scholarly journals A method for tracking blue whales (Balaenoptera musculus) with a widely spaced network of ocean bottom seismometers

PLoS ONE ◽  
2021 ◽  
Vol 16 (12) ◽  
pp. e0260273
Author(s):  
William S. D. Wilcock ◽  
Rose S. Hilmo
Keyword(s):  
Pacific Northwest ◽  
Marine Mammals ◽  
Likelihood Function ◽  
Double Difference ◽  
Ocean Bottom ◽  
Large Network ◽  
Ocean Bottom Seismometer ◽  
Balaenoptera Musculus ◽  
Ocean Bottom Seismometers ◽  
Blue Whales

Passive acoustic monitoring is an important tool for studying marine mammals. Ocean bottom seismometer networks provide data sets of opportunity for studying blue whales (Balaenoptera musculus) which vocalize extensively at seismic frequencies. We describe methods to localize calls and obtain tracks using the B call of northeast Pacific blue whale recorded by a large network of widely spaced ocean bottom seismometers off the coast of the Pacific Northwest. The first harmonic of the B call at ~15 Hz is detected using spectrogram cross-correlation. The seasonality of calls, inferred from a dataset of calls identified by an analyst, is used to estimate the probability that detections are true positives as a function of the strength of the detection. Because the spacing of seismometers reaches 70 km, faint detections with a significant probability of being false positives must be considered in multi-station localizations. Calls are located by maximizing a likelihood function which considers each strong detection in turn as the earliest arrival time and seeks to fit the times of detections that follow within a feasible time and distance window. An alternative procedure seeks solutions based on the detections that maximize their sum after weighting by detection strength and proximity. Both approaches lead to many spurious solutions that can mix detections from different B calls and include false detections including misidentified A calls. Tracks that are reliable can be obtained iteratively by assigning detections to localizations that are grouped in space and time, and requiring groups of at least 20 locations. Smooth paths are fit to tracks by including constraints that minimize changes in speed and direction while fitting the locations to their uncertainties or applying the double difference relocation method. The reliability of localizations for future experiments might be improved by increasing sampling rates and detecting harmonics of the B call.

Comparison of the S/N ratios of low-frequency hydrophones and geophones as a function of ocean depth

1981 ◽  
Vol 71 (5) ◽  
pp. 1649-1659
Author(s):  
Thomas M. Brocher ◽  
Brian T. Iwatake ◽  
Joseph F. Gettrust ◽  
George H. Sutton ◽  
L. Neil Frazer
Keyword(s):  
Nova Scotia ◽  
Continental Margin ◽  
Low Frequency ◽  
Weather Conditions ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Scotian Shelf ◽  
Ocean Bottom Seismometers ◽  
Particle Velocities ◽  
Refraction Data

abstract The pressures and particle velocities of sediment-borne signals were recorded over a 9-day period by an array of telemetered ocean-bottom seismometers positioned on the continental margin off Nova Scotia. The telemetered ocean-bottom seismometer packages, which appear to have been very well coupled to the sediments, contained three orthogonal geophones and a hydrophone. The bandwidth of all sensors was 1 to 30 Hz. Analysis of the refraction data shows that the vertical geophones have the best S/N ratio for the sediment-borne signals at all recording depths (67, 140, and 1301 m) and nearly all ranges. The S/N ratio increases with increasing sensor depth for equivalent weather conditions. Stoneley and Love waves detected on the Scotian shelf (67-m depth) are efficient modes for the propagation of noise.

Development of a Compact Broadband Ocean-Bottom Seismometer

2021 ◽  
Author(s):  
Masanao Shinohara ◽  
Tomoaki Yamada ◽  
Hajime Shiobara ◽  
Yusuke Yamashita
Keyword(s):  
Low Frequency ◽  
Plate Boundaries ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Broadband Seismometer ◽  
Seismic Sensors ◽  
Slow Earthquakes ◽  
Short Period ◽  
Ocean Bottom Seismometers

Abstract Studies of very-low-frequency earthquakes and low-frequency tremors (slow earthquakes) in the shallow region of plate boundaries need seafloor broadband seismic observations. Because it is expected that seafloor spatially high-density monitoring requires numerous broadband sensors for slow earthquakes near trenches, we have developed a long-term compact broadband ocean-bottom seismometer (CBBOBS) by upgrading the long-term short-period ocean-bottom seismometer that has seismic sensors with a natural frequency of 1 Hz and is being mainly used for observation of microearthquakes. Because many long-term ocean-bottom seismometers with short-period sensors are available, we can increase the number of broadband seafloor sensors at a low cost. A short-period seismometer is exchanged for a compact broadband seismometer with a period of 20 or 120 s. Because the ocean-bottom seismometers are installed by free fall, we have no attitude control during an installation. Therefore, we have developed a new leveling system for compact broadband seismic sensors. This new leveling system keeps the same dimensions as the conventional leveling system for 1 Hz seismometers so that the broadband seismic sensor can be installed conveniently. Tolerance for leveling is less than 1°. A tilt of up to 20° is allowed for the leveling operation. A microprocessor controls the leveling procedure. Some of the newly developed ocean-bottom seismometers were deployed in the western Nankai trough, where slow earthquakes frequently occur. The data from the ocean-bottom seismometers on the seafloor were evaluated, and we confirmed that the long-term CBBOBS is suitable for observation of slow earthquakes. The developed ocean-bottom seismometer is also available for submarine volcanic observation and broadband seafloor observation to estimate deep seismic structures.

Opportunistic sightings of blue whales off Sydney, Australia

2021 ◽  
Author(s):  
Vanessa Pirotta ◽  
Robert Harcourt
Keyword(s):  
Marine Mammals ◽  
New South ◽  
Short Note ◽  
Balaenoptera Musculus ◽  
Blue Whale ◽  
South Wales ◽  
Tasman Sea ◽  
Migratory Movements ◽  
The Antarctic ◽  
Blue Whales

ABSTRACT Two subspecies of blue whale occur in Australian waters, (1) the pygmy blue whale (Balaenoptera musculus brevicauda) and (2) the Antarctic blue whale (Balaenoptera musculus intermedia). Understanding blue whale presence in Australian waters is critical to ensuring Australia’s protection of these marine mammals as both subspecies were heavily exploited during historical whaling. This short note documents pygmy blue whale sightings in New South Wales waters over the last 18 years. Observations were opportunistically made via citizen science and verified by scientists. Sightings in this note contribute to our limited knowledge of pygmy blue whale distribution along the east coast of Australia and may help understand the migratory movements of New Zealand pygmy blue whales off Australia and in the Tasman Sea. Overall, information presented in this note contributes to Australia’s national and international conservation efforts to protecting blue whales as a migratory and threatened species.

Unusual signals recorded by ocean bottom seismometers in the flooded caldera of Deception Island volcano: volcanic gases or biological activity?

2013 ◽  
Vol 26 (3) ◽  
pp. 267-275 ◽  
Author(s):  
Daniel C. Bowman ◽  
William S.D. Wilcock
Keyword(s):  
Video Camera ◽  
Hydrothermal Activity ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Deception Island ◽  
Long Period ◽  
First Case ◽  
Diurnal Distribution ◽  
Ocean Bottom Seismometers ◽  
Show Evidence

AbstractAn ocean bottom seismometer (OBS) network was deployed for 1 month at Deception Island volcano, Antarctica, in early 2005. Although only two volcano-tectonic and three long-period events were observed, the three OBSs located > 2 km apart inside the caldera detected over 3900 events that could not be attributed to known volcanic or hydrothermal sources. These events are found on one instrument at a time and occur in three types. Type 1 events resemble impulsive signals from biological organisms while type 2 and type 3 events resemble long-period seismicity. The largest number of events was observed in a region of volcanic resurgence and hydrothermal venting. All three types occur together suggesting a common cause and they show evidence for a diurnal distribution. The events are most likely to be due to aquatic animals striking the sensors, but a geological source is also possible. In the first case, these signals indicate the presence of a biological community confined to the caldera. In the second case, they imply widespread hydrothermal activity in Port Foster. Future OBS experiments should bury the seismometers, include a hydrophone, deploy instruments side-by-side, or include a video camera to distinguish between biological and geological events.

Exploration in the Shetland‐Faeroe Basin using densely spaced arrays of ocean‐bottom seismometers

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 490-501 ◽  
Author(s):  
Stephen Hughes ◽  
Penny J. Barton ◽  
David Harrison
Keyword(s):  
Velocity Structure ◽  
Physical Property ◽  
Seismic Exploration ◽  
Gravity Modeling ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Near Surface ◽  
Oil Reserves ◽  
Ocean Bottom Seismometers ◽  
Basaltic Layer

Recent exploration activity in the peripheral regions of the Shetland‐Faeroe Basin, offshore northwest Scotland, has led to the discovery of some of the largest oil reserves on the United Kingdom (UK) continental shelf. We present results from two ocean‐bottom seismometer profiles acquired by Mobil North Sea Ltd. across the center of the Shetland‐Faeroe Basin. These data provide a powerful tool for delineating long‐wavelength velocity variations and thus have potential for reducing the nonuniqueness associated with conventional seismic exploration methods. Analysis of the first‐arrival traveltime data using both forward and inverse ray‐based techniques produces a well constrained velocity‐depth model of the basin fill. We estimate that the uncertainty in the velocity structure is ±5% from a series of trial and error perturbations applied to the final models. The velocity structure of the Faeroe Basin has three principal layers: (1) a near‐surface layer with velocities in the range 1.6 to 2.2 km/s, (2) a 3.0–3.2 km/s layer which is characterized by a northwards structural pinch out in the center of the basin, and (3) a deeper laterally heterogeneous layer with velocities in the range 3.8 to 4.2 km/s. In the northwestern portion of the basin, a high velocity (5.0 km/s) basaltic layer is imaged dipping toward the southeast at a depth of 2–3 km. The basement is mapped at a depth of 7–9 km in the center of the basin. Gravity modeling provides independent corroboration of our models through the application of a velocity‐density relationship obtained from a synthesis of physical property measurements. Reflections from the Moho indicate a crustal thickness of 18 ± 3 km, suggesting that the basin is underlain by highly attenuated continental crust, but the velocities in the basement are closer to those of the Faeroe Islands basalts than the expected Lewisian gneiss, suggesting that it may be highly intruded.

scholarly journals Orienting and locating ocean-bottom seismometers from ship noise analysis

2019 ◽  
Author(s):  
A Trabattoni ◽  
G Barruol ◽  
R Dreo ◽  
A O Boudraa ◽  
F R Fontaine
Keyword(s):  
Noise Analysis ◽  
Automatic Identification ◽  
Identification System ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Landing Sites ◽  
Ocean Bottom Seismometers ◽  
Set Up ◽  
Sw Indian Ocean ◽  
Actual Orientation

Summary Breakthroughs in understanding the structure and dynamics of our planet will strongly depend upon instrumenting deep oceans. Progress has been made these last decades in ocean-bottom seismic observations, but ocean-bottom seismometer (OBS) temporary deployments are still challenging and face set-up limitations. Launched from oceanographic vessels, OBSs fall freely and may slightly drift laterally, dragged by currents. Therefore, their actual orientation and location on the landing sites are hard to assess precisely. Numerous techniques have been developed to retrieve this key information, but most of them are costly, time-consuming or inaccurate. In this work, we show how ship noise can be used as an acoustic source of opportunity to retrieve both the orientation and the location of OBSs on the ocean floor. To retrieve the OBS orientation, we developed a first method based on a combination of seismic and pressure data through the use of the acoustic intensity. This latter can be used to quantify the OBS orientation from the ship noise direction of arrival (DOA), which can then be compared with known ship trajectories obtained from the automatic identification system (AIS). To accurately relocate OBSs, we also developed a second method based on the hydrophone data which computes distances of acoustical sources by measuring time differences of arrival (TDOA) between direct and reverberated phases. The OBS location is then retrieved by fitting measured ship distances with known ship trajectories. In this study, a full network of OBSs deployed in the SW Indian Ocean was reoriented and a test station was relocated. We demonstrate that our new methods may quantify the OBS orientation with an accuracy of about one degree, and its location with an accuracy of a few tens of metres, depending on the number of ships used in the analysis.

Migration-Based Local Event-Location Workflow for Ocean-Bottom Seismometer (OBS) Records in Subduction Zones: A Practical Approach for Addressing a Large Number of Events

2021 ◽  
Author(s):  
Shinji Yoneshima ◽  
Kimihiro Mochizuki
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Real Data ◽  
Japan Trench ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
S Waves ◽  
Local Earthquakes ◽  
Ocean Bottom Seismometers ◽  
Event Location

ABSTRACT An efficient event-location workflow is highly desired to analyze large numbers of local earthquakes recorded by ocean-bottom seismometers (OBSs) in subduction zones. The present study proposes a migration-based event-location approach for evaluating OBS records to examine local subduction-zone earthquakes. This approach can significantly reduce the amount of manual time picks compared with conventional methods. The event-location workflow was designed to detect arrival onsets of both P and S phases. Synthetic tests have shown that the proposed migration-based event-location method is robust against different types of noise, such as environmental noise and local spike noise. This workflow was then applied to real OBS data in the off-Ibaraki region at the southern end of the Japan trench. The results show that this approach is applicable to real data from subduction-zone events: It gives reasonable agreement with manual time picks for both P and S waves and reasonable error bars, and it demonstrates a clear down-dip trend of seismicity. The results also show fair agreement with event distributions from previous studies of the off-Ibaraki region. This proposed workflow can be used to examine the seismicity of local earthquakes around the subduction zone using OBSs. This approach is especially effective when the seismicity is high and/or in cases in which long-term OBS monitoring has recorded a large number of events.

A microprocessor-based ocean-bottom seismometer

1993 ◽  
Vol 83 (1) ◽  
pp. 190-217 ◽  
Author(s):  
David F. Willoughby ◽  
John A. Orcutt ◽  
David Horwitt
Keyword(s):  
Free Fall ◽  
Acoustic Signals ◽  
Differential Pressure ◽  
Ocean Bottom ◽  
Ocean Bottom Seismometer ◽  
Serial Links ◽  
Natural Period ◽  
Scripps Institution ◽  
Ocean Bottom Seismometers ◽  
Spherical Pressure

Abstract For over 12 years, the Scripps Institution of Oceanography has operated a fleet of microprocessor-based ocean-bottom seismometers. These instruments free-fall to the seafloor and release their anchors and rise to the surface either at preset times or on receipt of an acoustic command. The instruments are contained in a single spherical pressure case and include geophones with a 1-Hz natural period, and differential pressure gauges responsive to acoustic signals between 0.003 and 30 Hz. Recent improvements described in detail here include the implementation of a C-44 bus 80C88 microprocessor and cassette recorders capable of storing up to 10 days of data digitized at 128 samples/sec, or 40 days at 32 samples/sec. In addition, tiltmeters have been installed in the instruments. Serial links to the processor and release timers provide for instrument checkout and the setting of time and data parameters from outside the pressure case. A portable laboratory also described here is used to prepare the instruments for deployment at sea.

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