Passive Acoustic System Research Articles

Vocalisation rates of the North Atlantic right whale (Eubalaena glacialis)

Vocalisation rates were measured from North Atlantic right whales (Eubalaena glacialis) in spring 1999-2000 in the Great South Channel and off Cape Cod, USA, and in summer 1999-2000 in the Bay of Fundy, Canada. Vocalisations were classed as either ‘moans’, ‘low-frequency (LF) calls’ or ‘gunshots’. Towed hydrophone recordings (36.1 hours) were made in 21 encounters where loose aggregations of right whales were within about 1,000m. Recordings were also made using acoustic tags attached by suction cups to ten different whales (29.5 hours). Tags also recorded depth data. Moan rates (sounds per aggregation per hour) were correlated with size of whale aggregation. Individual whales produced moans at ~ 0-10 per hour (recorded from tags and the towed hydrophone). Small aggregations (2-10) gave higher moan rates (usually < ~ 60 per hr) and larger aggregations ( > 10) higher still ( ~ 70-700 per hr) (recorded from towed hydrophone). Results from the Bay of Fundy indicate high moan rates at night. Moans were usually produced in clusters. Tag data showed that moans were usually produced when whales were within about 10m of the surface. A passive acoustic system could potentially provide supplementary information on the distribution of aggregations of right whales. This could be useful for management (1) in the long term, by aiding the prediction of right whale distribution, or (2) as a real-time tool for helping to route shipping away from concentrations of right whales. The empirical evidence presented here on vocalisation rates will assist in assessing feasibility. The clustering of moans and the tendency to produce them near the surface could hamper detection and localisation efforts. Further research is underway to investigate other important practical issues such as detectability and source levels.

An Optical Imaging System for Capturing Images in Low-Light Aquatic Habitats Using Only Ambient Light

It is preferable that methods for monitoring fish behavior, diversity, and abundance be noninvasive to avoid potential bias. Optical imaging facilitates the noninvasive monitoring of underwater environments and is best conducted without the use of artificial lighting. Here, we describe a custom-designed optical imaging system that utilizes a consumer-grade camera to capture images in situ in ambient light. This diver-deployed system can be used to collect time series of occurrences of animals while concurrently obtaining behavioral observations for two weeks to a month (depending on the sampling rate). It has also been configured to be paired with a passive acoustic system to record time-synchronized image and acoustic data. The system was deployed in a protected kelp forest off southern California and captured >1,500 high-quality images per day over 14 days. The images revealed numerous fish species exhibiting biologically important behaviors as well as daily patterns of presence/absence. The optical imaging system is a cost-effective tool that can be easily fabricated and improves upon many of the limitations of previous systems, including deployment length and image quality in low-light and limited-visibility conditions. The system provides a relatively noninvasive way to monitor shallow marine habitats, including protected areas, and can augment traditional survey methods by providing nearly continuous observations and thus yield increased statistical power.

Research on Positioning Accuracy of Passive Acoustic Positioning System Based on Feature Matching in Air

Passive acoustic localization is an important interdisciplinary research branch which combines acoustics, communication and signal processing. Passive acoustic positioning system, as an important part of battlefield sensing and monitoring system, has been paid more and more attention. Due to the disturbance of battlefield and other environments and the existence of measurement errors, the positioning accuracy often cannot meet the requirements. Passive acoustic positioning system, as an important part of battlefield sensing and monitoring system, has been paid more and more attention. Due to the disturbance of battlefield and other environments and the existence of measurement errors, the positioning accuracy often cannot meet the requirements. In multi-sensor passive location, the measured data of each array element is not only related, but also compensatory and redundant, so some people use the optimal data fusion algorithm as post-processing algorithm to improve the positioning accuracy. In this paper, the positioning accuracy of ground passive acoustic positioning system is analyzed based on feature matching method, and some useful conclusions are drawn.

Arctic Marine Data Collection Using Oceanic Gliders: Providing Ecological Context to Cetacean Vocalizations

To achieve effective management and understanding of risks associated with increasing anthropogenic pressures in the ocean, it is essential to successfully and efficiently collect data with high spatio–temporal resolution and coverage. Autonomous Underwater Vehicles (AUVs) are an example of technological advances with potential to provide improved information on ocean processes. We demonstrate the capabilities of a low-power AUV buoyancy glider for performing long endurance biological and environmental data acquisition in Northern Norway. We deployed a passive acoustic sensor system onboard a SeagliderTM to investigate presence and distribution of cetaceans while concurrently using additional onboard sensors for recording environmental features (temperature, salinity, pressure, dissolved oxygen, and chlorophyll). The hydrophone recorded over 108.6 hours of acoustic data during the spring months of March and April across the continental shelf break and detected both baleen and odontocete species. We observed a change in cetacean detections throughout the survey period, with humpback whale calls dominating the soundscape in the first weeks of deployment, coinciding with the migration towards their breeding grounds. From mid-April, sperm whales and delphinids were the predominant species, which coincided with increasing chlorophyll fluorescence values associated with the spring phytoplankton blooms. Finally, we report daily variations in background noise associated with fishing activities and traffic in the nearby East Atlantic shipping route. Our results show that gliders provide excellent platforms for collecting information about ecosystems with minimal disturbance to animals, allowing systematic observations of our ocean biodiversity and ecosystem dynamics in response to natural variations and industrial activities.

Identification of soundscape components and their temporal patterns in Kongsfjorden, Svalbard Archipelago

Time series measurements of ocean ambient sound were carried out using an autonomous passive acoustic measurement system deployed in Kongsfjorden, Arctic Ocean, between July 2015 and April 2016. Geophysical soundscape components, particularly that of sea ice melting and wind noise, were identified. The biological sounds produced by walruses in the form of knocking and tapping sequences fall in the range 0.2–4 kHz, and the bearded seal trill loud vocalizations occur between 0.35 and 1.2 kHz. The anthropogenic sources are mainly connected to the passenger and patrol vessels, with sound levels dominant at frequencies below 0.7 kHz. During summer, the sound levels are high due to the combined effect of geophysical and anthropogenic sources, whereas they decrease during the winter and spring seasons since the sea-ice cover effectively shields the sea surface at this time, preventing wind-generated sound. This study illustrates the seasonal variability of the soundscape components, and discusses the relationship of sea ice concentration to ambient sound levels in the Arctic fjords using the passive acoustic monitoring approach.

Searching for the FishOASIS: Using passive acoustics and optical imaging to identify a chorusing species of fish

Marine protected areas have been established off the California coast to ensure the persistence and resiliency of the marine ecosystems found here. Kelp forest habitats, in particular, support a diverse assemblage of fishes, many of which produce sound. From May to September 2017, a low-frequency (325–545 Hz) chorus was recorded near the kelp forests off La Jolla, California. The chorus begins each day approximately a half-hour before sunset and lasts for about 3–4 hours. During these times, spectral levels around 400 Hz increased by approximately 30 dB over, although there is significant day-to-day variability in received level. To identify the chorusing fish species, a Fish Optical and passive Acoustic Sensor Identification System (FishOASIS) was developed, consisting of a four-channel SoundTrap ST4300 acoustic recorder and four Sony α7s II cameras. Frequency-domain beamforming was used on signals recorded by the four-element, 20-m aperture, tetrahedral-shaped array to estimate the location of the fish chorus, which appears to be fairly fixed over time. The chorus also was used as a source of opportunity to measure transmission loss in order to determine whether kelp forests can act as acoustic refuges by sufficiently attenuating chorusing sounds. [Research supported by California Sea Grant and NSERC Postgraduate Scholarship-Doctoral.]

A review of green systems within the indoor environment

This paper reviews the state of art of vegetation systems and their effect on the indoor environmental quality (IEQ), based on scientific studies from the past 30 years. Some studies have shown that biophilic workspaces and interaction with plants may change human attitudes, behaviours, improve productivity and the overall well-being. Evapotranspiration from plants helps lowering the temperature around the planting environment and this can be utilised for air cooling and humidity control. Also, indoor greenery can be used to reduce sound levels as a passive acoustic insulation system. Living wall systems in combination with biofiltration are emerging technologies to provide beneficial effects on improvement of indoor comfort. Several studies have indicated that green systems may improve indoor air quality and that they have different pathways for pollutant removal of volatile organic compounds. The plant root zone in potted plants may be an effective area for removing volatile organic compounds under controlled conditions. In conclusion, the full capacity of plants in real-life settings will need to be clarified to establish the true pollutant-removal mechanisms and the general effect on IEQ. The effects of green systems in combination with mechanical elements such as conventional heating, ventilation and air conditioning would need to be studied.

Cross-correlation method for acoustic detection of small unmanned aerial vehicles

The availability of Unmanned Aerial System (UAS) to consumers has increased in the recent years, with it came the potential for negligent or nefarious misuse of them. Stevens Institute of Technology has built a passive acoustic system for low flying aircraft detection, the application of the developed principles and algorithms for UAS acoustic detection and tracking is presented in this paper. The application of the developed principles and algorithms for UAS acoustic detection and tracking is presented in this paper. Several experiments were conducted aiming to establish the characteristics of the emitted noise of UAVs of various sizes while airborne and demonstrate the processing required to detect and find the direction toward the source. The vehicles tested included popular quadrotors: DJI Phantom 2 Vision + , 3DR Solo, DJI Inspire 1 as well as larger semi-professional vehicles: Freefly Alta 6, DJI S1000. The small array of 16 microphones was used for data collection in the tests near local NJ airport. Acoustic signatures of the tested UAS were collected for stationary and flying UAS. We applied the algorithm for detection and direction finding based on fusing time difference of arrival (TDOA) estimates computed by finding peaks in the output Generalized Cross-Correlation (GCC) function. The cross-correlation signal process provided UAS detection and bearing for distances up to 250m while the spectrograms did not reveal acoustic UAS signatures at that distance. This work is being supported by DHS’s S&T Directorate.

A passive acoustic based system to locate leak hole in underwater natural gas pipelines

Underwater natural gas pipelines can be punctured for a variety of reasons, but the most notable are corrosion and aging. This study proposes a novel passive acoustic based system, to detect acoustic signals, locate the leak holes, and determine the size of the leak holes remotely. The nature of acoustic signals, which are generated by leakages in underwater natural gas pipelines, is also examined. The success of this proposed localization method, which is based on the received signal strength technique, is analyzed by numerical studies and simulation works. Parameters, which are used in the numerical studies, are taken from a hypothetical pipeline whose specifications are similar to Maghreb-Europe Gas pipeline. The proposed method is examined for various measurement numbers, underwater ambient noises, the diameters of the leak holes and receiver numbers. It is shown that leakages can be located with low average position errors from several kilometers by depending on underwater ambient noise, detection method, receiver number, source strength and measurement number.

Detection localization and tracking of aircraft using Sparse distributed passive acoustic system

Stevens Institute of Technology has conducted extensive long-term testing of acoustic systems designed to track low-flying small aircraft in remote location and recorded over 2 years of data. The system consisted of 4 nodes placed in difficult remote terrain with separation ranging 1–4 km, each node comprising a pyramid-shaped volumetric cluster of 5 microphones an embedded computer, and a pan-tilt-zoom camera steered to detected targets in real time. and communication device. Each nodes' computer performed direction of arrival finding communicated to a central computer collected that data and processed it to generate tracks and classify targets. The duration and the scale of the deployment allowed to identify and solve many problems, including the effects of propagation delays between station and on cooperative localization and tracking, the seasonal changes in environmental noise, persistent and transient noise sources, and the diversity of targets of opportunity and their signatures. The propagation de...

Research on improving detection sensitivity to acoustic based on coherent-OTDR distributed fiber-sensing system

Coherent-OTDR technology is one of acoustic distributed fiber-sensing systems. Because of the advantages of anti-electric magnetic field interference, anti-corrosion and flexibility, it has been attracting more and more interest. Because the sound pressure is weak, the strain generated on the fiber is tiny and the sensitivity of the sensing system is low. Although many research has been made on expanding measuring distance and improving response frequency, the acoustic signals in the experiments are always replaced by PZT's mechanical stretching. In this work, a device for increasing sensitivity for acoustic in the passive acoustic detection system based on coherent optical time domain reflection (C-OTDR) is promoted. A way of improving sensitivity partly based on a thin-walled corrugated tube was promoted. The thin-walled corrugated tube was used as the element to transmit the energy of acoustic into the vibration of fiber. In section 2, a mathematical model of sensing based on corrugated tube was established. Theoretical result shows that the vibration of fiber is mainly caused by the tube movement along the axis direction. And it also shows the linear relationship between the vibration and the sound pressure. The sensitivity of the improved sensing devices is calculated and a computational formula for sensitivity calculating are also given. In section 3, the C-OTDR acoustic distributed fiber-sensing systems are set up. Fiberring and three types of thin-walled corrugated tubes are used for acoustic sensing. The minimum detection sound pressure level reaches 60.1 dB and the phase sensitivity reaches 2.975 rad/Pa. The experimental phase sensitivity of different sensing devices with different parameters change similarly to the theory results. The experimental results show that the way of improving sensitivity and the mechanical model for calculating sensitivity are effective. This research provides theoretical and experimental basis for further development of distributed optical fiber sensing.

Problems and Possibilities of Passive Thermoacoustical Tomography

The problems and possibilities of passive thermoacoustical tomography are discussed. Algorithms for reconstruction of internal temperature in the human body are proposed. These algorithms take into account heat transfer and blood circulation and the absorption factor, obtained previously. The results of reconstruction of deep temperature in the human hand in simulations with the medium with a heated object are reported. These results support the possibility of the correlation measurements of the thermal acoustic radiation. Such measurements allow the information on ultrasound absorption by the object under study to be obtained and open the way to the development of a passive acoustic tomography system using a priori information on the absorption factor.

Passive acoustic system for tracking low‐flying aircraft

The following study presents the acoustic aircraft detection system designed for automated detection, classification and tracking of low-flying aircraft using a network of passive acoustic sensors. The system consists of multiple autonomously powered sensor nodes, each equipped with a microphone cluster, cameras and electronics that perform pre-processing and transmit the results wirelessly to a central processing station. The station fuses the data from sensors for finding the direction of arrival (DOA) of aircraft sounds then uses triangulation techniques for the target localisation. The calculated tracks were used for steering the cameras to the acoustically tracked target to capture pictures. The extended test spanning more than two years has uncovered many challenges that are part of such deployment including the impact of the weather, natural and man-made interfering sources of noise, effects of terrain and the variety of types and modes of operation of the targets of interest. During the deployment period, the system detected a significant number of targets of interest. Several control tests with different aircraft providing ground truth GPS for comparison with the acoustic tracking was also conducted.

Stevens acoustic research in the Hudson River

Stevens Institute of Technology conducted numerous acoustic tests in the Hudson River. The main instrument was Stevens Passive Acoustic Detection System (SPADES) that consists of a simple array with 5 hydrophones and that was initially developed for diver detection. Later, we collected a large library of acoustic signatures of various vessels and developed numerous algorithms for detection, tracking and classification. We present a brief review investigating acoustic applications in the Hudson River, including: Acoustic tomography tests were conducted for measuring the river currents. The difference of time of flight to emitter and receiver placed near the opposite bank of the River was used for calculating the current. Numerous tests were conducted for estimating the Impulse Response and its variation that can be used for prediction of reliability and operating distances for underwater acoustic communication. Noise measurements from passing boats were used for estimating the acoustic attenuation in a wide frequency band. Several other possible future researches may include: Time Reversal Acoustic Focusing for diver deterrence. Active/Passive acoustic fence for diver detection. Bubble curtain for the suppression of underwater noise from a pile drive.

Concrete temperature monitoring using passive wireless surface acoustic wave sensor system

In this paper, a novel nondestructive method for detecting temperature variations of concrete using a passive wireless surface acoustic wave (SAW) sensor system is described. Performance of the SAW orthogonal frequency coded (OFC) temperature sensors was evaluated in air, liquid, and concrete. To verify the response of the SAW sensor, temperature was also measured using commercially available thermocouples and compared with the extracted temperature in all environmental conditions. Analysis of the measured data showed that the SAW temperature sensor system was successful in detecting temperature over a wide range in all tested conditions with a high degree of accuracy and short interrogation time. When the sensors were embedded within a 2-in. thick concrete cover, the maximum read distance was approximately 4m.

Evaluation of green walls as a passive acoustic insulation system for buildings

Greenery on buildings is being consolidated as an interesting way to improve the quality of life in urban environments. Among the benefits that are associated with greenery systems for buildings, such as energy savings, biodiversity support, and storm-water control, there is also noise attenuation. Despite the fact that green walls are one of the most promising building greenery systems, few studies of their sound insulation potential have been conducted. In addition, there are different types of green walls; therefore, available data for this purpose are not only sparse but also scattered. To gather knowledge about the contribution of vertical greenery systems to noise reduction, especially a modular-based green wall, two different standardised laboratory tests were conducted. The main results were a weighted sound reduction index (Rw) of 15dB and a weighted sound absorption coefficient (α) of 0.40. It could be concluded that green walls have significant potential as a sound insulation tool for buildings but that some design adjustments should be performed, such as improving the efficiency of sealing the joints between the modular pieces.

Study on Passive Acoustic Orienting System Based on Line Array of Microphone

The drawbacks of active object orienting system which is difficult to guarantee the concealment and security are obvious. Hence, the passive object orienting system becomes the research focus. Based on line array of microphone, the passive acoustic orienting system collects and records acoustic signals. The acoustic signals are processed by Conventional Beamforming (CBF) algorithm. The hardware of system is proved to be effective in the sound acquisition experiments. The results of acoustic orienting experiments are given, which shows that the error of acoustic orienting is less than 1%. The system which implements acoustic orienting and has a high accuracy is the base of the latter research in the laboratory.

An adaptive quarter-wave tube that uses the sliding-Goertzel algorithm for estimation of phase

This paper describes an adaptive quarter wave tube used to attenuate a tone from the exhaust noise of a large diesel engine. A sliding-Goertzel algorithm was used to calculate the phase angle of the transfer function between a microphone in the adaptive quarter wave tube and in the main exhaust duct. The control system adjusted the length of the adaptive quarter wave tube until the phase angle was −90° and caused the sound pressure level at the cylinder firing frequency in the exhaust duct to be minimized. The system was able to adapt to changes in engine speed, exhaust gas temperature, and load applied to the engine. The results demonstrate that the sliding-Goertzel algorithm can be used effectively to estimate the phase angle in an adaptive–passive acoustic control system.

Active–passive acoustic system for underwater port protection

Active and passive acoustic systems may be used for port protection against threats from divers, free swimmers, Unmanned Underwater Vehicles, etc. Currently, underwater port protection is provided by Diver Detection Sonars (DDS), and Sonardyne has developed the market-leading active system, Sentinel. Stevens’ scientific research in passive acoustics led to the development of algorithms for threat detection that were realized in the Stevens Passive Acoustic Detection System (SPADES). Sonardyne and Stevens have formed a partnership to investigate a combined active/passive system that will leverage the functionality of existing sensors to design, develop, and produce a system with superior capabilities and performance as opposed to a single system. The combined system provides detection not only for underwater targets, but also for surface vessels. Possible configurations include: (1) a scenario where acoustic pulses emitted by the Sonardyne sonar and reflected by the target can be received and processed by SPADES; (2) an “acoustic fence,” whereby the detection of targets occurs as they cross a line between the transmitter and receiver. This configuration takes advantage of the significant increase in target scattering strength in the forward direction versus that from the backscatter; and (3) a fusion between detections and/or tracks from the passive and active sensors to provide an increased probability of detection and reduced probability of false alarm.

Acoustic signatures of small boats measured in controlled lake conditions

Measurements were conducted under controlled conditions at Lake Hopatcong, NJ, to compare acoustic signatures of various small boats. The tested boats included: an outboard-driven Panga, a multiple-outboard driven go-fast boat, an electric drive vessel, a personal watercraft (PWC), and two small outboard-driven rigid hull inflatable boats (RIBs). Stevens Passive Acoustic Detection System (SPADES) was used for acoustic measurements and the specially developed “Portable Vessel Data System” (PVDS) was used to record vessel position, speed, shaft RPM, and vessel orientation. Vessel acoustic Source Level measurements were conducted by comparing the recorded vessel acoustic signals with a signal generated by a calibrated emitter from the same point. Dependencies of acoustic signatures on boat speed and loading were also investigated. For several vessels, the Source Level decreased when its speed increased. Analysis of tonal components in the vessels acoustic signatures with Detection of Envelope Modulation on Noise (DEMON) allowed to determine the number of engines per boat and even the gear ratio for transformation of shaft rotation to the propeller rotation. [This work was supported by DHS S&T.]