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GERVAISE, C., A. BARAZZUTTI, S. BUSSON, Y. SIMARD, N. ROY, 2010. Automatic detection of bioacoustics impulses based on kurtosis under weak signal to noise ratio. Applied acoustics, 71(11): 1020-1026 .
Passive acoustic monitoring (PAM) of marine mammal vocalizations has been efficiently used in a wide set of applications ranging from marine wildlife surveys to risk mitigation of military sonar emissions. The primary use of PAM is for detecting bioemissions, a good proportion of which are impulse sounds or clicks. A click detection algorithm based on kurtosis estimation is proposed as a general automatic click detector. The detector works under the assumption that click trains are embedded in stochastic but Gaussian noise. Under this assumption, kurtosis is used as a statistical test for detection. The algorithm explores acoustic sequences with the optimal frequency bandwidth for focusing on impulse sounds. The detector is successfully applied to field observations, and operates under weak signal to noise ratios and in presence of stochastic background noise. The algorithm adapts to varying click center frequency. Kurtosis appears as a promising approach to detect click trains, alone or in combination with other clicks detector, and to isolate individual clicks.©2010 Elsevier Ltd
Roy, N., Y. SIMARD, C. GERVAISE, 2010. 3D tracking of foraging belugas from their clicks : experiment from a coastal hydrophone array. Applied acoustics, 71: 1050-1056 .
A simple passive acoustic monitoring (PAM) setup was used to localize and track beluga whales underwater in three dimensions (3D) in a fjord. In June 2009, beluga clicks were recorded from a cabled hydrophone array in a regularly frequented habitat in Eastern Canada. Beluga click energy was concentrated in the 30–50 kHz frequency band. The click trains detected on several hydrophones were localized from their time difference of arrivals. Cluster analysis linked localizations into tracks based on criteria of spatial and temporal proximity. At close ranges from the array, the localized click-train series allowed three-dimensional tracking of a beluga during its dive. Clicks within a train spanned a large range of durations, inter-click intervals, source levels and bandwidths. Buzzes sometimes terminated the trains. Repeated click packets were frequent. All click characteristics are consistent with oblique observations from the beam axis, and ordered variation of the source pattern during a train, likely resulting from a scan of angles from the beam axis, was observed before click trains indicated focusing of the echolocation clicks in one direction. The click-train series is interpreted as echolocation chasing for preys during a foraging dive. Results show that a simple PAM system can be configured to passively and effectively 3D track wild belugas and small odontocetes in their regularly frequented habitat.©2010 Elsevier Ltd.
SIMARD, Y., N. ROY, S. GIARD, C. GERVAISE, M. CONVERSANO, N. MÉNARD, 2010. Estimating whale density from their whistling activity : example with St. Lawrence beluga. Applied acoustics, 71: 1081-1086 .
A passive acoustic method is developed to estimate whale density from their calling activity in a monitored area. The algorithm is applied to a loquacious species, the white whale (Delphinapterus leucas), in Saguenay fjord mouth near Tadoussac, Canada, which is severely affected by shipping noise. Beluga calls were recorded from cabled coastal hydrophones deployed in the basin while the animal density was estimated visually from systematic observations from a fixed-point on the shore. Beluga calling activity was estimated from an algorithm extracting the call events in time–frequency space, while simultaneously tracking the masking intensity resulting from local shipping noise. The activity index was summarized in 15- and 30-min bins using four different metrics. For bins containing more than 40 % of valid data, the metrics were compared to the corresponding visual observations. The estimated mean acoustic detection range generally exceeded the fjord width, and extended to the whole 3-km long monitored area under low-noise conditions. The significant linear relations of the visual estimates with the calling activity metrics allowed assessing expected number of visually detected belugas in the basin from a weighted regression model, with a mean standard error of 7.1. %. Crown copyright ©2010 Elsevier Ltd.
SIMARD Y., N. ROY, 2008. Detection and localization of blue and fin whales from large-aperture autonomous hydrophone arrays: a case study from the St.Lawrence estuary. Can. Acoust., 36(1): 104-110 .
The feasibility of using passive acoustic methods (PAM) to monitor time-space distribution of fin and blue whales in the Saguenay-St. Lawrence Marine Park was explored using large-aperture sparse hydrophone arrays. The arrays were deployed during summers 2003 to 2005 at the head of the 300-m deep Laurentian Channel. They were composed of 5 AURAL autonomous hydrophones moored at mid-water depths, near the summer sound channel. A small coastal array complemented the deployment in 2003. The apertures were from 20 to 40 km and the configurations were changed from year to year. The most frequent calls recorded were blue and fin whale signature infrasounds. Noise from transiting ships on the busy St. Lawrence Seaway often masked the calls on the nearest hydrophones. Sometimes this resulted in an insufficient number of receivers for localizing the whales using time difference of arrival (TDoA) methods. The technical characteristics of the arrays and data processing are presented, with an example of call detection and localization. Despite the difficulties inherent to this environment, PAM can be effectively implemented there, eventually for real-time operations.©2008 Canadian Acoustical Association
ROY, N., Y. SIMARD, J. ROUAT, 2008. Performance of three acoustical methods for localizing whales in the Saguenay - St. Lawrence Marine Park. Can. Acoust., 36(1): 160-164 .
Three algorithms are explored to localize fin whale calls recorded from a large-aperture hydrophone array deployed in the Saguenay - St. Lawrence Marine Park. The methods have to cope with varying sound speed in space and time, errors in time differences of arrival (TDoA) measurements in a noisy environment, and often a limited number of hydrophones having recorded a particular event. The array was composed of 5 AURAL autonomous hydrophones with a total aperture of about 40 km, coupled with 2 hydrophones from a small-aperture cabled coastal array. The autonomous hydrophones clock drifts were estimated with a level of uncertainty from timed sources and the coastal array time reference. The calls were then localized by constant-speed hyperbolic fixing, variable-speed isodiachron Monte-Carlo simulations, and a ray-tracing propagation model. The Monte-Carlo simulations generate clouds of possible localizations from the uncertainty in hydrophone positions, TDoAs and the effective horizontal sound speeds along the different source-hydrophone paths. The ray-tracing model produces a fixed grid of TDoAs which can then be consulted to find the likeliest positions of the whales. Results from the different methods are compared and their relative advantages or limitations are discussed.©2008 Canadian Acoustical Association
SIMARD, Y., N. ROY, C. GERVAISE, 2008. Passive acoustic detection and localization of whales: Effects of shipping noise in Saguenay-St. Lawrence Marine Park. J. Acoust. Soc. Am., 123(6): 4109-4117 .
The performance of large-aperture hydrophone arrays to detect and localize blue and fin whales' 15-85 Hz signature vocalizations under ocean noise conditions was assessed through simulations from a normal mode propagation model combined to noise statistics from 15960 h of recordings in Saguenay-St. Lawrence Marine Park. The probability density functions of 2482 summer noise level estimates in the call bands were used to attach a probability of detection/masking to the simulated call levels as a function of whale depth and range for typical environmental conditions. Results indicate that call detection was modulated by the calling depth relative to the sound channel axis and by modal constructive and destructive interferences with range. Masking of loud infrasounds could reach 40 % at 30 km for a receiver at the optimal depth. The 30 dB weaker blue whale D-call were subject to severe masking. Mapping the percentages of detection and localization allowed assessing the performance of a six-hydrophone array under mean- and low-noise conditions. This approach is helpful for optimizing hydrophone configuration in implementing passive acoustic monitoring arrays and building their detection function for whale density assessment, as an alternative to or in combination with the traditional undersampling visual methods.©2008 Acoustical Society of America
SIMARD, Y., M. BAHOURA, C.W. PARK, J. ROUAT, M. SIROIS, X. MOUY, D. SEEBARUTH, N. ROY, R. LEPAGE, 2006. Development and experimentation of a satellite buoy network for real-time acoustic localization of whales in the St. Lawrence. 6 pages in Oceans 2006 MTS/IEEE, Boston revolutionizing marine science and technology, Boston, Massachusetts, September 18-21, 2006 .
An integrated system of intelligent acoustic buoys have been developed to detect, identify and localize whales in real-time in their environment and communicate this information to land-based stations or ships via satellite and Internet, and RF communications. The low-cost portable buoy network can be used as a marine mammal observatory to gather continuous space-time series of vocalizing animals over large basins, or as early warning systems for improving whale protection on navigation routes or around moving or fixed platforms during threatening high-level acoustic activity. The unit buoy is powered by two 12-V batteries connected to solar panels. The processor is an 800 MHz Pentium III PC equipped with 400-MB fast memory and a 100-GB hard disk. The clock is synchronized with the embarked GPS. Data from two georeferenced hydrophones equipped with depth and temperature sensors are flowing to a 16-bit 500-kHz A/D-DSP board. Two-way communication is through 900-MHz and an Iridium satellite modems. Specific whales target calls are detected in time-frequency domain after adaptive noise-filtration. The selected master buoy collects the precisely time-tagged detections from all units via RF communication, and locates the calling whales from hyperbolic and isodiachron-Monte Carlo fixing algorithms. A simple tracking algorithm then builds the individual tracks. All acoustic data or users' selected portions of them can be stored on the hard disk. The system is designed to accommodate future developments and be easily adapted to various tasks. It can be deployed as a drifting network or anchored to the bottom, as well as from the ice sheet. First sea trials will be in August 2006 in the St. Lawrence.©2006 IEEE
SIMARD, Y., N. ROY, C. GERVAISE, 2006. Shipping noise and whales : world tallest ocean liner vs largest animal on earth. 6 pages in Oceans 2006 MTS/IEEE, Boston revolutionizing marine science and technology, Boston, Massachusetts, September 18-21, 2006 .
The noise spectra radiated by the world tallest ocean liner, the Queen Mary II (QM2), when she sailed over the blue whale feeding ground of the Saguenay—St. Lawrence Marine Park in Sept. And Oct. 2004 are presented. Recordings for her 4 transits were made from an array of AURAL autonomous hydrophones moored at mid water depth along the navigation corridor at the head of the Laurentian channel. Typical ship noise Lloyd's mirror patterns on spectrogram generally allowed identification of the closest points of approach (CPA) to the hydrophones. The analysis of the Doppler shift of stable QM2 spectral rays allowed estimating CPA ranges and sailing speed. QM2 noise signature is characterized by several strong rays between ˜100 to 500 Hz, likely from her propulsion pods. Her average noise spectra are however enclosed within the envelope of the merchant ship noise measured in the area, except for high peaks below 40 Hz and the above rays. Broadband (10-1000 Hz) rms levels varied from 121 to 136 dB re 1μPa. As for most other merchant ships, this radiated shipping noise makes a barrier masking the low-frequency vocalizations of calling blue and fin whales over a large part of the basin.©2006 IEEE
SIMARD, Y., M. BAHOURA, N. ROY, 2004. Acoustic detection and localization of whales in Bay of Fundy and St. Lawrence estuary critical habitats. Can. Acoust., 32(2): 107-116 .
The detection and localization of marine mammals using passive acoustics is explored for two critical habitats in Eastern Canada. Two-dimensional hyperbolic localization is performed on time differences of arrivals of specific calls on grids of coarsely spaced autonomous recorders and on a shore-linked coastal array of closely spaced hydrophones. Delays are computed from cross-correlation and spectrogram cross-coincidence on signals enhanced with high-frequency emphasis and noise spectral suppression techniques. The outcomes and relative performance of the two delay estimation methods are compared. The difficulties encountered under the particular conditions of these two environments are discussed for the point of view of automated localisation for monitoring whales.©2004 Canadian Acoustical Association
GILBERT, D., A.F. VÉZINA, B. PETTIGREW, D.P. SWAIN, P.S. GALBRAITH, L. DEVINE, N. ROY, 1997. État du golfe du Saint-Laurent : conditions océanographiques en 1995. Rapp. tech. can. hydrogr. sci. océan., 191, 113 p .
We present an overview of the oceanographic conditions in the Gulf of St. Lawrence for 1995. The highlights are that 1) winter air temperatures were near normal in the western Gulf, but were close to 2 °C below normal in the eastern Gulf; 2) the summer was warm and dry in the western Gulf; 3) the ice cover was slightly above normal, with more severe ice conditions in the northeastern Gulf than in the western Gulf; 4) the core temperature of the cold intermediate layer was colder than normal; 5) the bottom area with a temperature below 0 °C reached a record high in the southern Gulf; 6) the deep layers cooled relative to 1994, and the cooling was more intense in he 100-200 m layer (O.9 °C) than in the 200-300m layer (0.3 °C); 7) the dissolved oxygen content of the 200-300 m layer was slightly below the 1981-1995 average in the Cabot Strait and Honguedo Strait sections; 8) the distribution of chlorophyll and nitrate in the surface layer corresponded roughly with the patterns inferred from historical data, i.e. a gradient of decreasing biomass from the West and south towards the east and north that is strongly inversely correlated with salinity; 9) in Northumberland Strait, the concentrations of chlorophyll near the bottom were much higher than elsewhere.
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