David M. Farmer

Zones of impact around icebreakers affecting beluga whales in the Beaufort Sea.

A software model estimating zones of impact on marine mammals around man-made noise [C. Erbe and D. M. Farmer, J. Acoust. Soc. Am. 108, 1327-1331 (2000)] is applied to the case of icebreakers affecting beluga whales in the Beaufort Sea. Two types of noise emitted by the Canadian Coast Guard icebreaker Henry Larsen are analyzed: bubbler system noise and propeller cavitation noise. Effects on beluga whales are modeled both in a deep-water environment and a near-shore environment. The model estimates that the Henry Larsen is audible to beluga whales over ranges of 35-78 km, depending on location. The zone of behavioral disturbance is only slightly smaller. Masking of beluga communication signals is predicted within 14-71-km range. Temporary hearing damage can occur if a beluga stays within 1-4 km of the Henry Larsen for at least 20 min. Bubbler noise impacts over the short ranges quoted; propeller cavitation noise accounts for all the long-range effects. Serious problems can arise in heavily industrialized areas where animals are exposed to ongoing noise and where anthropogenic noise from a variety of sources adds up.

Masked hearing thresholds of a beluga whale (Delphinapterus leucas) in icebreaker noise

Abstract An experiment is presented that measured masked hearing thresholds of a beluga whale at the Vancouver Aquarium. The masked signal was a typical beluga vocalization; the masking noise included two types of icebreaker noise and naturally occurring icecracking noise. Thresholds were measured behaviorally in a go/no-go paradigm. Results were that bubbler system noise exhibited the strongest masking effect with a critical noise-to-signal ratio of 15.4xa0dB. Propeller cavitation noise completely masked the vocalization for noise-to-signal ratios greater than 18.0xa0dB. Natural icecracking noise showed the least interference with a threshold at 29.0xa0dB. A psychophysical analysis indicated that the whale did not have a consistent decision bias.

A software model to estimate zones of impact on marine mammals around anthropogenic noise

Anthropogenic noise impacts marine mammals in a variety of ways. In order to estimate over which ranges this happens, we first need to understand the propagation of noise through the ocean away from the noise source, and, second, understand the relationship between received noise levels and impact thresholds. A software package combining both aspects is presented. (1) A sound propagation model based on ray theory was developed to calculate received noise levels as a function of range, depth, and frequency. (2) Current knowledge of noise impact thresholds for marine mammals was gathered and included in software routines predicting zones of impact on marine mammals around industrial underwater noise sources. As input parameters, this software package requires the source level and spectrum of the noise of interest; physical oceanography data about the local ocean environment such as bathymetry, bottom and surface loss data, and sound speed profiles; and bioacoustical information about the target species in the form of an audiogram, critical auditory bandwidths, spectra of typical animal vocalizations, reported sound levels of disturbance, and criteria for hearing damage. As output, the software produces data files and plots of the zones of audibility, masking, disturbance, and potential hearing damage around a noise source.

Ocean flow measurements using acoustic scintillation

A wave propagating in a medium having random fluctuations in refractive index will suffer phase and amplitude perturbations. In the receiving plane, a random interference pattern will appear and this so‐called scintillation pattern will vary in time for two reasons: (1) the decay of the refractive‐index fluctuations producing the amplitude perturbation (eddy decay) and (2) advection of the eddies by the flow. In the case where eddy lifetimes are long compared with the scintillation period, we can derive estimates of flow from a statistical analysis of the scintillation pattern. In this paper, we discuss the propagation theory and report measurements of oceanic flows by analysis of the acoustic scintillation pattern produced by the density fluctuations in the ocean. By mounting a 214‐kHz source and two receivers on opposite sides of a barge such that the axis of propagation is perpendicular to the direction of travel, we induce a known flow rate equal to the barge velocity. We compute the slope of the time...

Computer models for masked hearing experiments with beluga whales (Delphinapterus leucas)

Environmental assessments of manmade noise and its effects on marine mammals need to address the question of how noise interferes with animal vocalizations. Seeking the answer with animal experiments is very time consuming, costly, and often infeasible. This article examines the possibility of estimating results with software models. A matched filter, spectrogram cross-correlation, critical band cross-correlation, and a back-propagation neural network detected a beluga vocalization in three types of ocean noise. Performance was compared to masked hearing experiments with a beluga whale [C. Erbe and D. M. Farmer, Deep-Sea Res. II 45, 1373-1388 (1998)]. The artificial neural network simulated the animal data most closely and raised confidence in its ability to predict the interference of a variety of noise source with a variety of vocalizations.

Broadband parametric imaging of breaking ocean waves

An acoustic array was deployed in the near-surface layer of a fetch-limited coastal inlet to image breaking waves using only the sound radiated in the band (400 Hz to 2000 Hz) from the breaking region. The breakers were assumed to possess predominantly spiller characteristics. For this frequency band, the wavelength of sound in bubble-free water is much larger than the surface wave height and the depth of the breaker bubble plume, so both were considered insignificant. The 15-element array was configured as a sparse horizontal cross with an 8 m aperture, bottom moored, and positioned nominally 3 m beneath the surface. Propagation from the source to the array elements assumed dipole sources, an acoustically flat surface, and an acoustically thin bubble plume. The radiating region was parameterized by a broadband two-dimensional Gaussian profile: information from up to six independent frequencies was combined to yield a maximum-likelihood image. Analysis shows that the images align closely with the wind and...

Development of a software package calculating zones of influence on marine mammals around industrial noise sources

A software package is presented which estimates zones of interference around underwater noise sources affecting marine mammals. An ocean sound propagation model based on ray theory computes the spreading of complex underwater sound such as broadband animal vocalizations and man‐made noise. On a grid of receiver locations (representing the affected marine mammal), the received signal and noise sound spectra are compared. Given a species‐specific audiogram, the software package plots zones of audibility around the noise source. Given species‐specific vocalizations, zones of masking are plotted based on results obtained during an earlier study which measured masked hearing thresholds of a beluga vocalization in icebreaker noise with a trained beluga whale. Tools developed during this study (such as an artificial neural network and critical band methods) are incorporated in the software package and can be used to predict zones of masking for industrial noise other than the types directly measured with the bel...

A software package calculating zones of impact on marine mammals around industrial noise sources

A software package is presented which estimates zones of interference around underwater noise sources affecting marine mammals. An ocean sound propagation model based on ray theory computes the spreading of complex underwater sound such as broadband animal vocalizations and manmade noise. On a grid of receiver locations (representing the affected marine mammal), the received signal and noise sound spectra are compared. Given a species‐specific audiogram, the software package plots zones of audibility around the noise source. Given species‐specific vocalizations, zones of masking are plotted based on results obtained during an earlier study which measured masked hearing thresholds of a beluga whale. Tools developed during this study (such as an artificial neural network model to predict the amount of masking) can be linked to the software package. Zones of behavioral disturbance are plotted based on received sound levels reported in the literature. Zones of discomfort, injury, and hearing loss could be plo...

Auditory masking of whale communication by ship noise

A method is presented to determine the acoustic masking effects of man‐made noise on marine mammal communication. In particular, the interference of icebreaker related noise with beluga whale vocalizations is studied. Captive beluga whales have been trained for acoustic experiments during which they try to detect beluga vocalizations in various noisy backgrounds. In a stop/go manner, the animals indicate whether or not they can discriminate call from noise. Results are that bubbler system noise, generated when an icebreaker ejects high pressure air into the sea in order to push ice debris away, has the worst masking effects followed by propeller cavitation noise, generated when an icebreaker is stopped by an iceridge. Naturally occurring thermal icecracking noise has the least masking impact. Based on the experimentally collected data, computer software was developed to model the whale’s auditory abilities. Means of adaptive noise cancellation greatly outperform the whale and are hence not considered to t...