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When an aspect-dependent target is insonified by an acoustic source, distinct features are produced in the resulting bistatic scattered field. These features were exploited in a process for estimating target aspect angles that was demonstrated on a real-world data set using models produced using simulation data. Bistatic scattering data was collected during an experiment in November 2014 in Massachusetts Bay using a ship-based acoustic source producing 7-9kHz LFM chirps and a steel pipe target. The true target orientation was unknown, as the target was dropped from the ship with no rotation control. The Autonomous Underwater Vehicle (AUV) Unicorn, fitted with a 16-element nose array and data acquisition payload, was deployed in broadside data collection behaviors around the target, and the ship was moved to create two target aspects. Scattering data was collected for each target aspect angle. A Support Vector Machine (SVM) regression model was trained using simulated scattering bistatic field data from the OASES-SCATT simulation package. This model was used to estimate the target aspect angles using the real data collected by the AUV during the experiment. The aspect angle estimates were consistent with experimental observations of relative source positioning based on ship position.

The French NDC currently receives data from a number of IMS-type infrasound stations. Continuous automatic processing of the data is being performed in the [0.02–4] Hz frequency band in order to detect and characterize coherent infrasonic waves. Known and quasi permanent infrasonic sources are needed to evaluate and improve upper-wind models. Microbaroms are detected throughout the year on a global scale. Their monitoring reveals clear periodic trends in the detected bearings, providing further confirmation that long-range propagation strongly depends on the atmospheric conditions, primarily on the seasonal variability of the zonal winds. Infrasounds generated by active volcanoes also offer a unique opportunity for atmospheric studies. Recent observations in Vanuatu (New-Hebrides Islands) covering one full year show a maximal peak-to-peak azimuth deviation of ∼15. Infrasound observations are used as input of an inversion procedure to evaluate more precisely the vertical structure of the wind above the stratosphere in a range of altitude unaccessible to ground based or satellite measurements. With the increasing number of IMS stations being deployed, continuing systematic investigations into infrasonic signals from volcanoes will certainly help to advance the development of operational infrasound monitoring, and significant contributions to the understanding of atmospheric propagation could be expected.

Ocean Networks Canada (ONC) operates long time series, ocean observatories in the Pacific and Arctic. These include the large VENUS and NEPTUNE observatories, many small community based observatories and the Underwater Listening Station (ULS) for the Vancouver Fraser Port Authority. Passive acoustic monitoring systems are a component of all ONC observatories and passive acoustic data quality is therefore a concern. All the observing systems have multiple underwater electronics and sensor types, many of which can negatively impact the passive acoustic sensor data. Hydrophone sensitivity degradation due to time, water absorption, and biofouling need to be assessed to ensure accurate ambient noise measurements and accurate vessel underwater radiated noise level measurements. The performance and suitability of the hydrophones for specific areas also needs to be assessed so the acoustic analysts can be aware of the hydrophone induced data limitations. ONC has been examining the use of in situ calibration verifications, spectral probability density (SPD) plots, spectrograms, and wave data as tools to assess the passive acoustic data quality. The preliminary findings on the impact of all of the above acoustic error sources are presented.

Southwest Fisheries Science Center (SWFSC) has used combined visual and acoustic techniques to monitor marine mammal populations for the past 8 yrs. Currently, SWFSC passive acoustic surveys of cetaceans require specially trained personnel to monitor hydrophone signals in real-time. While effective, this method is time-consuming and costly. Automated detection of cetacean vocalizations would be a valuable tool during SWFSC surveys, allowing for detection when experienced technicians are unavailable. This technique is advantageous because it significantly reduces effort and removes sources of human error and bias in detection ability. PAMGUARD 1.0 CORE software was evaluated for use in automated detection of cetacean acoustic signals. Three different detector configurations of PAMGUARD were evaluated. This work shows that the majority of whistle and click events can be detected using PAMGUARD software. All of the PAMGUARD trials were capable of detecting whistles and clicks of cetacean species with varying success. These techniques were field-tested at sea during a recent SWFSC marine mammal survey. Automated detection of beaked whales and Dall’s porpoise during this survey will also be discussed. It is our goal to integrate automated detection methods into SWFSC’s acoustic marine mammal monitoring protocol and this work is an important step in doing so.

A remote sensor system (60) and method for passively sensing environmental conditions, such as temperature and humidity, uses a magnetic impulse from an AC interrogation coil (68) to stimulate a magnetoelastic sensor (62) to generate an acoustic signal (AE) at the resonant frequency of the magnetoelastic sensor (62). The acoustic signal (AE) is received by amplifier (74), detected and displayed (76). The systems and methods are particularly suited for detecting environmental conditions in commercial pharmaceutical packaging, such as blister packs.

An ongoing challenge for underwater sonar systems is to discriminate a man made target (shell) from surrounding clutter returns and to provide robust classification features for the estimation of the physical target characteristics (e.g., shell thickness and material properties). To this end, time-frequency analysis, and, in particular, Wigner–Ville analysis, has been shown to provide a robust processing tool for interpreting the evolutional time dependent aspect of the scattered acoustic wave field from elastic shells. The design of a robust space-time-frequency bistatic sonar system to enhance the target detection of shells with the use of a sensor array will be presented. Practical implications for bistatic mine countermeasure sonar systems, using a network of autonomous underwater vehicles, will be discussed.

Remote assessment of scattering objects in the ocean by analyzing the statistics of backscattered returns has been of interest for decades. This presentation describes how simulated and measured backscatter results may be combined to assess the natural variability of fish density in extended schools. The simulations were based on numerical solution of Foldy’s (1945) equations for harmonic illumination of spherical and spheroidal aggregations of randomly-placed omnidirectional point scatterers. The aggregations contained hundreds to thousands of scatterers, and varied in size from 12 ≤ ka ≤ 32, where k is the acoustic wave number and a is the aggregation’s volume-equivalent radius. Based on thousands of realizations, simulated backscattered returns were found to be Rayleigh distributed independently of the scatterers’ and aggregations’ characteristics. However, the distribution of volumetric scattering strengths from echo-sounder measurements from natural fish schools is broader. When taken together, the two results suggest that backscattering from natural aggregations of fish might be well described by a weighted superposition of Rayleigh distributions with the weighting function being a natural aggregation characteristic that can be remotely monitored. Results from simulations and measurements at 38 kHz and 120 kHz are shown and compared. [Work supported by ONR and UM Advanced Research Computing.]

Two broadband active acoustic systems, in concert with traditional narrowband systems and nets, were used to study distributions of fish in three regions within the Gulf of Maine. The long-range multi-beam broadband system detected fish out to 15 km range and the downward-looking short-range broadband system detected fish throughout the water column close behind the ship. The multi-year (2007–2011) study revealed distinct spatial patterns of fish and corresponding echo statistics in each region—diffusely distributed, sparsely distributed compact patches, and long (continuous) shoals. The broadband capabilities of the sonar systems (each spanning 1.5—6 + kHz) uniquely allow observations of resonance phenomena of the local swimbladder-bearing fish. The observed resonances were consistent with the fish species, sizes, and depths that were concurrently sampled in each area from a second research vessel. Spectral peak analysis also interestingly revealed the presence of distinct modes, which may be useful indicators of mixed-species and/or mixed-sized (e.g., juvenile and adult) assemblages of fish. [Work supported by Office of Naval Research.]

In reviewing the statistics we treat the data in two passbands. For the lower frequency passband (0.25 to 1.5 Hz) we apply beam-steering techniques to identify the azimuth, horizontal trace speed, dominant spectral peaks, and rms pressure. Magnetic tapes from October 1979 to date contained over 1000 signals. We present several detailed case studies and summary histograms of statistics showing the distributions of azimuth, horizontal trace speed, duration, time-of-arrival, and other parameters. We discuss possible sources for some of these signals. From analyses of sonograph records providing data for a passband covering 1–20 Hz, we categorized over 20 signal types and presently are applying a portable observatory in an effort to identify the origins of local sources. To identify the locations of regional sources (typically at distances >200 km from an observatory) we will work with our colleagues at DOE using bearings from several observatories.

Assessing and mitigating the effects of anthropogenic noise on marine mammals is limited by the typically employed technologies of archival underwater acoustic recorders and towed hydrophone arrays. Data from archival recorders are analyzed months after the activity of interest, so assessment occurs long after the events and mitigation of those activities is impossible. Towed hydrophone arrays suffer from nearby ship and seismic air gun noise, and they require substantial on-board human and computing resources. This work has developed an acoustic data acquisition, processing, and transmission system for use on a Wave Glider, to overcome these limitations by providing near real-time marine mammal acoustic data from a portable and persistent autonomous platform. Sea tests have demonstrated the proof-of-concept with the system recording four channels of acoustic data and transmitting portions of those data via satellite. The system integrates a detection-classification algorithm on-board, and a beam-forming algorithm in the shore-side user interface, to provide a user with aural and visual review tools for the detected sounds. Results from a two-week deployment in Cape Cod Bay will be presented and future development directions will be discussed.