David R Barclay

Dalhousie University | Dal · Department of Oceanography

A quasi-analytical three-dimensional (3D) normal mode model for longitudinally invariant environments can be used to compute vertical noise coherence in idealized ocean environments. An examination of the cross modal amplitudes in the modal decomposition of the noise cross-spectral density shows that the computation can be simplified, without loss...

A slowdown in global trade activity due to COVID-19 has led to a reduction in commercial shipping traffic into the Port of Vancouver. The Ocean Networks Canada observatory system provides researchers real-time access to oceanographic data from a wide range of instruments including hydrophones located along the offshore and inshore approaches to Van...

The ambient sound field in the ocean can be decomposed into a linear combination of two independent fields attributable to wind-generated wave action at the surface and noise radiated by ships. The vertical coherence (the cross-spectrum normalized by the power spectra) and normalized directionality of wind-generated noise in the ocean are stationar...

Since HMS Challenger made the first sounding in the Mariana Trench in 1875, scientists and explorers have been seeking to establish the exact location and depth of the deepest part of the ocean. The scientific consensus is that the deepest depth is situated in the Challenger Deep, an abyss in the Mariana Trench with depths greater than 10,000 m. Si...

An ocean-ice-acoustic coupled model is configured for the Beaufort Sea. The model uses outputs from a data assimilating global scale ice-ocean-atmosphere forecast to drive a bimodal roughness algorithm for generating a realistic ice canopy. The resulting range-dependent ice cover obeys observed roughness, keel number density, depth, and slope, and...

A four-element three-dimensional hydrophone array has been deployed on the Strait of Georgia node of the Victoria Experimental Network Under the Sea (VENUS) since March 2020. To the present, continuous pressure time series data from the four sensors has been streamed ashore and made available by Ocean Networks Canada. A technique for classifying an...

Data time series covering extended periods of time in support of long-term environmental studies are particularly difficult and expensive to collect, especially at offshore locations. Ocean Networks Canada’s (ONC) undersea cabled observatories in the Northeast Pacific ocean have been collecting an extensive array of oceanographic, seismic, geophysi...

A two-month-long glider deployment in the Gulf of St. Lawrence, Canada, measured the ambient sound level variability with depth and lateral position across a narrow channel that serves as an active commercial shipping corridor. The Honguedo Strait between the Gaspé Peninsula and Anticosti Island has a characteristic sound channel during the Summer...

Citation: Troup, M.L.; Hatcher, M.; Barclay, D. Creating an Autonomous Hovercraft for Bathymetric Surveying in Extremely Shallow Water (<1 m). Sensors 2023, 23, 7375. Abstract: Coastal shallow water environments (<5 m) are extremely biodiverse and dynamic yet are often mapped too infrequently or at too low resolutions to capture the important proce...

Modern techniques for hydrophone calibration from IEC 60565:2020 typically require sensors to be placed in a free field or within a hydrostatically varying chamber. At mid-frequencies (defined as 1 kHz–10 kHz), the wavelength is too long for free-field conditions in tanks available to most manufacturers and academics. A novel technique to calibrate...

Encoded in the spectral density, spatial variability, and directionality (spatial coherence) of the ambient sound field is information on the generation mechanisms of sound and the properties of the ocean propagation environment and its boundaries. Through field and observatory measurements, and analytical and computational models of the underwater...

The performance of a hydrophone array can be evaluated by its coherent gain, which depends on the spatial correlation of both the signal of interest and the background noise between different array elements, where one hopes to maximize the former while minimizing the latter with array signal processing. In this paper, a computational vertical noise...

To evaluate the performance of underwater acoustic communication systems, it is typically assumed that the noise at the receiver is uncorrelated spatially and temporally. This assumption underestimates the impact of acoustic ocean ambient noise on the performance of communication systems. In this article, the impact of ocean ambient noise on a cohe...

No PDF available ABSTRACT As part of the Sustainable Nunatsiavut Futures project, a field experiment to determine the acoustic properties and underwater radiated sound level of a snowmobile was designed and executed. The fieldwork consists of lowering acoustic recorders under the sea ice and driving a snowmobile with a known position and velocity t...

No PDF available ABSTRACT Hydrothermal vents are sea floor structures where geothermally heated seawater is discharged. The high-temperature, chemically rich environment is host to uniquely adapted marine life. Vent soundscapes may contain important bioacoustic cues as well as signals enabling passive acoustic monitoring of hydrothermal vent dynami...

No PDF available ABSTRACT A 48-hydrophone bottom-mounted array in the Arctic provides an opportunity to test a novel acoustic frequency tracker on ships of opportunity. The Arctic is is currently experiencing an historic increase in shipping traffic, resulting in an acoustic environmental that is changing rapidly. Through the ice-free study period,...

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

No PDF available ABSTRACT An eight-element drifting vertical line array was deployed overwinter 2019–20 in the Beaufort Sea to record transmissions from two moored 35 Hz sources deployed as part of the Coordinated Arctic Acoustic Thermometry Experiment (CAATEX), and seven 925 Hz sources deployed by the Arctic Mobile Observing Systems (AMOS) experim...

No PDF available ABSTRACT Ambient noise in the Arctic exhibits significant spatial, temporal and spectral variability. This poses significant challenges for passive sonar performance estimation since the probability of detection is measured against this noise background. This is exacerbated by the relative paucity of measurements made in this remot...

The main sources of noise in the Arctic Ocean are naturally occurring, rather than related to human activities. Sustained acoustic monitoring at high latitudes provides quantitative measures of changes in the sound field attributable to evolving human activity or shifting environmental conditions. A 12-month ambient sound time series (September 201...

Anthropogenic underwater noise has been identified as a potentially serious stressor for the critically endangered North Atlantic right whale (NARW). The Government of Canada is undertaking steps to better characterize the noise sources of most concern and their associated impacts, but there is currently an insufficient understanding of which noise...

No PDF available ABSTRACT An acoustic recorder was deployed near the Port of Sept-Îles, Quebec in the fall of 2020 and collected six months of data on a four-channel orthogonal array. The system, a JASCO C-lander, operated on a duty cycle consisting of 340s of data recorded at 32 kHz sampling rate, 1 min of data recorded at 256 kHz sampling rate fo...

No PDF available ABSTRACT The sounds of the turning machinery and propulsion systems from commercial ships are ubiquitous in the temperate deep ocean basins. The vertical structure of seawater temperature, salinity, and pressure conspire to create nearly lossless underwater propagation conditions at 10’s and 100’s of Hz, the frequency band where di...

No PDF available ABSTRACT Passive acoustics may provide a method for detection and long-term monitoring of hydrothermal vents. Direct measurement of vent activity can be challenging as vent plumes are often high temperature (i>300°C) and acidic. The discovery of new vent sites can also be challenging as detection of vent plumes or high-resolution s...

No PDF available ABSTRACT Echo sounding and acoustic propagation in the hadal zone (depths below 6 km) rely on models of sound speed that suffer from uncertainty due to a paucity of measurements at those depths. In order to assess models of sound speed in deep water, and to provide additional measurements, the Deep Acoustic Lander, a passive acoust...

Reliable and power efficient underwater communication systems that can adapt to the mediums changing nature can be designed with knowledge of the physical underwater environment. This paper discusses a stochastic model for an underwater acoustic channel that takes into consideration the effects of flow and turbulence on the acoustic signal in envir...

Quantifying changes in ambient-noise levels is an important component of characterizing marine soundscapes. Starting from January 2020, the economic slowdown due to the COVID-19 pandemic, coupled with an oil-price war, has offered a rare opportunity to observe significant variations in anthropogenic marine ambient noise on a relatively short time s...

The Arctic has been a refuge from anthropogenic underwater noise; however, climate change has caused summer sea ice to diminish, allowing for unprecedented access and the potential for increased underwater noise. Baseline underwater sound levels must be quantified to monitor future changes and manage underwater noise in the Arctic. We analyzed 39 p...

No PDF available ABSTRACT A slowdown in global trade activity due to COVID-19 has led to a reduction in commercial shipping traffic into the Port of Vancouver. The Ocean Networks Canada observatory system provides researchers real-time access to oceanographic data from a wide range of instruments including hydrophones located along the offshore and...

No PDF available ABSTRACT The Barrow Straight Real-time Observatory is a cabled underwater monitoring station operated by Fisheries and Oceans Canada in the Tallurutiup Imanga National Marine Conservation Area. The observatory measures temperature, salinity, pressure, dissolved oxygen, currents, ambient noise and ice draft. Every 2 h a hydrophone r...

The Royal Canadian Airforce (RCAF) is proud of its well-deserved reputation for environmental stewardship. With the advent of in-service low-frequency active sonar sources the RCAF is reviewing and updating policies and procedures to limit the potential impacts of active sonar on whales. During active sonar activities, passive sonar sonobuoys can b...

No PDF available ABSTRACT Scientists and explorers have been searching to determine the exact location and depth of the deepest part of the ocean since the HMS Challenger made the first sounding of the Mariana Trench in 1875. The consensus is that the deepest abyss in the ocean is in the Challenger Deep, a portion of the Mariana Trench with depths...

NOTE: This is the abstract of a conference presentation. There is no article. I have uploaded the video of the presentation as a supplemental file here. In the Arctic, sound levels have historically been strongly tied to sea ice and wind speed, with very little impact of anthropogenic noise. However, climate change is causing a loss of sea ice, an...

In this paper, the communication quality of an underwater acoustic link between two nodes is quantified by the predicted channel gain and delay spread using a stochastic and reinforcement learning model. The stochastic model generates an ensemble of time-varying channel characteristics by capturing the effect of known environmental changes includin...

Numerous studies of ocean ambient noise and under-ice acoustic propagation and reverberation in the Canadian Arctic have been carried out since the 1960s. These studies, largely led by scientists at the Defence Research Establishment Pacific and Defence Research and Development Canada, have been motivated by the need to improve sonar performance pr...

This article analyzes the effects of key physical oceanographic conditions on underwater propagation in a shallow water environment. Signals at 2 kHz were transmitted and received over ranges of 1–10 km, and the variability in the sound-speed profile, bathymetry, position of the instruments, and sea surface roughness was measured and the uncertaint...

Regulations designed to mitigate the effects of man-made sounds on marine mammal hearing specify maximum daily sound exposure levels. The limits are lower for impulsive than non-impulsive sounds. The regulations do not indicate how to quantify impulsiveness; instead sounds are grouped by properties at the source. To address this gap, three metrics...

Baseline ambient sound level assessment is important in quantifying anthropogenic noise contributions. Static acoustical sensing in high-flow conditions is complicated by pseudosound, or flow noise, caused by turbulent flow on the surface of a hydrophone. Signal processing methods are used to identify and suppress flow noise at low frequencies ( $<...

No PDF available ABSTRACT During the period of 2005–2011, three topics in acoustical oceanography were actively investigated in the Buckingham Lab which combined field, lab, and theoretical work. Geoacoustic inversions in the low frequency (<500 Hz) band were carried out using the noise generated by a light aircraft off the coast of La Jolla, Calif...

No PDF available ABSTRACT Ambient noise data collected on a pair of omni-directional vertically separated hydrophones at the head of Alvin Canyon, a shelf-break submarine canyon, is used to estimate the range and bearing of a passing vessel. Comparison of the vertical coherence data against a Pekeris normal-mode model may be used to provide the ran...

No PDF available ABSTRACT A horizontal hydrophone array is typically beamformed to produce the directivity required to produce array gain and determine bearing to a contact of interest. For ships passing near an array each omnidirectional hydrophone also provides a number of discrete “look windows” at the ship from a range of received angles. By as...

No PDF available ABSTRACT The objective of this work is to model the natural ambient noise level in coastal regions based on local environmental forcing and propagation conditions. 546 continuous hours of noise were recorded between April 15 and May 7, 2018 in Sooke Inlet, British Columbia, a coastal, shallow-water region with complex bathymetry an...

No PDF available ABSTRACT Underwater communications and sonar measurements in the Arctic are challenging due to the remoteness and the vast area to be covered. Acoustic modeling is critical to support measurements since it can help inform experimental plans and extend the usefulness of results to other areas. Low-frequency systems are generally req...

The autonomous passive-acoustic lander Deep Sound was deployed at five locations during the Office of Naval Research (ONR)-supported Seabed Characterization Experiment, a multi-institutional field effort held at the New England Mud Patch, where the seabed is known to consist of a thick layer of silt and clay overlying a medium and coarse sand. The...

Acoustic recordings were made during the installation of four offshore wind turbines at the Block Island Wind Farm, Rhode Island, USA. The turbine foundations have four legs inclined inward in a pyramidal configuration. Four bottom mounted acoustic recorders measured received sound levels at distances of 541–9067 m during 24 pile driving events. Li...

The absorption of sound in seawater is due to the viscous and chemical relaxation of different compounds. Over the wind noise band of 1–10 kHz, the frequency dependence of the absorption is due to the mechanisms of chemical relaxation for magnesium sulfate (f > 3 kHz) and for boric acid (f < 3 kHz), which involve ionic dissociations activated and d...

During the Seabed Characterization Experiment, a multi-institutional field effort held at the New England mud patch, the autonomous passive acoustic lander Deep Sound made a series of ambient noise measurements from the seafloor. The instrument platform carried four hydrophones, arranged in an inverted ‘T’ shape with three spaced in the horizontal...

Underwater acoustic processes including ambient noise, propagation, reverberation, and scattering have been studied for over half a century in the Canadian Arctic. Despite this, realistic predictions of communications and sonar performance have proved challenging due to the complex impact of ice cover on these processes, and the relative scarcity o...

The Arctic is a region known for high variance in both ambient noise levels and local sound propagation conditions, and is currently experiencing an historic increase in shipping traffic, resulting in an acoustic environmental that is changing so rapidly that the sparse ambient noise data available from decades-old studies have been rendered obsole...

This paper develops a linearized Bayesian inversion algorithm for high-precision localization of an autonomous underwater vehicle (AUV) on a test range using time difference of arrival acoustic data. The Bayesian approach allows the uncertainties of several factors, including precise receiver locations and bias and lateral variability of the water-...

Continuous ambient noise data were recorded during April and May 2016, using a four-element vertical array deployed near the continental shelf break south of Martha’s Vineyard. A technique for classifying and partitioning ambient noise using the vertical noise coherence function is proposed. Time series analysis of the noise power spectrum reveals...

The ambient sound field due to wind generated surface noise and distant ship generated noise may be highly axially non-symmetric in regions with rapidly changing bathymetry. Some of this asymmetry is due to bathymetric shadowing, while in other cases horizontal refraction contributes significantly. These propagation effects can alter the omnidirect...

Metrics such as the acoustic complexity index, acoustic diversity index, entropy, evenness, and roughness have been correlated with anthropogenic and biologic sound sources in terrestrial soundscapes. The metrics offer the possibility of characterizing the presence of sound sources and the biodiversity of an environment in large datasets without ha...

The autonomous passive acoustic lander Deep Sound was deployed five times during the Seabed Characterization Experiment and collected ambient noise data on four hydrophones, arranged in a inverted “T” shape, with three spaced in the horizontal and two in the vertical. The lander was deployed with the bottom-most phones approximately 30 cm above the...

No PDF available ABSTRACT Pairs of hydrophones were buried at mid-tide height in a 1:10 sloped mixed gravel and coarse sand beach and used to make ambient noise recordings over a period of three weeks in Advocate Harbour, Nova Scotia, in the Bay of Fundy. The pairs were arranged in vertical and horizontal configurations and recorded pressure time s...

A series of experiments aimed at measuring the power spectrum and vertical and horizontal noise coherence (directionality) in the deep ocean were carried out between 2009and 2015 using a family of autonomous instrument platforms named “Deep Sound.” Deep Sound is a free-falling acoustic recorder designed to descend from the ocean’s surface to a pre-...

The marine environment in the Bay of Fundy hosts a dynamic and diverse soundscape that is a fundamental component of the local ecosystem. The emergence of new human marine activities and infrastructure, such as tidal turbine installations, introduces new sound sources that change or disrupt the existing acoustic environment, but the full extent of...

Commonly used air-side remote sensing techniques (e.g., cameras,GPS, wireless communications, and radar) are not suitable for many oceanographic applications because seawater is opaque to electromagnetic radiation. Acoustic signals, on the other hand, propagate relatively well underwater and can be used for remote sensing, imaging, and communicatio...

The Ocean Tracking Network operates and maintains a continental shelf scale array of 256 bottom mounted fish-tag monitoring stations, spanning from the entrance of Halifax harbour to the Scotian Shelf break. These stations detect tagged keystone, commercially important, and endangered species as they migrate across this acoustic curtain, known as t...

The ambient sound field due to wind generate surface noise in an idealized Gaussian submarine canyon can be described using the method of normal mode decomposition applied to a three-dimensional longitudinally invariant wave-guide. The modal decomposition is carried out in the vertical and across-canyon horizontal directions and gives a semi-analyt...

In September 2012, the free-falling, deep-diving instrument platform Deep Sound III descended to the bottom of the Tonga Trench, where it resided at a depth of 8515 m for almost 3 h, recording ambient noise data on four hydrophones arranged in a vertical L-shaped configuration. The time series from each of the hydrophones yielded the power spectrum...

Underwater sound propagation on slopes and canyons is influenced jointly and strongly by the complexity of topographic variability and ocean dynamics. Some integrated ocean and acoustic models have been developed and implemented to investigate such joint acoustic effects. In this talk, an integrated numerical model employing a time-stepping three-d...

A prototype wideband coherent Doppler profiler (MFDop) was tested for measuring bedload velocity of different gravel and coarse-sand-sized fractions (d = 1-32 mm) in the laboratory. The sediment was spread out on a smooth-surface tray, and motion was initiated by tilting the tray at angles of alpha = 20 degrees-39 degrees from the horizontal. Parti...

An efficient numerical calculation of the vertical and horizontal coherence of the noise field in the ocean due to a distributed sheet of sources can be carried out using a parabolic equation (PE) propagation model and the reciprocity property of the complex pressure field. In the case of an infinite sheet of sources near the surface in an infinite...

During the Philippine Sea experiment in May 2009, Deep Sound, a free-falling instrument platform, descended to a depth of 5.1 km and then returned to the surface. Two vertically aligned hydrophones monitored the ambient noise continuously throughout the descent and ascent. A heavy rainstorm passed over the area during the deployment, the noise from...

In May of 2012, three weeks of ambient noise measurements from a hydrophone buried 30 cm deep in the sediment were recorded at Advocate Beach, a 1:10 sloped beach at the head of the Bay of Fundy, Nova Scotia. While tides varied the mean water depth between 0 and 4 m, 0.8 m surface waves passed overhead, driving sediment bedload transport and creati...

Most measurements of ambient noise in the deep ocean have been performed using an array of hydrophones located at a fixed depth. Recently, an instrument platform known as Deep Sound has been developed, consisting of a glass sphere containing data acquisition, data storage, and system control electronics, with a pair of vertically aligned hydrophone...

In 2009, as part of PhilSea09, the instrument platform known as Deep Sound was deployed in the Philippine Sea, descending under gravity to a depth of 6000 m, where it released a drop weight, allowing buoyancy to return it to the surface. On the descent and ascent, at a speed of 0.6 m/s, Deep Sound continuously recorded broadband ambient noise on tw...

DeepSound is an autonomous, high?bandwidth acoustic recording system designed to profile ambient noise to depths of 9 km. Recent ambient noise measurements recorded by the DeepSound probe well below the conjugate depth of the channel exhibit significant non?Gaussianity (the hypothesis of Gaussianity is rejected for 97% of 5 s samples using the larg...

Deep Sound is an un-tethered, free-falling acoustic platform designed to profile the ambient noise field in the ocean from the surface to a pre-programmed depth, at which point a ballast weight is dropped and the instrument returns to the surface under its own buoyancy. Three iterations of the instrument, Mk I, II and III, have been designed, built...

In November 2009, ambient noise measurements were made in the Mariana Trench from the surface to a depth of 9000 m using the instrument platform Deep Sound. Deep Sound is a free-falling acoustic recorder designed to descend from the ocean's surface to a pre-assigned depth where it drops an iron weight and returns to the surface under its own buoyan...

Deep Sound is an untethered instrument platform designed to free-fall from the sea surface to a preassigned depth, at which point a burn wire releases a weight, allowing the system to return to the surface under buoyancy. The descent and ascent rate is 0.6 ms. A Vitrovex glass sphere houses lithium-ion batteries and a suite of microprocessor-contro...

Ambient noise in the deep ocean is traditionally monitored using bottom-mounted or surface-suspended hydrophone arrays. An alternative approach has recently been developed in which an autonomous, untethered instrument platform free falls under gravity from the surface to a preassigned depth, where a drop weight is released, allowing the system to r...

Digitized outlines of sand grains from a dozen locations have been acquired using an optical microscope. A Fourier decomposition of the outline is calculated providing a spectral description of the grain's shape. By averaging over several hundred grains, the normalized power spectrum of each sand sample is returned. The desert sands, beach sands, a...

Digitized outlines of sand grains from a dozen locations, including deserts, beaches, and seabeds, have been acquired using an optical microscope linked to a desktop computer. Fourier analysis of the outlines returns the normalized power spectrum of each sample, averaged over several hundred grains. Regardless of the origin of the samples, these po...

Deep Sound is a free-falling high-bandwidth acoustic recording system designed to profile ambient noise from the surface to depths of 9 km. The recording platform is autonomous and descends under gravity to its preprogramed maximum depth, where a burn-wire releases weight, permitting the system to return to the surface under its own buoyancy. Two h...

Characterization of a soundscape through objective parameters relies on our understanding of psychoacoustics and ability to model the complex signal processing of the mind. Certain physical parameters such as loudness and timbre are easily retrieved from data while other descriptive parameters are more difficult to measure objectively. Several sign...

Using data collected during the 2005 Makai experiment, acoustic parameters of a coral-sand seabed were obtained using the Doppler spectroscopy inversion technique. A light aircraft was used as a low frequency (80 - 400 Hz) sound source over an isovelocity shallow water channel. A microphone near the ocean surface and a hydrophone near the seabed we...

The porosity of marine sediments increases as the mean grain diameter decreases. In contrast, the close‐packing structures (including random packing) of uniform‐size spheres all show a porosity that is independent of sphere size. Hamilton suggested that, in sediments, the shape of the grains is instrumental in determining the porosity. To investiga...

In September 2005, during the Makai experiments off Kauai, a light aircraft acted as a moving sound source over a shallow‐ocean channel with a coral‐sand bottom. Core samples yielded the porosity, bulk density, grain density, and grain size of the sediment. Acoustic sensors (a microphone in the air and a line of hydrophones in the isovelocity water...

Traditional integrating spheres, which use a single detector to measure luminous flux, have a number of drawbacks associated with the sources of error caused by baffling, nonideal topology, and variations in surface reflectance. In this article we address the potential drawbacks of many traditional integrating spheres and present a new instrument w...

We report on the first measurements of infrared spectra of 6:2 FTOH. The measurements were taken using a 25-cm-path cell at room temperature over the spectral range 900-3500 cm-1. Our results reveal 6:2 FTOH as a potentially important greenhouse gas.