Wide Aperture Array Research Articles

Source range and depth estimation of propeller cavitation bubble collapse transients in a multipath environment

An experiment is conducted in which a wide aperture array, which is proximate to the sea floor in water 20 m deep, records transits of two motorboats. Occasionally, acoustic transients, which are attributed to collapsing propeller cavitation bubbles, are observed to be superimposed on the continuous broadband radiated noise component of each of the array’s three widely spaced hydrophones. By measuring the time differences of arrival of the transient signals propagating via the direct path at adjacent pairs of hydrophones, passive ranging by wavefront curvature is used to estimate the range and bearing of the transient source. Next, the source depth is estimated by measuring the multipath delay of the surface reflected transient signal. Also, the spectrogram of a single hydrophone’s output is observed to display a Lloyd’s mirror interference pattern due to the direct propagation path of the broadband radiated noise combining with the indirect propagation path signal reflected from the sea floor. The reciprocal of the frequency difference between adjacent destructive interference fringe minima is equal to the multipath time delay. This multipath delay, which equates to the quefrency of the cepstrum’s first rahmonic, contains source range information. The results of the two passive ranging methods are presented.

High-precision acoustic localization of dolphin sonar click transmissions using a modified method of passive ranging by wavefront curvature.

When configured as a wide aperture array, only three hydrophones are required to localize dolphin sonar transmissions with unprecedented precision, even when the underwater sound scene of their natural habitat is complicated by many of them emitting echolocation "click" signals at the same time. Given the sensor position coordinates and speed of sound travel, the passive ranging by the wavefront curvature algorithm estimates the source range and bearing, using range difference measurements between signals, arriving at two adjacent pairs of widely spaced sensors. If the sensor positions are not strictly collinear, then the source range estimates are biased. This problem is overcome by modifying the input parameters to the basic passive ranging algorithm. The experimental results for the estimated source positions are found to agree with the predicted localization performance for a wide aperture array passive ranging sonar. The precision of the source bearing estimates is 0.005°, which is independent of the source range. The precision of the source range estimates degrades a hundredfold (from 2.5 cm to 2.6 m) for a tenfold increase in source range (33-318 m). A lower bound for the peak-to-peak source levels of Indo-Pacific bottlenose dolphins (Tursiops aduncus) is 183 ± 2 dB re 1 μPa for regular click pulses.

Accommodation, slip inversion, and fault segmentation in a province-scale shear zone from high-resolution, densely spaced wide-aperture seismic profiling, Centennial Valley, MT, USA

We acquired a ~9-km long, high-resolution reflection seismic profile in the Centennial Valley, Montana, to better understand the kinematics of basin bounding faults and their role in accommodating proposed right-lateral shear in the Northern Basin and Range adjacent to the Yellowstone hotspot. In pursuing these goals, our findings have also shed light on the development of hanging wall stratigraphy and seismic hazards for this part of the SW Montana seismic belt. Here we present the profile and a working interpretation that identifies fault inversion, and an oblique, anticlinal accommodation zone linking the Centennial and Lima Reservoir faults in the Centennial Valley. These interpretations are consistent with seismicity and GPS-geodetically observed right-lateral shear aligned with the Centennial Valley north of the Yellowstone hotspot. Data were acquired using dense, wide-aperture arrays and illuminate the subsurface stratigraphy and faults down to ~1200 m, showing that the basin is a half-graben with a southern depocenter driven by the listric geometry of the north-dipping Centennial fault. Reflectors onlap basement highs with growth geometry against these faults. Our interpretation of a bright basal reflection as the Timber Hill Basalt (~6 Ma) or related flow, is consistent with a late Miocene – Pliocene inception of the basin proposed by other research. We also note a small inversion structure that we interpret as local evidence of transpression in the shear zone. This transpression is part of the accommodation zone and seismogenic faults including the Lima Reservoir fault that has well-expressed Holocene surface ruptures a few kilometres west of the seismic line along the northern edge of the Centennial basin.

The shallow structure of Solfatara Volcano, Italy, revealed by dense, wide-aperture seismic profiling

Two active-source, high-resolution seismic profiles were acquired in the Solfatara tuff cone in May and November 2014, with dense, wide-aperture arrays. Common Receiver Surface processing was crucial in improving signal-to-noise ratio and reflector continuity. These surveys provide, for the first time, high-resolution seismic images of the Solfatara crater, depicting a ~400 m deep asymmetrical crater filled by volcanoclastic sediments and rocks and carved within an overall non-reflective pre-eruptive basement showing features consistent with the emplacement of shallow intrusive bodies. Seismic reflection data were interpreted using the trace complex attributes and clearly display several steep and segmented collapse faults, generally having normal kinematics and dipping toward the crater centre. Fault/fracture planes are imaged as sudden amplitude drops that generate narrow low-similarity and high-dip attributes. Uprising fluids degassed by a magmatic source are the most probable cause of the small-scale amplitude reduction. Seismic data also support the interpretation of the shallow structure of the Solfatara crater as a maar. Our results provides a solid framework to constrain the near-surface geological interpretation of such a complex area, which improves our understanding of the temporal changes of the structure in relation with other geophysical and geochemical measurements.

Velocity model estimation by full waveform inversion of time-lapse 4D passive seismic array data

SUMMARY In passive-source monitoring, an accurate velocity model is important to precisely estimate microseismic source locations, and to understand changes in reservoir properties. In this study, we employ frequency-domain full waveform inversion in order to obtain a high- resolution velocity model by exploiting full wavefields. We demonstrate the feasibility of the method for a surface geophone array by inverting for time-lapse 4D velocity changes in a realistic subsurface model. Our method successfully estimates the small velocity changes of a few percent within layers of 10s of meters, even for a single passive seismic source event. The analysis of wavepaths and gradients suggests that keys for the successful inversion are the use of full wavefields (both first and scattered arrivals), the vicinity of velocity changes to the source, and the wide-aperture surface array.

Sensing System Provides Synchronized Acoustic Measurements

Young Technology Showcase Silixa’s iDAS (intelligent Distributed Acoustic Sensor) offers a solution for permanent and continuous downhole production monitoring and reservoir monitoring by overcoming the cost and technology challenges encountered with traditional point sensors. The iDAS enables wide-aperture acoustic array observation even in harsh environments, like high-pressure, high-temperature wells, and negates the need for irreversible pre-completion sensor placement. The iDAS measures the full acoustic field along the unmodified optical fiber up to tens of kilometres in length with a spatial resolution down to 1 m, capturing the full amplitude and phase of the incident wave on the sensing optical fiber up to frequencies >100 kHz with a wide dynamic range (>120 dB). The system enables high-quality synchronized coherent digital recording of acoustic waves with no crosstalk at every location along the fiber. These unique attributes make the iDAS technology particularly well-suited to the demanding applications encountered in oil and gas exploration and production. Principle of Measurement The iDAS functions by using a method based on optical time-domain reflectometry. When light is emitted into a fiber, the signal is reflected throughout the fiber length. These reflections are the result of a variety of mechanisms, including Rayleigh, Brillouin, and Raman scattering. By monitoring this scatter as a function of time following the emission of each sensing pulse, it is possible to build a map of the time variance of light-scattering properties throughout the fiber. This information can be analyzed to give a measure of the acoustic signal at each sensing zone along the fiber. Silixa’s iDAS uses a new digital optoelectronics architecture to rapidly and accurately measure this backscattered signal with a precision and speed that allows acoustic measurements from very low frequencies (<10 mHz) to high frequencies (>100 kHz). This sensing system can be retrofitted on existing standard optical-fiber cable installations, although superior performance can be achieved by using Silixa’s proprietary cables for logging operations and new permanent installations. Applications Silixa’s iDAS technology provides benefits through every stage of the life of a well. Since iDAS makes it possible to map acoustic propagation along the entire length of a borehole, the system creates the opportunity to perform real-time, continuous production and well-integrity monitoring. Further, distributed acoustics can facilitate seismic profiling in harsh, high-temperature downhole environments. Silixa has also developed a number of installation techniques for permanent as well as logging applications.

Wide aperture array design with constrained outer probe dimension

The invention presents solutions for large apertures of an ultrasound array under given dimension constraints given by the application for the ultrasound probe, for example by an endoluminal application. The invention has applications to annular arrays for 2D and 3D imaging, and also to linear or curvilinear arrays for 2D and 3D imaging. The invention further provides large aperture of arrays for dual frequency band operation with large difference between the dual bands.

Fiber optic acoustic sensor technology

Fiber optic sensor technology has been under development for over 25 years, recently a major milestone has been reached- the introduction of the Fiber Optic Wide Aperture Array on the first Virginia class submarine. This paper will review the development of this technology, outlining the principles of operation and the technological developments that led to fiber optic interferometric sensors becoming viable for production in an advanced sonar system. The Fiber Optic Wide Aperture array is a large channel count planar array mounted on the side of the submarine, but fiber sensor technology is also being developed for both towed arrays (as a replacement for the Navy’s thin-line towed arrays) and for bottom mounted acoustic arrays for a number of Navy applications. This paper will describe the development of the fiber optic hydrophones for these applications as well as the optical interrogation techniques. One of the key features of fiber optic sensor technology is the ability to passively multiplex many hydrophone channels per fiber, several multiplexing techniques will also be described. Some of the issues and challenges of this technology, such as coherent noise for large channel count systems will also be briefly discussed.

Advanced sonar array concepts for small underwater vehicle applications

Low-frequency acoustic reception and high directivity are difficult to obtain simultaneously using small undersea (robot) platforms. The dimensions and geometry of the hydrodynamic shapes that are required for efficient transit through the water preclude the use of broad apertures required for low-frequency directional applications. This paper will present array concepts that could be considered the next step in developing low-frequency directional acoustic payloads for undersea research and exploration. The talk will include results of previous Navy experimental demonstrations of wide aperture arrays for small vehicles as well as future advanced sonar packaging concepts that rely on new transduction technologies. [Work supported by the U.S. Navy.]

In situ source level and source position estimates of biological transient signals produced by snapping shrimp in an underwater environment.

Biological transient signals produced by snapping shrimp are sensed underwater by a wide aperture array. The instantaneous range and bearing of the source position of each snap is estimated along with a source level equal to the peak-to-peak amplitude of the pressure impulse generated by the snap at a standard distance of 1 m from its point of origin. For a sample of 1000 snaps recorded in Sydney Harbour, the distribution of peak-to-peak sound pressure levels has a mean value of 187 dB (re 1 microPa) and an interquartile range of 185-189 dB (re 1 microPa). Plotting the Cartesian coordinates of the source positions of the biological transient signals over a period of time maps the two-dimensional spatial distribution of the local snapping shrimp population. The principal habitat is found to be geocoincident with a 120-m-long wharf, the closest point of which is 60 m from the middle of the receiving array. The passive ranging performance of the wide aperture array is evaluated by generating mechanical transient signals at selected positions along the wharf. Precise estimates of the relative times-of-arrival of the acoustic wavefronts lead to source range and bearing estimates with standard deviations of only 0.1 m and 0.005 degrees (respectively), in agreement with theoretical predictions.

Techniques for passive detection and localization of marine mammals using wide aperture arrays

SACLANTCEN is sponsoring a program entitled Sound Oceanography and Living Marine Resources Program, whose objective is to demonstrate dual use technology for passive detection and localization of marine mammals, which will assist in the implementation of acoustic risk mitigation policies when using high-power acoustic sources. A sea trial was conducted in August 1999 to evaluate marine mammal detection and localization techniques using a number of advanced passive arrays. Passive, bearing-only data from marine mammal vocalizations received on a towed horizontal line array and target motion analysis are used to localize whale position. The multipath arrival structure of received signals and a ray trace model are used to determine whale range and depth over time. Data from several stations, executed using three deployed vertical line arrays in the vicinity of diving whales, and triangulation of arrivals are used to track whale location in the horizontal plane, while beamforming of the vertical array data is used to track whale depth. Evaluation of these data and techniques will be used to formulate passive procedures for determining the presence of marine mammals prior to activation of high-power acoustic sources.

Fiber-optic sensors for acoustic array applications

Over the past 7 years there have been a number of impressive demonstrations of fiber-optic acoustic sensor systems with surveillance grade capabilities. These demonstrations range from single-element and small six-element arrays tests conducted in the Arctic (1990 and 1992), to a 128-channel capacity (64-populated channels), horizontal line array deployed off Point Loma in 1996. These fixed, surveillance arrays have wider bandwidths and larger dynamic ranges that their piezoceramic counterparts. As well as fixed arrays, hull-mounted array demonstrations (such as the lightweight wide aperture array) have met the stringent Navy performance specifications while eliminating all the outboard electronics to reduce the systems life-cycle costs. The lightweight planar array approach is a viable candidate for the NSSN WAA. To reduce system costs further, planar array approaches using fiber optics appear to be the candidate of choice for the next generation of submarine mounted arrays. The other area attracting attention is that of the all-optical towed array, where the reduction in wet-end cost is the prime driver. In this system concept, engineering functions required for the operation of the array are accomplished by a suite of fiber-optic sensors for temperature, pressure, heading, roll, pitch, and strain.

PiezogranTM: High sensitivity/low-cost composites for wide aperture arrays

A shift in US Navy emphasis from blue water to littoral regions has resultled in a need for improved acoustic devices. Wide aperture arrays will be hull-mounted, thereby making device weight critical. The Naval Research Laboratory has developed a unique, low-weight composite, transducer design, PiezogranTM, to address this need. Piezograns consist of discrete, polycrystalline piezoelectric-ceramic elements dispersed in an epoxy matrix between two pressure plates. These plates make a direct mechanical as well as electrical contact to the piezoelectric elements. This design approach uses a 1-3 composite structure for high-gain operation with the flexibility of variable element spacing and ceramic volume fraction while achieving both low tooling and fabrication costs. Independent tests of 3.8-cm diameter PiezogranTM prototypes have yielded high hydrostatic response (dh>150 pC/N) and capacitance of 1.18 nF. Ten-centimeter-square array panels have also been assembled and are currently undergoing testing. This presentation will focus on fabrication and assembly of the PiezogranTM transducers as well as material properties.

Angles-of-arrival and tropospheric multipath microwave propagation

A wide-aperture vertical array is described, the function of which is to determine experimentally the angle-of-arrival and amplitude of individual rays during tropospheric multipath propagation. The primary objective is to provide high-resolution estimates both in measured values and in time. Some experimental results are presented indicating that under such conditions, several rays are generated which are separated in angle-of-arrival by a significant amount, consistent with that predicted by ray-tracing. Significant variations in amplitude of the individual components in times in the order of a few seconds are also observed. Some evidence is presented linking the occurrence of deep fast fading to atmospheric buoyancy waves.

Comments on ‘Apparent velocity measurements for the lower mantle from a wide aperture array’ by L. J. Burdick and Christine Powell

Comments on ‘Apparent velocity measurements for the lower mantle from a wide aperture array’ by L. J. Burdick and Christine Powell

Reply [to “Comments on ‘Apparent velocity measurements for the lower mantle from a wide aperture array’”

Journal of Geophysical Research: Solid EarthVolume 86, Issue B12 p. 11931-11932 Commentaries Reply [to “Comments on ‘Apparent velocity measurements for the lower mantle from a wide aperture array’”] L. J. Burdick, L. J. BurdickSearch for more papers by this authorChristine Powell, Christine PowellSearch for more papers by this author L. J. Burdick, L. J. BurdickSearch for more papers by this authorChristine Powell, Christine PowellSearch for more papers by this author First published: 10 December 1981 https://doi.org/10.1029/JB086iB12p11931Citations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume86, IssueB1210 December 1981Pages 11931-11932 RelatedInformation

Apparent velocity measurements for the lower mantle from a wide aperture array

The California Institute of Technology (CIT) operates a dense network of short‐period vertical seismometers which we have used as a large seismic array to measure the azimuth of approach ζ and ray parameter dT/dΔ of teleseismic P waves. Analysis of over 145 globally distributed events indicates that the ζ and dT/dΔ values measured by the array are in close agreement with the values predicted by the U.S. Geological Survey event locations. Most ζ anomalies (measured minus predicted values) do not exceed 1°. The small magnitude of the anomalies suggests that the measured dT/dΔ values can be used to construct a radial velocity model for the lower mantle. The curve of dT/dΔ versus Δ is in agreement with the curve determined for the Tonto Forest Seismological Observatory (TFSO) by Johnson (1969). The two curves differ in that there is no compelling evidence in the CIT data for first‐ or second‐order discontinuities in the velocity gradient. It is shown that discontinuities in the dT/dΔ data proposed by Johnson near distances of 40.5, 49.5, 59.5, and 70.5° are due to a strong dependence upon azimuth to source. The same least squares straight line can be fit through the CIT and TFSO dT/dΔ values. Residuals from this straight line display the same azimuthal dependence at both arrays. A velocity‐depth curve has been constructed by Wiechert‐Herglotz inversion of the CIT dT/dΔ data. A current upper mantle model for western North America was used as the top of the velocity profile. It is also shown that if fine structure does exist in the lower mantle velocity profile, the best way to find it may be through a combined amplitude dT/dΔ study.