Sound Exposure Level Research Articles

The Study of Estimation Method for Sound Exposure Level Taking Account to Ocean Environment and Moving of Source and Receiver

The Study of Estimation Method for Sound Exposure Level Taking Account to Ocean Environment and Moving of Source and Receiver

Long-Term Patterns of Noise From Underwater Explosions and Their Relation to Fisheries in Southern California

Acoustic deterrents can reduce marine mammal interactions with fisheries and aquacultures, but they contribute to an increasing level of underwater noise. In Southern California, commercially produced explosive deterrents, commonly known as “seal bombs,” are used to protect fishing gear and catch from pinniped predation, which can cause extensive economic losses for the fishing community. Passive acoustic monitoring data collected between 2005 and 2016 at multiple sites within the Southern California Bight and near Monterey Bay revealed high numbers of these small-charge underwater explosions, long-term, spatio-temporal patterns in their occurrence, and their relation to different commercial purse-seine fishing sectors. The vast majority of explosions occurred at nighttime and at many nearshore sites high explosion counts were detected, up to 2,800/day. Received sound exposure levels of up to 189 dB re 1 μPa2-s indicate the potential for negative effects on marine life, especially in combination with the persistence of recurring explosions during periods of peak occurrence. Due to the highly significant correlation and similar spatio-temporal patterns of market squid landings and explosion occurrence at many sites, we conclude that the majority of the recorded explosions come from seal bombs being used by the California market squid purse-seine fishery. Additionally, seal bomb use declined over the years of the study, potentially due to a combination of reduced availability of market squid driven by warm water events in California and regulation enforcement. This study is the first to provide results on the distribution and origin of underwater explosions off Southern California, but there is a substantial need for further research on seal bomb use in more recent years and their effects on marine life, as well as for establishing environmental regulations on their use as a deterrent.

Low-Noise Design of Medium-Range Aircraft for Energy Efficient Aviation

Promising low-noise aircraft architectures have been identified over the last few years at DLR. A set of DLR aircraft concepts was selected for further assessment in the context of sustainable and energy-efficient aviation and was established at the TU Braunschweig in 2019, the Cluster of Excellence for Sustainable and Energy-Efficient Aviation (SE2A). Specific Top-Level aircraft requirements were defined by the cluster and the selected DLR aircraft designs were improved with focus on aircraft noise, emissions, and contrail generation. The presented paper specifically addresses the reduction of aviation noise with focus on noise shielding and modifications to the flight performance. This article presents the state of the art of the simulation process at DLR and demonstrates that the novel aircraft concepts can reduce the noise impact by up to 50% in terms of sound exposure level isocontour area while reducing the fuel burn by 6%, respective to a conventional aircraft for the same mission. The study shows that a tube-wing architecture with a top-mounted, forward-swept wing and low fan pressure ratio propulsors installed above the fuselage at the wing junction can yield significant noise shielding at improved low-speed performance and reduce critical fuel burn and emissions.

Sperm whales exhibit variation in echolocation tactics with depth and sea state but not naval sonar exposures

AbstractAuditory masking by anthropogenic noise may impact marine mammals relying on sound for important life functions, including echolocation. Animals have evolved antimasking strategies, but they may not be completely effective or cost‐free. We formulated seven a priori hypotheses on how odontocete echolocation behavior could indicate masking. We addressed six of them using data from 15 tagged sperm whales subject to experimental exposures of pulsed and continuous active sonar (PAS and CAS). Sea state, received single‐pulse sound exposure level (SELsp), whale depth and orientation towards surface, and sonar were considered as candidate covariates representing different masking conditions. Echolocation behavior, including buzz duration and search range, varied strongly with depth. After controlling for depth and angle to the surface, the likelihood of buzzing following a click train decreased with sea state (t = −7.3, p < .001). There was little evidence for changes in 10 tested variables with increasing sonar SELsp, except reduced buzzing consistent with previously reported feeding cessation (t = −2.26, p = .02). A potential Lombard effect was detected during echolocation with sea state and SELsp, despite off‐axis measurement and right‐hand censoring due to acoustic clipping. The results are not conclusive on masking effects on sperm whale echolocation, highlighting challenges and opportunities for future anthropogenic masking studies.

Sound pressure and particle motion components of the snaps produced by two snapping shrimp species (Alpheus heterochaelis and Alpheus angulosus)

Snapping shrimps are pervasive generators of underwater sound in temperate and tropical coastal seas across oceans of the world. Shrimp snaps can act as signals to conspecifics and provide acoustic information to other species and even to humans for habitat monitoring. Despite this, there are few controlled measurements of the acoustic parameters of these abundant acoustic stimuli. Here, the characteristics of snaps produced by 35 individuals of two species, Alpheus heterochaelis and Alpheus angulosus, are examined to evaluate the variability within and between the species. Animals were collected from the wild and the sound pressure and particle acceleration were measured at 0.2, 0.5, and 1 m from individual shrimp in controlled laboratory conditions to address the snap properties at communication-relevant distances. The source and sound exposure levels (at 1 m) were not significantly different between these two species. The frequency spectra were broadband with peak frequencies consistently below 10 kHz. The particle acceleration, the sound component likely detectable by shrimp, was measured across three axes. The directional amplitude variation suggests that the particle motion of snaps could act as a localization cue. The amplitudes of the snap pressure and acceleration decreased with distance, yet the levels remained sufficient for the predicted detection range by nearby conspecifics.

Narwhals react to ship noise and airgun pulses embedded in background noise.

Anthropogenic activities are increasing in the Arctic, posing a threat to niche-conservative species with high seasonal site fidelity, such as the narwhal Monodon monoceros. In this controlled sound exposure study, six narwhals were live-captured and instrumented with animal-borne tags providing movement and behavioural data, and exposed to concurrent ship noise and airgun pulses. All narwhals reacted to sound exposure with reduced buzzing rates, where the response was dependent on the magnitude of exposure defined as 1/distance to ship. Buzzing rate was halved at 12 km from the ship, and whales ceased foraging at 7–8 km. Effects of exposure could be detected at distances > 40 km from the ship.At only a few kilometres from the ship, the received high-frequency cetacean weighted sound exposure levels were below background noise indicating extreme sensitivity of narwhals towards sound disturbance and demonstrating their ability to detect signals embedded in background noise. The narwhal's reactions to sustained disturbance may have a plethora of consequences both at individual and population levels. The observed reactions of the whales demonstrate their auditory sensitivity but also emphasize, that anthropogenic activities in pristine narwhal habitats needs to be managed carefully if healthy narwhal populations are to be maintained.

Explosives Use in Decommissioning—Guide for Assessment of Risk (EDGAR): II Determination of Sound Exposure Levels for Open Water Blasts and Severance of Conductors and Piles from below the Seabed

A simple underwater noise model suitable for use with explosive severance of well conductors and piles during the decommissioning of oil and gas subsea structures is introduced and evaluated against data from five projects in the US. This study focuses on a novel model for the determination of sound exposure levels. The model has been developed to enable determination of impact areas for marine mammals and fish. Simulated received underwater sound exposure levels were significantly correlated with measurements for all scenarios. The maximum total error achieved between simulations and measurements was 2.6%, suggesting that predictions are accurate to within 3% of the average measurement. A low relative bias was observed in the simulations when compared to measured values, suggesting only a small systematic underestimate (≤0.5% of average measurement) for most severance operations and a small overestimate (0.14%) for open water blasts.

Farmed Salmon Show No Pathological Alterations When Exposed to Acoustic Treatment for Sea Lice Infestation

The use of bioacoustic methods to address sea lice infestation in salmonid farming is a promising innovative method but implies an exposure to sound that could affect the fish. An assessment of the effects of these techniques related to the salmon’s welfare is presented here. The fish were repeatedly exposed to 350 Hz and 500 Hz tones in three- to four-hour exposure sessions, reaching received sound pressure levels of 140 to 150 dB re 1 µPa2, with the goal of reaching total sound exposure levels above 190 dB re 1 µPa2 s. Gross pathology and histopathological analysis performed on exposed salmons’ organs did not reveal any lesions that could be associated to sound exposure. The analysis of their otoliths through electron microscopy imaging confirmed that the sound dose that was used to impair the lice had no effects on the fish auditory organs.

Underwater implosion of re-enforced concrete piers

From 2015 through 2018, 18 reinforced concrete piers formally supporting the east span of the San Francisco-Oakland Bay Bridge were removed using underwater demolition. The events ranged from one pier to up three piers at one time with the number of charges ranging from 92 to 688 and weights from 12 to 35 pounds. In all cases, a bubble curtain, blast attenuation system was used to reduce the blast pressures. Although the blast plans varied, more variation in the monitored peak sound pressure levels and sound exposure levels was observed than was expected from initial predictions. Potential causes of this variability were examined including varying charge confinement, directionality due to self-shielding of the structures as the individual blasts progressed, the effect of varying distance to the monitoring location for the individual charges, obscuration of the monitoring location due to intervening structures, and varying effectiveness of the blast attenuation system. Each of these potential causes are examined in this presentation.

Investigating the impact of ambient noise on candidate sonic boom metrics

One goal of NASA’s X-59 flight campaign will be to collect low-amplitude sonic boom data over several communities. The combination of lower-amplitude booms with greater ambient noise could pose challenges in measuring and calculating accurate sonic boom perception metrics intended to be correlated with human annoyance. This study uses two NASA sonic boom flight test and simulated X-59 datasets to investigate the impact of limited measurement bandwidth due to ambient noise for multiple candidate metrics. An estimate of the signal-to-noise ratio spectrum allows for the comparison of metrics calculated with full bandwidth, limited bandwidth, and those calculated by applying a low-pass filter that approximates a noise-free full-bandwidth spectrum. The low-pass filter is chosen to approximately match the expected high-frequency roll-off of the sonic booms. Results indicate that Perceived Level and A-weighted sound exposure level are strongly affected by ambient noise and bandwidth limitations, but that B-weighted sound exposure level is much less affected. These results contribute to community noise test planning by demonstrating the ambient noise impact on candidate sonic boom perception metrics. [Work supported by NASA Langley Research Center through National Institute of Aerospace.]

Acoustic characteristics from an in-water down-the-hole pile drilling activity

Sound generated by pile installation using a down-the-hole (DTH) hammer is not well documented and differs in character from sound generated by conventional impact and vibratory pile driving. This paper describes underwater acoustic characteristics from DTH pile drilling during the installation of 0.84-m shafts within 1.22-m steel piles in Ketchikan, Alaska. The median single-strike sound exposure levels measured at 10 m were 138 and 142 dB re 1 μPa2 s for each of the two piles, with cumulative sound exposure levels of 188 and 193 dB re 1 μPa2 s at 10 m, respectively. The sound levels measured at Ketchikan were significantly lower than previous studies, and the sound is determined to be non-impulsive in this study as compared to impulsive in the previous studies. These differences likely result from fact that the DTH hammer used at Ketchikan did not make direct contact with the pile, as had been the case in previous studies. Further research is needed to investigate DTH piling techniques and associated sound-generating mechanisms, and to differentiate the various types of sound emitted.

Validation of an airline pilot assistant system for low-noise approach procedures

• Considerable noise reduction potential of pilot assistance system demonstrated. • Average sound exposure levels reduced by up to 1.8 dBA during final approach. • Average sound exposure levels reduced by up to 2.5 dBA in far range. • Elimination of particularly loud approaches. The recently developed airline pilot assistance system LNAS (Low Noise Augmentation System) supports pilots in optimizing approaches in terms of fuel consumption and noise emission by predicting the optimal vertical trajectory and best speed, configuration, and landing gear setting. The system continuously updates recommendations to provide the energy-optimal profile at any time. The noise reduction potential of the latest LNAS version was tested during a flight campaign in 2019 at Zurich Airport, Switzerland, using a dedicated Airbus A320 research aircraft. 43 LNAS-assisted and 21 conventional approaches were analyzed. Acoustic measurements taken at six microphone positions along the glide path revealed reductions in average sound exposure levels of up to 1.8 dBA when LNAS was used. Complementing detailed single-flight simulations using the aircraft noise program sonAIR confirmed the large noise reduction potential of LNAS, which may help reducing sound exposure in certain areas by up to 2.5 dBA.

A construction for the prediction of noise-induced annoyance in the presence of auditory masking

There is a large amount of evidence to suggest that people’s reactions to annoying sounds are moderated by the presence of other background sounds. One of the mechanisms of this moderation is auditory masking: when the annoying sound simply cannot be heard over the background. This presentation outlines a construction for computing a predictor of annoyance in the presence of masking. The construction is demonstrated by producing an augmentation of the common sound exposure level noise metric using one-third octave band data sampled at 2 Hz. These data allow an estimation of the probability of masking within each band at each time step. The acoustic energy within a masked band can be ‘discounted’ by this estimation before being summed in the usual equal-energy way and with the typical A-weighting corrections. In this way, backgrounds that only provide partial masking in frequency and time will produce predictions of annoyance that fall between the unmasked sound exposure value and negative infinity (the result if there was a certainty of complete masking). The application of this concept to the noise of multirotor air vehicles is discussed.

Underwater noise mitigation in the Santa Barbara Channel through incentive-based vessel speed reduction

Commercial shipping is the dominant source of low-frequency noise in the ocean. It has been shown that the noise radiated by an individual vessel depends upon the vessel’s speed. This study quantified the reduction in source levels (SLs) and sound exposure levels (SELs) for ships participating in two variations of a vessel speed reduction (VSR) program. SLs and SELs of individual ships participating in the program between 2014 and 2017 were statistically lower than non-participating ships (p < 0.001). In the 2018 fleet-based program, there were statistical differences between the SLs and SELs of fleets that participated with varying degrees of cooperation. Significant reductions in SL and SEL relied on cooperation of 25% or more in slowing vessel speed. This analysis highlights how slowing vessel speed to 10 knots or less is an effective method in reducing underwater noise emitted from commercial ships.

Seal bomb explosion sound source characterization.

Small explosive charges, called seal bombs, used by commercial fisheries to deter marine mammals from depredation and accidental bycatch during fishing operations, produce high level sounds that may negatively impact nearby animals. Seal bombs were exploded underwater and recorded at various ranges with a calibrated hydrophone to characterize the pulse waveforms and to provide appropriate propagation loss models for source level (SL) estimates. Waveform refraction became important at about 1500 m slant range with approximately spherical spreading losses observed at shorter ranges. The SL for seal bombs was estimated to be 233 dB re 1 μPa m; however, for impulses such as explosions, better metrics integrate over the pulse duration, accounting for the total energy in the pulse, including source pressure impulse, estimated as 193 Pa m s, and sound exposure source level, estimated as 197 dB re 1 μPa2 m2 s over a 2 ms window. Accounting for the whole 100 ms waveform, including the bubble pulses and sea surface reflections, sound exposure source level was 203 dB re 1 μPa2 m2 s. Furthermore, integrating the energy over an entire event period of multiple explosions (i.e., cumulative sound exposure level) should be considered when evaluating impact.

Damped cylindrical spreading model: Estimation of mitigated pile driving noise levels

Underwater noise caused by impulsive pile driving for the installation of foundations for offshore wind farms is potentially harmful to marine life if not properly mitigated. Several models have been developed over the past years, to accurately predict the underwater sound field from pile driving activities. However, due to the complexity of the problem and subsequently the corresponding models, the use of such models is often restricted to a relatively small group of experts. To enable a wider group of people to estimate at least the sound exposure level (SEL), as one of the key quantities, the Damped Cylindrical Spreading (DCS) model has been developed recently and validated using measurement data from unmitigated pile driving. The paper at hand now aims at extending the DCS model to the case of mitigated pile driving noise, using corresponding measurement data from five offshore sites in the North Sea. Furthermore, the potential of the model to predict noise levels in close vicinity of the pile is investigated. Based on the available data sets, it is shown that the approach can indeed be extended to mitigated pile driving scenarios including short range levels as well as different noise mitigation techniques and foundation types, while still producing results that are more accurate than the currently most widely used approach for sound decay estimations.

Subtraction Analysis for Predicting the Propagation Effects of Aircraft Noise

In 2013, the Federal Aviation Administration and Volpe National Transportation System Center conducted a series of acoustic measurements with a propeller driven aircraft operating in the regions near Houston, Texas. The recorded data on octave band sound levels, aircraft locations, temperature and wind speed profiles were used in the current study to quantify the uncertainties for predicting the propagation effects of aircraft noise. Use of the Aviation Environmental Design Tool (AEDT) was explored for its accuracy and validity in real world scenarios offered by the dataset. The sound exposure level (SEL) data for each section of a flight path was used instead of the time history data for reducing the directivity effect of the sound source due to the change in its relative positions with the receivers. A subtraction-based method was introduced to analyze the propagation effect in which the SELs between two receiver locations were compared. The use of the subtraction method reduces the possible influences of the sound power variations along the flight paths. The measured data for a spiral and a level flight event were presented and the AEDT predictions on the propagation effects were examined in this paper.

Comments on "Influences of low-frequency energy and testing environment on annoyance responses to supersonic aircraft noise when heard indoors" [J. Acoust. Soc. Am. 148(1), 414-429 (2020)

Carr, Davies, Loubeau, Rathsam, and Klos [J. Acoust. Soc. Am. 148, 414-429 (2020)] found that indoor annoyance caused by sonic booms may be predicted from the A-weighted sound exposure level and the heaviness of the booms. Moreover, they suggest that, irrespective of the outdoor-to-indoor sound reduction, indoor annoyance may be predicted from outdoor sound levels. The present paper shows that their data to some extent also support a model in which the contribution of heaviness is level-dependent and that data reported in the literature point out that it is unlikely that indoor annoyance is independent of the degree of façade attenuation.

An experiment on the feeling of separation when multiple aircraft noises are overlapped

In order to calculate the A-weighted single event sound exposure level () of aircraft noise, the following method is described in the manual for aircraft noise measurement in Japan. Firstly a time-section, which is the range between two points where the noise level is 10 dB lower than the maximum noise level (), should be identified, and secondly the energy within the section is integrated. This method can easily be applied to the single event noises. When multiple aircraft noises are overlapped simultaneously, there are cases where cannot be calculated adequately by this method. In such cases, it is required to record the number of aircraft noises in the field measurements. However, even in the case of manned measurement, it is not easy to separate sound sources just by listening to the sound. A pilot study of the psychoacoustic experiment was conducted using the stimuli where multiple aircraft noises were overlapped in order to find what condition is needed so that multiple aircraft noises were separately perceived. It was suggested that a considerable time interval was needed so that people felt the separation between aircraft noises only with auditory information.

Shooting noise annoyance in communities around German military training areas

Shooting noise is characterized as impulsive, intermittent sound with high energy and low frequencies. Studies have shown that for given average sound levels shooting noise is regarded as more annoying than transportation noise, particularly road traffic noise. In comparison to transportation noise, responses to shooting noise are less frequently studied. The latest published German studies on community responses to shooting noise were conducted in the 1980ies and 1990ies. The study presented in this contribution aims to provide new data on shooting noise responses in communities around military training areas. Annoyance responses were collected using a survey with 1043 residents living around three military training sites in Germany. For the address of each resident, on the basis of shooting training in the year 2019 the average continuous sound levels and the sound exposure levels for day and night-time with the frequency weightings A, C, and Z was estimated for grid cells of 250 x 250 m. Results on the exposure-response relationship between these noise metrics and the percentage of highly annoyed persons (%HA) are presented. Among others, the results indicate, that non-acoustic factors, particularly attitudes related to the source have a strong impact on the annoyance.