Three-dimensional localization of sperm whales using a single hydrophone.
06 Oct 2006-Journal of the Acoustical Society of America (Acoustical Society of America)-Vol. 120, Iss: 4, pp 2355-2365
TL;DR: Three tracks of whale activity using real data from one or two hydrophones have been created, and three are provided to demonstrate the method, including one simultaneous visual and acoustic localization of a sperm whale actively clicking while surfaced.
Abstract: A three-dimensional localization method for tracking sperm whales with as few as one sensor is demonstrated. Based on ray-trace acoustic propagation modeling, the technique exploits multipath arrival information from recorded sperm whale clicks and can account for waveguide propagation physics like interaction with range-dependent bathymetry and ray refraction. It also does not require ray identification (i.e., direct, surface reflected) while utilizing individual ray arrival information, simplifying automation efforts. The algorithm compares the arrival pattern from a sperm whale click to range-, depth-, and azimuth-dependent modeled arrival patterns in order to estimate whale location. With sufficient knowledge of azimuthally dependent bathymetry, a three-dimensional track of whale motion can be obtained using data from a single hydrophone. Tracking is demonstrated using data from acoustic recorders attached to fishing anchor lines off southeast Alaska as part of efforts to study sperm whale depredation...
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01 Apr 2011Abstract: Acknowledgements Introduction Part I. Underwater Acoustics (The Basics): 1. Principles of underwater sound 2. Cetacean sounds 3. Sonar equation Part II. Signal Processing (Designing the Tools): 4. Detection methods 5. Classification methods 6. Localisation and tracking Part III. Passive Acoustic Monitoring (Putting It All Together): 7. Applications of PAM 8. Detection functions 9. Simulating sampling strategies 10. PAM systems 11. References and literature Index.
135 citations
TL;DR: Ratilal et al. as discussed by the authors used a combination of passive and active ocean acoustic waveguide remote sensing in an important northwestern Atlantic marine mammal autumn foraging ground to detect, localize and classify MM vocalizations from diverse species over an approximately 100,000 km2 region.
Abstract: Vocalizations were recorded for over eight distinct whale species as they converged on a shoal of herring to feed; the predators divided the shoal into overlapping but species-specific foraging sectors and the activities of the whales changed between day and night. Using a combination of passive and active ocean acoustic waveguide remote sensing in an important northwestern Atlantic marine mammal autumn foraging ground, Purnima Ratilal and colleagues have mapped the movement and distribution of more than ten marine mammal species simultaneously with that of their fish prey. The vocalizations of humpback, blue, fin, minke and other marine mammal species were recorded across an area of roughly 100,000 square kilometres as they converged onto dense herring shoals, dividing them into overlapping but species-specific foraging sectors, which were maintained for more than two weeks. This snapshot of marine life reveals how predators moved through the huge shoal, indicating how the activities of the predators varied as day moved into night. The results will increase understanding of marine-mammal behaviour and inform conservation efforts. Observing marine mammal (MM) populations continuously in time and space over the immense ocean areas they inhabit is challenging but essential for gathering an unambiguous record of their distribution, as well as understanding their behaviour and interaction with prey species1,2,3,4,5,6. Here we use passive ocean acoustic waveguide remote sensing (POAWRS)7,8 in an important North Atlantic feeding ground9,10 to instantaneously detect, localize and classify MM vocalizations from diverse species over an approximately 100,000 km2 region. More than eight species of vocal MMs are found to spatially converge on fish spawning areas containing massive densely populated herring shoals at night-time11,12,13,14,15,16 and diffuse herring distributions during daytime. We find the vocal MMs divide the enormous fish prey field into species-specific foraging areas with varying degrees of spatial overlap, maintained for at least two weeks of the herring spawning period. The recorded vocalization rates are diel (24 h)-dependent for all MM species, with some significantly more vocal at night and others more vocal during the day. The four key baleen whale species of the region: fin, humpback, blue and minke have vocalization rate trends that are highly correlated to trends in fish shoaling density and to each other over the diel cycle. These results reveal the temporospatial dynamics of combined multi-species MM foraging activities in the vicinity of an extensive fish prey field that forms a massive ecological hotspot, and would be unattainable with conventional methodologies. Understanding MM behaviour and distributions is essential for management of marine ecosystems and for accessing anthropogenic impacts on these protected marine species1,2,3,4,5,17,18.
54 citations
TL;DR: Experimental results using pseudorandom signals show that accurate localization results are achieved by offline iteration of the extended Kalman filter.
Abstract: Localizing a source of radial movement at moderate range using a single hydrophone can be achieved in the reliable acoustic path by tracking the time delays between the direct and surface-reflected arrivals (D-SR time delays). The problem is defined as a joint estimation of the depth, initial range, and speed of the source, which are the state parameters for the extended Kalman filter (EKF). The D-SR time delays extracted from the autocorrelation functions are the measurements for the EKF. Experimental results using pseudorandom signals show that accurate localization results are achieved by offline iteration of the EKF.
53 citations
TL;DR: Timing and tracking analyses of sperm whale acoustic activity during three encounters indicate that cavitation arising from changes in ship propeller speeds is associated with interruptions in nearby sperm whale dive cycles and changes in acoustically derived positions.
Abstract: Sperm whales (Physeter macrocephalus) have learned to remove fish from demersal longline gear deployments off the eastern Gulf of Alaska, and are often observed to arrive at a site after a haul begins, suggesting a response to potential acoustic cues like fishing-gear strum, hydraulic winch tones, and propeller cavitation. Passive acoustic recorders attached to anchorlines have permitted continuous monitoring of the ambient noise environment before and during fishing hauls. Timing and tracking analyses of sperm whale acoustic activity during three encounters indicate that cavitation arising from changes in ship propeller speeds is associated with interruptions in nearby sperm whale dive cycles and changes in acoustically derived positions. This conclusion has been tested by cycling a vessel engine and noting the arrival of whales by the vessel, even when the vessel is not next to fishing gear. No evidence of response from activation of ship hydraulics or fishing gear strum has been found to date.
44 citations
TL;DR: The first attempt to use multi-year passive acoustic data to study the impact of the Deepwater Horizon oil spill on the population of endangered sperm whales is reported, with a comparison of the 2007 and the 2010 recordings shows a decrease in acoustic activity and abundance of sperm whales at the 9-mile site by a factor of 2, whereas acoustic activity
Abstract: Long-term monitoring of endangered species abundance based on acoustic recordings has not yet been pursued. This paper reports the first attempt to use multi-year passive acoustic data to study the impact of the Deepwater Horizon oil spill on the population of endangered sperm whales. Prior to the spill the Littoral Acoustic Demonstration Center (LADC) collected acoustic recordings near the spill site in 2007. These baseline data now provide a unique opportunity to better understand how the oil spill affected marine mammals in the Gulf of Mexico. In September 2010, LADC redeployed recording buoys at previously used locations 9, 25, and 50 miles away from the incident site. A statistical methodology that provides point and interval estimates of the abundance of the sperm whale population at the two nearest sites is presented. A comparison of the 2007 and the 2010 recordings shows a decrease in acoustic activity and abundance of sperm whales at the 9-mile site by a factor of 2, whereas acoustic activity and abundance at the 25-mile site has clearly increased. This indicates that some sperm whales may have relocated farther away from the spill. Follow-up experiments will be important for understanding long-term impact.
43 citations
References
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TL;DR: Geoacoustic models of the sea floor are basic to underwater acoustics and to marine geological and geophysical studies of the earth's crust, including stratigraphy, sedimentology, geomorphology, structural and gravity studies, geologic history, and many others as mentioned in this paper.
Abstract: Geoacoustic models of the sea floor are basic to underwater acoustics and to marine geological and geophysical studies of the earth’s crust, including stratigraphy, sedimentology, geomorphology, structural and gravity studies, geologic history, and many others A ’’geoacoustic model’’ is defined as a model of the real sea floor with emphasis on measured, extrapolated, and predicted values of those properties important in underwater acoustics and those aspects of geophysics involving sound transmission In general, a geoacoustic model details the true thicknesses and properties of sediment and rock layers in the sea floor A complete model includes water‐mass data, a detailed bathymetric chart, and profiles of the sea floor (to obtain relief and slopes) At higher sound frequencies, the investigator may be interested in only the first few meters or tens of meters of sediments At lower frequencies information must be provided on the whole sediment column and on properties of the underlying rocks Complete geoacoustic models are especially important to the acoustician studying sound interactions with the sea floor in several critical aspects: they guide theoretical studies, help reconcile experiments at sea with theory, and aid in predicting the effects of the sea floor on sound propagation The information required for a complete geoacoustic model should include the following for each sediment and rock layer In some cases, the state‐of‐the‐art allows only rough estimates, in others information may be nonexistent (1) Identification of sediment and rock types at the sea floor and in the underlying layers (2) True thicknesses and shapes of layers, and locations of significant reflectors (which may vary with sound frequencies) For the following properties, information is required in the surface of the sea floor, in the surface of the acoustic basement, and values of the property as a function of depth in the sea floor (3) Compressional wave (sound) velocity (4) Shear wave velocity (5) Attenuation of compressional waves (6) Attenuation of shear waves (7) Density (8) Additional elastic properties (eg, dynamic rigidity and Lame’s constant); given compressional and shear wave velocities and density, these and other elastic properties can be computed There is an almost infinite variety of geoacoustic models; consequently, the floor of the world’s ocean cannot be defined by any single model or even a small number of models; therefore, it is important that acoustic and geophysical experiments at sea be supported by a particular model, or models, of the area However, it is possible to use geological and geophysical judgement to extrapolate models over wider areas within geomorphic provinces To extrapolate models requires water‐mass data (such as from Nansen casts and velocimeter lowerings), good bathymetric charts, sediment and rock information from charts, cores, and the Deep Sea Drilling Project, echo‐sounder profiles, reflection and refraction records (which show detailed and general layering and the location of the acoustic basement), sound velocities in the layers, and geological and geophysical judgement Recent studies have provided much new information which, with older data, yield general values and restrictive parameters for many properties of marine sediments and rocks These general values and parameters, and methods for their derivation, are the main subjects of this paper
885 citations
TL;DR: The Gaussian beam method as mentioned in this paper associates with each ray a beam with a Gaussian intensity profile normal to the ray, and the beamwidth and curvature are governed by an additional pair of differential equations, which are integrated along with the usual ray equations to compute the beam field.
Abstract: The method of Gaussian beam tracing has recently received a great deal of attention in the seismological community. In comparison to standard ray tracing, the method has the advantage of being free of certain ray‐tracing artifacts such as perfect shadows and infinitely high energy at caustics. It also obviates the need for eigenray computations. The technique is especially attractive for high‐frequency, range‐dependent problems where normal mode, FFP, or parabolic models are not practical alternatives. The Gaussian beam method associates with each ray a beam with a Gaussian intensity profile normal to the ray. The beamwidth and curvature are governed by an additional pair of differential equations, which are integrated along with the usual ray equations to compute the beam field in the vicinity of the central ray of the beam. We have adapted the beam‐tracing method to the typical ocean acoustic problem of a point source in a cylindrically symmetric waveguide with depth‐dependent sound speed. We present an overview of the method and a comparison of results obtained by conventional ray‐tracing, beam‐tracing, and full‐wave theories. These results suggest that beam tracing is markedly superior to conventional ray tracing.
454 citations
TL;DR: In this paper, the authors estimate the abundance of sperm whales in a 7.8 million km 2 study area in the eastern temperate North Pacific using data from a ship-based acoustic and visual line-transect survey in spring 1997.
Abstract: We estimate the abundance of sperm whales in a 7.8 million km 2 study area in the eastern temperate North Pacific using data from a ship-based acoustic and visual line-transect survey in spring 1997. Sperm whales were detected acoustically using a hydrophone array towed at 15 km/h and 100 m depth. The hydrophone array was towed for 14,500 km, and locations were estimated acoustically for 45 distinct sperm whale groups. Whales producing slow clicks (.2-s period) were detected at greater distance (up to 37 km), and the estimation of effective strip widths was stratified based on initial click period. Visual survey effort (using 253 binoculars and naked eyes) covered 8,100 km in Beaufort sea states 0‐5 and resulted in only eight sightings. The effective strip width for visual detections was estimated from previous surveys conducted using the same methods and similar vessels in the eastern Pacific. Estimated sperm whale abundance in the study area was not significantly different between acoustic (32,100, CV ¼0.36) and visual (26,300, CV ¼0.81) detection methods. Acoustic techniques substantially increased the number of sperm whales detected on this line-transect survey by increasing the range of detection and allowing nighttime surveys; however, visual observations were necessary for estimating group size.
241 citations
TL;DR: Whales glides more during portions of dives when buoyancy aided their movement, and whales that glided more during ascent glided less during descent (and vice versa), supporting the hypothesis that buoyancy influences behavioural swimming decisions.
Abstract: SUMMARY Drag and buoyancy are two primary external forces acting on diving marine
mammals. The strength of these forces modulates the energetic cost of movement
and may influence swimming style (gait). Here we use a high-resolution digital
tag to record depth, 3-D orientation, and sounds heard and produced by 23
deep-diving sperm whales in the Ligurian Sea and Gulf of Mexico. Periods of
active thrusting versus gliding were identified through analysis of
oscillations measured by a 3-axis accelerometer. Accelerations during 382
ascent glides of five whales (which made two or more steep ascents and for
which we obtained a measurement of length) were strongly affected by depth and
speed at Reynold9s numbers of 1.4–2.8×107. The
accelerations fit a model of drag, air buoyancy and tissue buoyancy forces
with an r2 of 99.1–99.8% for each whale. The model
provided estimates (mean ± s.d.) of the drag coefficient
(0.00306±0.00015), air carried from the surface (26.4±3.9 l
kg-3 mass), and tissue density (1030±0.8 kg m-3)
of these five animals. The model predicts strong positive buoyancy forces in
the top 100 m of the water column, decreasing to near neutral buoyancy at
250–850 m. Mean descent speeds (1.45±0.19 m s-1) were
slower than ascent speeds (1.63±0.22 m s-1), even though
sperm whales stroked steadily (glides 5.3±6.3%) throughout descents and
employed predominantly stroke-and-glide swimming (glides 37.7±16.4%)
during ascents. Whales glided more during portions of dives when buoyancy
aided their movement, and whales that glided more during ascent glided less
during descent (and vice versa), supporting the hypothesis that
buoyancy influences behavioural swimming decisions. One whale rested at∼
10 m depth for more than 10 min without fluking, regulating its buoyancy
by releasing air bubbles.
228 citations
TL;DR: Previously published properties of sperm whale clicks underestimate the capabilities of the sound generator and therefore cannot falsify the Norris and Harvey theory.
Abstract: In sperm whales (Physeter catodon L. 1758) the nose is vastly hypertrophied, accounting for about one-third of the length or weight of an adult male. Norris and Harvey [in Animal Orientation and Navigation, NASA SP-262 (1972), pp. 397–417] ascribed a sound-generating function to this organ complex. A sound generator weighing upward of 10 tons and with a cross-section of 1 m is expected to generate high-intensity, directional sounds. This prediction from the Norris and Harvey theory is not supported by published data for sperm whale clicks (source levels of 180 dB re 1 μPa and little, if any, directionality). Either the theory is not borne out or the data is not representative for the capabilities of the sound-generating mechanism. To increase the amount of relevant data, a five-hydrophone array, suspended from three platforms separated by 1 km and linked by radio, was deployed at the slope of the continental shelf off Andenes, Norway, in the summers of 1997 and 1998. With this system, source levels up to 223 dB re 1 μPa peRMS were recorded. Also, source level differences of 35 dB for the same click at different directions were seen, which are interpreted as evidence for high directionality. This implicates sonar as a possible function of the clicks. Thus, previously published properties of sperm whale clicks underestimate the capabilities of the sound generator and therefore cannot falsify the Norris and Harvey theory.
220 citations