Airgun Sounds Research Articles

Estimates of geoacoustic parameters and source range using airgun sound in the East Siberian Sea, Arctic Ocean

In a shallow-water waveguide, low-frequency sound propagating over several kilometers has dispersive properties and thus the dispersion curves can be used for the inversion of geoacoustic parameters. In September 2019, seismic survey was conducted by the icebreaking research vessel Araon, operated by Korea Polar Research Institute. A single hydrophone was moored at East Siberian Shelf, a nearly range-independent shallow water (<70 m), to receive seismic airgun sounds generated from the R/V Araon. It was observed that the arrivals corresponding to the first two modes were clearly dispersed in the spectrogram of the received signal. In order to use these dispersion curves for the geoacoustic inversion, the dispersion curves corresponding to the first two modes were extracted using the warping transform combined with the wavelet synchrosqueezing transform. Geoacoustic parameters including sound speed and density in the sediment and the distance between the source and receiver were then estimated by comparing the extracted dispersion curves to the model replicas predicted by the KRAKEN normal-mode acoustic propagation model. Finally, the inversion results and their error analysis will be discussed in this talk. [This research was a part of the project titled ‘Korea-Arctic Ocean Warming and Response of Ecosystem (K-AWARE, KOPRI, 1525011760)’, funded by the Ministry of Oceans and Fisheries, Korea and supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2020R1A2C2007772).]

Acoustic characteristics of the seismic airgun sound propagation in the East Siberian Sea

A passive acoustic monitoring has been conducted by Korea Polar Research Institute (KOPRI) since 2017 in the East Siberian Sea using an autonomous passive acoustic recorder. Seismic airgun sounds, generated from the multichannel seismic survey system of the ice-breaking research vessel Araon, were measured from 18.6 km to 164.2 km in September 2019. During the survey, the R/V Araon maintained the ship’s trajectory at a constant heading and speed to obtain useful acoustic data for investigating the acoustic propagation properties with a distance between the source and receiver in shallow water. The decrease in sound pressure levels as a function of distance was compared with the least-square regression curves and numerical propagation modeling based on the parabolic equation. The broadband sounds in a low-frequency range were propagated over long distances with distinctive characteristics such as precursor arrivals, modal dispersion, and rapid decrease in spectrum level at low frequencies. Our results will be discussed in comparison with the sediment structure and geological history of the measurement region. [This research was supported by Korea Institute of Marine Science & Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries (20210605, Korea-Arctic Ocean Warming and Response of Ecosystem, KOPRI and 20210632, Survey of Geology and Seabed Environmental Change in the Arctic Seas, KOPRI).]

Effects of seismic airgun playbacks on swimming patterns and behavioural states of Atlantic cod in a net pen

Anthropogenic sound can affect fish behaviour and physiology which may affect their well-being. However, it remains a major challenge to translate such effects to consequences for fitness at an individual and population level. For this, energy budget models have been developed, but suitable data to parametrize these models are lacking. A first step towards such parametrization concerns the objective quantification of behavioural states at high resolution. We experimentally exposed individual Atlantic cod (Gadus morhua) in a net pen to the playback of seismic airgun sounds. We demonstrated that individual cod in the net pen did not change their swimming patterns immediately at the onset of the sound exposure. However, several individuals changed their time spent in three different behavioural states during the 1 h exposure. This may be translated to changes in energy expenditure and provide suitable input for energy budget models that allow predictions about fitness and population consequences.

Lack of reproducibility of temporary hearing threshold shifts in a harbor porpoise after exposure to repeated airgun sounds.

Noise-induced temporary hearing threshold shift (TTS) was studied in a harbor porpoise exposed to impulsive sounds of scaled-down airguns while both stationary and free-swimming for up to 90 min. In a previous study, ∼4 dB TTS was elicited in this porpoise, but despite 8 dB higher single-shot and cumulative exposure levels (up to 199 dB re 1 μPa2s) in the present study, the porpoise showed no significant TTS at hearing frequencies 2, 4, or 8 kHz. There were no changes in the study animal's audiogram between the studies or significant differences in the fatiguing sound that could explain the difference, but audible and visual cues in the present study may have allowed the porpoise to predict when the fatiguing sounds would be produced. The discrepancy between the studies may have resulted from self-mitigation by the porpoise. Self-mitigation, resulting in reduced hearing sensitivity, can be achieved via changes in the orientation of the head, or via alteration of the hearing threshold by processes in the ear or central nervous system.

Effect of a Bubble Screen on the Behavioral Responses of Captive Harbor Porpoises (Phocoena phocoena) Exposed to Airgun Sounds

Effect of a Bubble Screen on the Behavioral Responses of Captive Harbor Porpoises (Phocoena phocoena) Exposed to Airgun Sounds

Sounds from airguns and blue whales recorded from a long term hydrophone network in the Southern Indian Ocean

The Southern Indian Ocean is a seasonal habitat for different blue whale sub species and sub populations. Their presence has been demonstrated by continuous acoustic records from the OHASISBIO hydrophone network, deployed since 2010 and which comprises 5 to 9 fixed mooring sites spread over a region from 24 deg to 56 deg South and from 52 deg to 83 deg East. Automated detection based on dictionaries and sparse representation has been used to detect and count the different stereotyped or non-stereotyped calls emitted by blue whales and recorded in this long-term dataset. However false alarm rate increased sometimes by the detection of a recurrent interference in the same frequency band of blue whales: the airgun shots produce during surveys for oil and gas located somewhere in the Indian Ocean and beyond. This finding allows us to characterize the seasonal and interannual variability in airgun sounds in this blue whale habitat. This study reinforce the fact that anthropogenic noise could be detected at large scale in pelagic environment and may affect marine mammal specially species who used low frequency bands.

Guest Editorial: The International Airgun Modeling Workshop

The papers in this special issue had its origins in the International Airgun Modeling Workshop (the Workshop), which took place in Dublin, Ireland, on July 16, 2016. The purpose of the Workshop was to address the demand for increasingly precise assessment of the environmental impacts of seismic surveys. However, an increase in precision requires accurate characterization of the sound field radiated by an airgun array, including the interface between source signature models and sound propagation models. The impacts of airgun sounds on marine life are predicted by first deriving the sound field through a combination of source signature models with sound propagation models. Impact ranges are then estimated according to acoustic criteria, and that information can be further analyzed by assessing risks to local densities and populations. The Workshop scope included modeling of the airguns’ signatures and of the sound field at distances from a few meters to a few tens of kilometers from each source, including the near field of a realistic airgun array. In addition to sound pressure, participants were requested to calculate sound particle acceleration because of its importance to fishes and invertebrates.

Estimation of subbottom geoacoustic properties from offshore airgun surveys in Atlantic Canada

This paper estimates seabed geoacoustic profiles at 14 sites offshore of the eastern Canadian coast using sound levels from a single airgun. A 210 in3 airgun was operated along two track lines at each site and a calibrated seabed-mounted Autonomous Multichannel Acoustic Recorder equipped with a single omnidirectional hydrophone recorded the airgun sounds. High-resolution bathymetry was acquired along the tracks using a ship-mounted multibeam system and conductivity-temperature-depth profiles were measured at each site. Seabed geoacoustic profiles were estimated in a non-linear trans-dimensional Bayesian inversion using energy spectral density levels at six frequencies between 10 and 320 Hz as a function of range. The inversion estimated the unknown number of subbottom layers, geoacoustic properties (including compressional and shear wave speeds and attenuations, density, and layer thicknesses), airgun source levels, a range-correction factor, and error statistics. Data were fit with error standard deviations of 0.6–5.6 dB. Convergence of the posterior probability density function was not reached within the time limits of the study so parameter uncertainty was estimated using a linearized formulation of the inverse problem centered around the model that minimized the Bayesian Information Criterion.This paper estimates seabed geoacoustic profiles at 14 sites offshore of the eastern Canadian coast using sound levels from a single airgun. A 210 in3 airgun was operated along two track lines at each site and a calibrated seabed-mounted Autonomous Multichannel Acoustic Recorder equipped with a single omnidirectional hydrophone recorded the airgun sounds. High-resolution bathymetry was acquired along the tracks using a ship-mounted multibeam system and conductivity-temperature-depth profiles were measured at each site. Seabed geoacoustic profiles were estimated in a non-linear trans-dimensional Bayesian inversion using energy spectral density levels at six frequencies between 10 and 320 Hz as a function of range. The inversion estimated the unknown number of subbottom layers, geoacoustic properties (including compressional and shear wave speeds and attenuations, density, and layer thicknesses), airgun source levels, a range-correction factor, and error statistics. Data were fit with error standard deviati...

Temporary hearing threshold shift in a harbor porpoise (Phocoena phocoena) after exposure to multiple airgun sounds.

In seismic surveys, reflected sounds from airguns are used under water to detect gas and oil below the sea floor. The airguns produce broadband high-amplitude impulsive sounds, which may cause temporary or permanent threshold shifts (TTS or PTS) in cetaceans. The magnitude of the threshold shifts and the hearing frequencies at which they occur depend on factors such as the received cumulative sound exposure level (SELcum), the number of exposures, and the frequency content of the sounds. To quantify TTS caused by airgun exposure and the subsequent hearing recovery, the hearing of a harbor porpoise was tested by means of a psychophysical technique. TTS was observed after exposure to 10 and 20 consecutive shots fired from two airguns simultaneously (SELcum: 188 and 191 dB re 1 μPa2s) with mean shot intervals of around 17 s. Although most of the airgun sounds' energy was below 1 kHz, statistically significant initial TTS1-4 (1-4 min after sound exposure stopped) of ∼4.4 dB occurred only at the hearing frequency 4 kHz, and not at lower hearing frequencies tested (0.5, 1, and 2 kHz). Recovery occurred within 12 min post-exposure. The study indicates that frequency-weighted SELcum is a good predictor for the low levels of TTS observed.

Changes in Fish Catch Rates in the Presence of Air Gun Sounds in Prudhoe Bay, Alaska

Air guns used in oil industry seismic surveys have the capacity to change fish catch rates, but no previous work has demonstrated this effect in shallow water or in Arctic oilfields. Long-term monitoring of fish catches using four fyke nets allowed assessment of changes in catch rates during a 2014 seismic survey in Prudhoe Bay, Alaska. Fyke net locations were instrumented with both conventional hydrophones and vector sensors. Catch rates were generally within the range of those found in 27 previous sampling seasons. The effect of air guns on eight species was assessed using a modified Before-After/Control-Impact analysis, with historical data and 2014 data as the Before-After components of the analysis and days without and with air gun activity as the Control-Impact components. Results showed significant changes associated with air guns in catch rates at one or more nets at p < 0.1 for all eight species and at p < 0.05 for seven of the eight. Changes included both increased and decreased catch rates, perhaps reflecting displacement of fish in response to air gun sounds throughout the study area. Measured sound pressure levels associated with air gun pulses were low and usually undetectable close to the fyke nets, reflecting the loss of low frequencies in shallow water (~1.5 m). Attempts to measure particle velocities failed when wind-driven surface waves overwhelmed vector sensors. However, fish responses may have been related to changes in particle motion associated with air gun sounds.

Long range sound propagation modeling for assessing seismic survey noise impacts on marine mammals

Despite of small land area, Japan has vast EEZ, which is expected to have potential mineral resources. Extensive seismic surveys have been conducted for those targets. However, airguns used for the survey generate intense and low-frequency impulse sound, which could disturb or harm marine mammal behavior and auditory system. In June 2016, NOAA released “Ocean Noise Strategy Roadmap” that recommends modeling of sound propagation in the context of realistic environmental parameters to assess noise impacts on marine creatures. Japan has remarkable seasonal climate changes and complex ocean-bottom topography with trenches and seamounts; therefore, such model is worthwhile. Here, we propose a modeling method utilizing ARGO data includes seasonal climate changes and LEVITUS data, and ocean-bottom topographic configuration data from Google Earth. We calculated long range propagation of airgun sounds in different sound profiles and ocean-bottom topographic configurations around Ogasawara Islands, which is known as a cetacean habitat. Results showed that seasonal climate change and the precision of the ocean-bottom topographic configuration caused significant differences in sound propagation. These findings suggest that the realistic environmental parameters is essentially needed for the modeling of sound propagation and proposed method is a useful tool to assess noise impacts on marine mammals.

Effects of airgun sounds on bowhead whale calling rates: evidence for two behavioral thresholds.

In proximity to seismic operations, bowhead whales (Balaena mysticetus) decrease their calling rates. Here, we investigate the transition from normal calling behavior to decreased calling and identify two threshold levels of received sound from airgun pulses at which calling behavior changes. Data were collected in August–October 2007–2010, during the westward autumn migration in the Alaskan Beaufort Sea. Up to 40 directional acoustic recorders (DASARs) were deployed at five sites offshore of the Alaskan North Slope. Using triangulation, whale calls localized within 2 km of each DASAR were identified and tallied every 10 minutes each season, so that the detected call rate could be interpreted as the actual call production rate. Moreover, airgun pulses were identified on each DASAR, analyzed, and a cumulative sound exposure level was computed for each 10-min period each season (CSEL10-min). A Poisson regression model was used to examine the relationship between the received CSEL10-min from airguns and the number of detected bowhead calls. Calling rates increased as soon as airgun pulses were detectable, compared to calling rates in the absence of airgun pulses. After the initial increase, calling rates leveled off at a received CSEL10-min of ~94 dB re 1 μPa2-s (the lower threshold). In contrast, once CSEL10-min exceeded ~127 dB re 1 μPa2-s (the upper threshold), whale calling rates began decreasing, and when CSEL10-min values were above ~160 dB re 1 μPa2-s, the whales were virtually silent.

Effects of airgun sounds on bowhead whale calling rates in the Alaskan Beaufort Sea

AbstractThis study assesses effects of airgun sounds on bowhead calling behavior during the autumn migration. In August–October 2007, 35 directional acoustic recorders (DASARs) were deployed at five sites in the Alaskan Beaufort Sea. Location estimates were obtained for >137,500 individual calls; a subsample of locations with high detection probability was used in the analyses. Call localization rates (CLRs) were compared before, during, and after periods of airgun use between sites near seismic activities (median distance 41–45 km) and sites relatively distant from seismic activities (median distance >104 km). At the onset of airgun use, CLRs dropped significantly at sites near the airguns, where median received levels from airgun pulses (SPL) were 116–129 dB re 1 μPa (10–450 Hz). CLRs remained unchanged at sites distant from the airguns, where median received levels were 99–108 dB re 1 μPa. This drop could result from a cessation of calling, deflection of whales around seismic activities, or both combined, but call locations alone were insufficient to differentiate between these possibilities. Reverberation from airgun pulses could have masked a small number of calls near the airguns, but even if masking did take place, the analysis results remain unchanged.

Modeling Propagation of Seismic Airgun Sounds and the Effects on Fish Behavior

High activity of seismic surveying in Norwegian waters has caused concerns about the impact the acoustic noise from the seismic airguns may have on marine life. There is evidence that this noise can cause reactions on the behavior of the fish resulting in reduced catches. To mitigate the problem and the conflict of interest between the fishing industry and the seismic exploration interest, the Norwegian Petroleum Directorate (NPD) commissioned SINTEF Information and Communication Technology (ICT, Trondheim, Norway) and the Department of Biology, University of Oslo (Oslo, Norway) to develop an acoustic-biological model to predict the impact of seismic noise on the fish population. The ultimate goal is to develop an acoustic-biological model to use in the design and planning of seismic surveys such that the disturbance to fishing interest is minimized. This acoustic module of the model is based on ray theory and can deal with range-dependent bathymetry and depth-dependent sound-speed profiles. The bottom is modeled as a sedimentary fluid layer over a solid elastic rock and the model requires the thickness and seismoacoustic properties of the sediments layer and the rock with compressional speed, shear speed, and absorption. The model simulates the total sound field, both in the time domain and in the frequency domain, out to very large distances. Calculated sound exposure levels are compared with startle response levels for cod. Preliminary conclusions indicate a required distance in the range of 5-10 km, but dependent on the depth and the season. In additions, under certain conditions, there will appear regions with hot spots where the sound level is significantly higher due to caustics and focusing of sound. Modeled results are compared with results obtained from a joint seismoacoustic survey conducted in summer 2009 at Vesterålen-Lofoten area (Nordland VII). In this experiment, signals were recorded at fixed hydrophone positions as the seismic vessel approached from a maximum distance of 30 km toward the receiving positions. The same situation was modeled using available geological and oceanographic information as input to the acoustic model. The agreement between the real and recorded signals and the model results is good. This indicates that in the future acoustic-biological models may be used in the design and planning of seismic surveys such that the disturbance to fishing is minimized.

High resolution data from DTAGS on the response of humpback whales to noise from seismic air guns

The BRAHSS (Behavioural Response of Australian Humpback Whales to Seismic Surveys) series of experiments uses a multi-platform approach to determine the behavioural and acoustic response of humpbacks to noise from seismic air gun arrays. One of the data collection platforms utilises the DTAG, or acoustic digital recording tag. DTAGs are small suction cup tags which contain a hydrophone as well as x, y and z plane accelerometers, magnetometers and depth sensors. Data from the DTAGs allows fine scale movement data of the tagged whale (dive profile, pitch, roll and heading movements, fluking rates) to be viewed as a pseudotrack whilst simultaneously listening to sound field of the whale (air gun shots and vocal sounds from nearby whales). This paper presents some results of responses of the whales to air gun sounds recorded by DTAGs and comparison with visual observations at the time. Since DTAGs provide a continuous record of whale vocalizations and 3D movements, vocal and physical reactions are detectable immediately as the first air gun shot occurs, whereas visual observation are limited to the appearance of the whales at the surface.

Sounds from airguns and fin whales recorded in the mid-Atlantic Ocean, 1999–2009

Between 1999 and 2009, autonomous hydrophones were deployed to monitor seismic activity from 16° N to 50° N along the Mid-Atlantic Ridge. These data were examined for airgun sounds produced during offshore surveys for oil and gas deposits, as well as the 20 Hz pulse sounds from fin whales, which may be masked by airgun noise. An automatic detection algorithm was used to identify airgun sound patterns, and fin whale calling levels were summarized via long-term spectral analysis. Both airgun and fin whale sounds were recorded at all sites. Fin whale calling rates were higher at sites north of 32° N, increased during the late summer and fall months at all sites, and peaked during the winter months, a time when airgun noise was often prevalent. Seismic survey vessels were acoustically located off the coasts of three major areas: Newfoundland, northeast Brazil, and Senegal and Mauritania in West Africa. In some cases, airgun sounds were recorded almost 4000 km from the survey vessel in areas that are likely occupied by fin whales, and at some locations airgun sounds were recorded more than 80% days/month for more than 12 consecutive months.

Effects of seismic exploration activities on bowhead whale call distribution in the Alaskan Beaufort Sea.

Airgun use during seismic exploration activities is known to cause a decrease in call detection rates (used here as a proxy for calling rates) in migrating bowhead whales. However, the received airgun sound levels at the whales, at which behavioral changes occur, are not known. To address this question 40 directional autonomous seafloor acoustic recorders (DASARs) were deployed in autumn 2008 at five sites along the migration corridor of bowhead whales during ongoing marine seismic exploration activities. Over 440 000 whale calls were detected and localized by triangulation. Concurrently, over 100 000 airgun pulses were detected and analyzed. The study area was divided into a hexagonal grid (hexagon width 1.75 km). The received level (SPL and cumulative SEL) of airgun sounds was modeled for each hexagon in the study area and each 15‐min period over the entire season, using information on the timing and location of airgun activities, the size of the airgun array being used, the depth of the DASARs recording the airgun sounds, and other covariates. Logistic regression was then used to model occurrence of whale calls as a function of received level, distance offshore, and other covariates. [Work supported by Shell Exploration and Production Company.]

Results and insights from operational acoustic monitoring networks in the Chukchi Sea, Summer‐Fall 2006 and 2008.

Recordings for marine mammals were collected in the Chukchi Sea in the 2006 and 2008 summer‐fall seasons in proximity to seismic exploration activities. 2006 data were from MARUs off Cape Lisburne, Pt. Lay, Wainwright, and Pt. Barrow, AK. 2008 data were from MARUs in the Burger and Klondike areas. In 2006, belugas, but no bowheads, were rarely detected off Cape Lisburne in July–September. Bowheads, but no belugas, were detected off Wainwright, Lay, and Barrow in September–October, with bowheads very common off Barrow. Seismic airgun sounds were common on distant MARUs off Cape Lisburne, Lay, and Wainwright. There were very few seismic events detected off Barrow and those few were all close to 0‐dB SNR. In 2008, bowheads were more common at Burger than Klondike and occurred mostly during the latter part of the September–October period; belugas were not detected at Burger and only on 6 days early in the period at Klondike; walrus were more common at Burger than at Klondike. In both areas bowhead densities were low‐moderate. Seismic sparker sounds were detected on 7 and 28 days at Burger and Klondike, respectively, with higher received levels at Klondike.

Seismic airgun sounds recorded in the North Atlantic.

Between 1999 and 2008, a consortium of international investigators deployed autonomous hydrophones to monitor seismic activity along the Mid‐Atlantic Ridge. Although this experiment was designed to monitor low‐frequency sounds from earthquakes, other natural and man‐made sounds were also recorded. The periodic impulses produced by airguns from exploration activities around the Atlantic basin were one of the dominant signals detected in this dataset. Sounds associated with seismic exploration, particularly sounds from airgun arrays, have garnered interest recently due to concerns regarding the potential impact on marine mammals. In a previous publication, we reported that in 1999–2001 airgun sounds were recorded year‐round on all hydrophones, but airgun activity peaked in the summer months. For this study, we used an automatic algorithm to detect airgun sounds in the 2001–2008 portion of the dataset. Raw detections were then visually examined by an experienced analyst to verify the accuracy of the detections. When airgun impulses were simultaneously recorded on four or more hydrophones, the location of the seismic exploration vessel was estimated. Results from this dataset will be presented in light of current knowledge of marine mammal distribution and migration patterns in the Atlantic.

Acoustic sampling for marine mammals in the Beaufort Sea July 2007–March 2008.

As climate change is driving rapid, unprecedented warming of the Arctic, there is increasing interest in how such change will impact Arctic marine mammals. Impacts are anticipated from from habitat alteration, including increasing ambient noise levels from shipping, seismic exploration for oil and gas and geophysical research, and (potentially) commercial fishing. In order to monitor natural and anthropogenic sources of noise, four autonomous recorders were deployed along the 100‐m isobath between Cape Halkett and Barrow and recorded data from July 2007–March 2008. The instruments sampled at 8192 Hz on a schedule of 10 min on, 20 min off. Marine mammal sounds recorded included pinnipeds (walrus and bearded seals) and cetaceans (bowhead and beluga whales), while anthropogenic sources included shipping and air gun sounds. Seasonal and geographic patterns for these sounds will be presented. These data form part of a broader‐scale international, year‐round monitoring program in the Arctic that we hope will ev...