) zones experienced either a gradual or sudden decrease in noise levels while the silence (S) zone was unaffected. Depending on the zone, the weekly trend graphs reached a minimum either during phase 1 or conditionally relaxed phase 2. Across I, C, and R zones, the average maximum day- and night-time reduction with respect to the pre-lockdown period ranged from 4 to 13.8 dB(A) and 4 to 14.1 dB(A), respectively. As anticipated, with a gradual ease in restrictions from phase 2 onwards, the levels climbed back almost linearly, and during unlocks, the daily variation resembled the pre-lockdown trend. Furthermore, the responses to an online COVID-19 noise perception survey supported the NANMN results and suggested that the lockdown was quieter.

Detecting Elevated Pore Pressure in the Guy-Greenbrier Fault Zone using Ambient Noise Monitoring

Detecting Elevated Pore Pressure in the Guy-Greenbrier Fault Zone using Ambient Noise Monitoring

Detecting Elevated Pore Pressure in the Guy-Greenbrier Fault Zone using Ambient Noise Monitoring

Detecting Elevated Pore Pressure in the Guy-Greenbrier Fault Zone using Ambient Noise Monitoring

Detecting Elevated Pore Pressure in the Guy-Greenbrier Fault Zone using Ambient Noise Monitoring

Detecting Elevated Pore Pressure in the Guy-Greenbrier Fault Zone using Ambient Noise Monitoring