Network Of Hydrophones Research Articles

Movement patterns and home ranges of a pelagic carangid fish, Caranx crysos, around a petroleum platform complex

Quantification of the movements and home ranges of highly mobile marine species is a challenging prerequisite for a more complete understanding of their ecology. Caranx crysos is a pelagic carangid found in large schools over the mid-shelf of the northern Gulf of Mexico. Twenty- three C. crysos were surgically implanted with acoustic transmitters, and their positions were local- ized around a petroleum platform complex in the Gulf of Mexico using a hydrophone network. Fish were tracked during August 2005 for 23 d, and home ranges were calculated for individual fish over the daily, diel, and entire study period. Most fish showed a preference for a discrete area within the platform complex: 11 fish had a range centroid near one platform for at least 7 d, and 9 fish had a range centroid near one platform for at least 3 d. Only 3 fish showed no preference for a particular site within the platform complex. Mean core daily range varied from 373 to 2202 m 2 , while the 95% daily range was between 3082 and 14 333 m 2 . Evidence for diel differences in habitat use was also apparent. Hydrophones detected more transmissions during the day than during the night; however, only 3 fish had significantly larger home ranges during the day than during the night. There was a significant correlation between fish length and both the size of their overall core home range and the size of the 95% daily home range. Our results suggest that this schooling pelagic species establishes a home range in the vicinity of structure.

January 2006 seafloor‐spreading event at 9°50′N, East Pacific Rise: Ridge dike intrusion and transform fault interactions from regional hydroacoustic data

An array of autonomous underwater hydrophones is used to investigate regional seismicity associated with the 22 January 2006 seafloor‐spreading event on the northern East Pacific Rise near 9°50′N. Significant earthquake activity was observed beginning 3 weeks prior to the eruption, where a total of 255 earthquakes were detected within the vicinity of the 9°50′N area. This was followed by a series of 252 events on 22 January and a rapid decline to background seismicity levels during the subsequent 3 days. Because of their small magnitudes, accurate locations could be derived for only 20 of these events, 18 of which occurred during a 1‐h period on 22 January. These earthquakes cluster near 9°45′N and 9°55′N, at the distal ends of the young lava flows identified posteruption, where the activity displays a distinct spatial‐temporal pattern, alternating from the north to the south and then back to the north. This implies either rapid bilateral propagation along the rift or the near‐simultaneous injection of melt vertically from the axial magma lens. Short‐duration T wave risetimes are consistent with the eruption of lavas in the vicinity of 9°50′N on 22 January 2006. Eruptions on 12 and 15–16 January also may be inferred from the risetime data; however, the locations of these smaller‐magnitude events cannot be determined accurately. Roughly 15 h after the last earthquakes were located adjacent to the eruption site, a sequence of 16 earthquakes began to the north‐northeast at a distance of 25–40 km from the 9°50′N site. These events are located in vicinity of the Clipperton Transform and its western inside corner, an area from which the regional hydrophone network routinely detects seismicity. Coulomb stress modeling indicates that a dike intrusion spanning the known eruptive zone to the south (9°46′–9°56′N) would act to promote normal faulting or a combination of normal faulting and transform slip within this region, with stress changes on the order of 1–10 kPa.

Killer whale habitat use and prey fields from remote hydrophones and echosounders.

The Salish Sea Hydrophone Network has been providing live audio streams to listeners around the globe for the past three years. Five hydrophones around the core summer habitat of the endangered southern resident killer whales allow detection of killer whale presence and inference of pod identity based on call associations. Detection of calls, whistles, and clicks is accomplished automatically by spectral and time domain analysis and manually by a global network of trained human listeners. The hydrophone network is more effective than a sighting network for detecting killer whales during inclement weather and at night, and for generating real‐time notifications to alert researchers and managers. Additionally, the live streams and archived recordings have enriched educational activities of local museums and aquariums. In 2008, the hydrophone at Lime Kiln State Park was supplemented by hydroacoustic surveys conducted using a Biosonics echosounder (200 kHz). From August through December the echosounder was deployed at 15 m depth to conduct a continuous, fixed, horizontal survey. Remote display technology was used to monitor the echosounder in real time while also listening to the live audio stream. The resultant time series of fish density and acoustic behavior of killer whales is presented.

Frequency quantiles and dual harmonic tracking for detection and classification of killer whale calls.

The Salish Sea Hydrophone Network, www.OrcaSound.net, is operating five streaming hydrophones in the critical habitat of the endangered Southern Resident orcas. Software is being developed that allows each site to sift through the approximately 10 Gbytes of information that are produced each day at each site in order to detect killer whale calls and related sounds. Detection of calls is accomplished via triggering on three time dependent features extracted in real‐time from sequential power spectra. One of these three features is derived from the bandwidth between quartiles of the filtered power spectrum. The other two quantify the degree to which the power spectrum has one or two harmonic structures. Features are extracted into feature sets that save the details of each feature: amplitudes; durations; and time variations. A metric has been devised that measures the similarity of different sequences of feature sets. With this metric an unsupervised learning algorithm builds a tree structure that classifies sounds by their similarity. As new calls come in, they either fall into pre‐existing groups or create new branches. Automatic reports are made via the Web and e‐mail.

Passive acoustic tomography: new concepts and applications using marine mammals: a review

This paper presents the new concept of passive acoustic tomography which allows ocean data collection with a passive acoustic remote sensing process. The originality lies in using acoustic sources of opportunity such as surface noise, radiated ship noise and marine mammal calls. Such use of passive tomography is a promising way to reduce acoustic emissions in oceans. A review is first presented, including the description of new concepts of covert active, assisted passive and autonomous tomography, followed by applications on real world data. Under the assumptions of multipath propagation and measurements performed by a sparse network of hydrophones, a time–frequency processor is proposed to simultaneously estimate the source location and the impulse response of the propagation channel for marine mammal calls used as opportunistic sources (multipath structure, time delay and attenuation are estimated). Promising results are obtained on real data coming from the Laurentian channel where wideband beluga calls (1 to 3 kHz) are measured by a sparse network of 6 bottom hydrophones.

Site fidelity and activity patterns of a humphead wrasse, Cheilinus undulatus (Labridae), as determined by acoustic telemetry

This study examines the short-term site fidelity, the home range size and the activity patterns of one specimen of the emblematic and threatened humphead wrasse, Chelinus undulatus. Four omnidirectional hydrophones were deployed for 7 months in the mooring area of Laregnere marine reserve (New Caledonia). The hydrophone network covered 50 ha. The monitored fish was caught in the study site and surgically implanted with an ultrasonic transmitter. The fish displayed a regular diurnal rhythm during 25 days before leaving the area. Different patterns of spatial use were identified. The temporal succession of these patterns indicates that the minimum distance covered by the fish every day ranged between 20 and 200 m. Its home range was at least 5 ha. A decrease of the detection was observed before the departure of the fish. This decrease coincided with the beginning of the reproduction period in New Caledonia and supports the hypothesis of a fish departure for the reproductive event. Despite the survey of only one specimen, the home range and movement calculated using acoustic telemetry are different in scale than the reported scuba-based visual estimations. Such information is essential for the development of management policies and conservation measures of large reef fish species highly vulnerable to disturbance and fishing pressure.

Hydroacoustic detection of volcanic ocean-island earthquakes

SUMMARY Real-time monitoring of volcanic earthquakes forms a critical component of assessing volcanic hazard but requires a widely dispersed land-based instrument network and analysis infrastructure to be effective. Here we show how a sparse network of hydrophones can be used for volcano monitoring as well. Detection of acoustic events by the Mid-Atlantic Ridge hydrophone array includes many events in the vicinity of the Cape Verde Islands, upon which a volcano monitoring network operates. Correlating the hydroacoustic events with earthquake locations determined by the network, we find that earthquakes of magnitudes as low as ML 2.0 can be hydroacoustically located to ±25 km at ranges up to 2000 km. All correlatable events are volcano-tectonic in character. Acoustic propagation of small-magnitude earthquake signals is more efficient if their sources are perched in the island’s volcanic edifice in the ocean sound transmission channel, which contributes to volcanic event detectability. The location accuracy at this low magnitude range, which includes magnitudes typical of seismic crises precursory to eruptions, provides an additional volcanic hazard monitoring capability. Seismicity and hydroacoustic activity in the northern Cape Verdes suggest that this monitoring element may be of use in assessing future risk there.

Vocal behavior of resident killer whale matrilines with newborn calves: The role of family signatures

Studies of the vocal behavior of resident killer whales or orcas, Orcinus orca, in British Columbia have shown that matrilines have unique call repertoires consisting of up to 17 different call types. These call types cannot be attributed exclusively to specific behaviors, and their function in social contexts is poorly understood. This study investigated the change in call patterns of three resident matrilines in a changed social environment, before and up to one year after the birth of a calf. Acoustic data were collected with a network of hydrophones and were supplemented by visual observations. Call use changed distinctly after the birth of a calf in all three observed matrilines. All call types that were recorded in control situations were also recorded in postbirth situations; however, aberrant versions of discrete calls and excitement calls made up a higher proportion of calls after birth. Most conspicuously, family-specific call types occurred significantly more frequently in the days following a birth in two of the three matrilines and gradually returned to prebirth values within 2 weeks. Their increased use after a calf's birth may facilitate the learning process of this "acoustic family badge" and thereby help to recognize and maintain cohesion with family members.

Testing low/very low frequency acoustic sources for basin-wide propagation in the Indian Ocean

Low/very low frequency acoustic signals were transmitted to distant receivers in the Indian Ocean. The aim was to test methods for characterizing the hydroacoustic capability of the International Monitoring System (IMS) that discriminates for nuclear tests in the region. Several acoustic sources were deployed between Seychelles and Fremantle, Australia, and the IMS receivers comprised a network of hydrophones off Diego Garcia and Australia. Two of the three acoustic sources tested produced basin-scale propagation of impulsive signals. Single glass spheres imploded within the sound channel produced a clear signal at frequencies above ∼40 Hz, at ranges of hundreds to a thousand kilometers. Five-sphere glass implosions were recorded at ranges up to 4400 km. Near-sea surface shots from a large airgun array were recorded in several cases at ranges of hundreds to thousands of kilometers, the frequency of the highest signal-to-noise ratio arrivals varied within the 5–100 Hz band. High background noise level was a key factor at IMS stations that did not detect the airgun signals in the 5–15 Hz band. In a few cases, details of bathymetric features that are not well represented in the digital elevation model contributed to unexpected variation in relative signal levels between IMS stations.

Automated model-based localization of marine mammals near Hawaii

Acoustic data from the Pacific Missile Range Facility (PMRF) hydrophone network near Hawaii is being used to develop a real-time automated alert and tracking algorithm. The sources of interest are marine mammals, humpback whales in particular, which are regularly seen in the vicinity of the PMRF array. The algorithm under development uses acoustic data from six hydrophones plus an acoustic propagation model to construct an ambiguity surface identifying the most probable whale location in a horial plane around the array. It has the further advantage that it can be implemented in real-time and without human interaction, making it suitable for automated alert applications.

Hydroacoustic detection of submarine landslides on Kilauea Volcano

Landslides produced at the site where lava flows into the ocean at Kilauea volcano have been detected hydroacoustically. Up to 10 landslides per day were detected by a hydrophone on the Hawaii Undersea Geo‐Observatory (HUGO), located 50 km south of the entry site. The largest of these landslides, partly subaerial events known as bench collapses, were detected by a network of hydrophones in the eastern Pacific, 5000–7000 km away from the source. The landslides display a characteristic spectral signature easily recognizable among other signals such as earthquake T‐phases and anthropogenic noises. The fact that signals are detected at great distances suggests that hydroacoustic detection of landslides could be a powerful tool in tsunami monitoring and modeling efforts.

Hydroacoustic monitoring of the oceans

In order to verify compliance with this Treaty, an international Monitoring System based on four technologies, seismology, infrasounds, hydroacoustic, and radionuclides, shall be implemented. Therefore, a network of hydrophones and seismic T-wave stations has been designed and evaluated in terms of detectability and location capability. Hydroacoustic waves generated by an undersea explosion or by oceanic earthquakes are propagating over several thousands of kilometers within an oceanic waveguide called So.F.A.R., channel (sound fixing and ranging) as shown by Ewing and Tolstoy (1950). When they are reaching any continental slope or island they are converted in seismic T-waves which are recorded by seismographs. By using both numerical simulations and experimental analysis, a methodology has developed which allows to better understand and quantify the effects of the source parameters and of the propagation characteristics (specifically on the So.F.A.R. channel and of the continental slope) on the recorded waveforms. The results obtained should be useful to improve the evaluation of detectability and location capability of the future hydroacoustic network and should provide some effective guidance to the site survey process. For that purpose and also to have a better understanding of the source parameters and of the acoustic wave propagation, a methodology has developed using both a numerical simulation and an experimental analysis.

Earthquake studies using under-ice hydrophone data (‘‘Spinnaker’’)

Preliminary studies indicate that the Spinnaker array, a network of hydrophones currently deployed in the Arctic Ocean, may be used to monitor seismicity of the Arctic Basin, as well as long distance teleseismic arrivals from the Southern Hemisphere. The Arctic Basin is a tectonically complex region that has seen few seismic studies, and the Spinnaker array has the potential to monitor some of its most interesting features, such as the Nansen–Gekkel Ridge (the slowest spreading ridge in the world), in near real time. In addition, teleseismic arrivals at the array may have raypaths that coincide closely with the Earth’s spin axis. These data may prove useful to current studies of the crystalline alignment and differential spin of the Earth’s inner core.

Relaxation techniques for finding horizontal eigenrays for global scale propagation

Prediction of the localization performance of a global hydrophone network requires the rapid computation of horizontal eigenrays connecting receivers to a grid of hypothetical source locations. The computation of these eigenrays using shooting techniques can be time consuming. For many of the paths, the refracted geodesic can be quite close to the horizontally refracted ray. In these cases relaxation techniques can be successfully used to bend the geodesic trial solutions onto the refracted path. This technique, which involves the iterative solution of a block diagonal system of equations, offers substantial performance benefits. Work by Collins et al. [J. Acoust. Soc. Am. 95, 3167–3170 (1994)] also suggests that relaxation techniques are useful for avoiding shooting problems associated with sensitivity to initial conditions, a common problem when shooting rays near shoaling bathymetry. Comparisons between traditional shooting eigenrays and the relaxed eigenrays are made and conclusions regarding the range of applicability of the relaxation technique are presented. [Work supported by DOE and Air Force Phillips Laboratory.]

Earthquake activity near Ascension Island, South Atlantic Ocean, as seen by a combined seismic/hydrophone array

Earthquake activity in the vicinity of Ascension Island is studied using data from a recently installed, very broadband seismographic station and a network of ocean hydrophones deployed around the island. The seismic station ASCN recorded 121 local earthquakes over a 188-day period. Distance from ASCN is computed for 41 of these events, most of which occurred at approximately 100 km—the distance to the Mid-Atlantic Ridge. A local magnitude scale is calibrated and applied to the same 41 events with mahnitudes ranging from 0.4 to 4.2. Six earthquakes were located using data from the hydrophones and ASCN. Two of the earthquakes occur on the Ascension Fracture Zone 35 km northwest of the island and the other four near the ridge-transform intersection. The locations have errors less than 10 km and frequently less than 3 km. There is no direct evidence for seismicity connected with geothermal activity on Ascension Island during the observation period.

Spectra and magnitudes of T‐waves from the 1993 earthquake swarm on the Juan de Fuca Ridge

A swarm of earthquakes on the crest of the Juan de Fuca Ridge was detected in June and July 1993 by a network of hydrophones. The activity migrated 60 km along the crest, suggesting a lateral dike injection and the possibility of a volcanic eruption. Subsequent geologic and oceanographic investigations confirmed that an eruption had taken place. Examination of the individual acoustic arrivals shows changes in the character of the signal that are consistent with an injection of magma. A reduction in the rise time of the wave packet and a proportional increase in high frequency energy was observed and is interpreted to result from a shoaling of the earthquake source region. Second, the source magnitudes were largest at the onset of the swarm and became smaller over time, also consistent with shoaling of the dike. The appearance of the T‐wave arrivals changed significantly 5 days after the beginning of the swarm, potentially indicating the onset of a surface eruption.

Earthquakes in the Orozco Transform Zone: Seismicity, source mechanisms, and tectonics

As part of the Rivera Ocean Seismic Experiment, a network of ocean bottom seismometers and hydrophones was deployed in order to determine the seismic characteristics of the Orozco transform fault in the central eastern Pacific. We present hypocentral locations and source mechanisms for 70 earthquakes recorded by this network. All epicenters are within the transform region of the Orozco Fracture Zone and clearly delineate the active plate boundary. About half of the epicenters define a narrow line of activity parallel to the spreading direction and situated along a deep topographic trough that forms the northern boundary of the transform zone (region 1). Most focal depths for these events are very shallow, within 4 km of the seafloor; several well‐determined focal depths, however, are as great as 7 km. No shallowing of seismic activity is observed as the rise‐transform intersection is approached; to the contrary, the deepest events are within 10 km of the intersection. First motion polarities for most of the earthquakes in region 1 are compatible with right‐lateral strike slip faulting along a nearly vertical plane, striking parallel to the spreading direction. Another zone of activity is observed in the central part of the transform (region 2). The apparent horizontal and vertical distribution of activity in this region is more scattered than in the first, and the first motion radiation patterns of these events do not appear to be compatible with any known fault mechanism. Pronounced lateral variations in crustal velocity structure are indicated for the transform region from refraction data and measurements of wave propagation directions. The effect of this lateral heterogeneity on hypocenters and fault plane solutions is evaluated by tracing rays through a three‐dimensional velocity grid. While findings for events in region 1 are not significantly affected, in region 2, epicentral mislocations of up to 10 km and azimuthal deflections of up to 45° may result from assuming a laterally homogeneous velocity structure. When corrected for the effects of lateral heterogeneity, the epicenters and fault plane solutions for earthquakes in region 2 are compatible with predominantly normal faulting along a topographic trough trending NW–SE; the focal depths, however, are poorly constrained. These results suggest an en echelon spreading center or leaky transform regime in the central transform region.

Submarine volcanic eruptions recently located in the Pacific by Sofar Hydrophones

Abstract : Five sources of underwater sound having volcanic characteristics have been located in the Pacific Ocean by means of the Pacific Missile Range sofar hydrophone network. Two are in the Mariana Islands, one in the Nanpo Shoto, one in the Aleutian Islands, and one at the southeast end of the Austral Seamounts. The sounds range in duration from a few seconds (explosive) to weeks (periodic low rumblings). Sonagrams of some of these events show multiple bands as do those of underwater explosions.

Routine location of T-phase sources in the Pacific

abstract A program for the routine location of T-phase sources in the Pacific is described. Data for this program are supplied principally by the Pacific Missile Range hydrophone network. Arrival times and power levels are read at Honolulu for processing by an IBM 7040 computer. The solution for location and origin time is the least-squares fit to all hydrophone arrivals which are weighted according to their distribution in azimuth and their distance from the T-phase source. The velocities for the program are obtained from algebraic functions of latitude and longitude which are based upon shot calibrations and upon hydrographic measurements. A T-phase strength is computed from readings of peak power level in a manner analogous to earthquake magnitude. Early results for the r.m.s. difference between T-phase source locations and the corresponding earthquake epicenters were 0.6° in the Aleutians and 1.1° in the Kuril Islands.