Acoustic Monitoring Techniques Research Articles

Investigation of duty cycles for measuring activity in passive acoustic bat monitoring

Echolocating bats are important bioindicators that can be monitored effectively using passive acoustic monitoring (PAM) techniques. In PAM, duty-cycle-based temporal subsampling is often used to collect data at ON/OFF intervals to circumvent the limitations of recorder battery and storage capacity to enable long-term monitoring. However, potential bias introduced by temporal subsampling has not been systematically investigated for bat monitoring. Here, we use continuous audio recordings from the Union Bay Natural Area in Seattle in Summer 2022 to simulate the effects of temporal subsampling using different duty cycle parameters. We detected bat calls automatically using a deep learning model [Aodha et al., 2022, BioRxiv] and calculated three metrics as proxy for bat activity: number of calls, Activity Index (AI), and Bout Time Percentage (BTP). We found that although the number of calls and AI are more readily computable using the detected calls, BTP is likely a more accurate measure that relies less on the performance of automated call detection methods. In addition, reduced sampling for only a portion of the night (e.g., 4 hrs) was generally inadequate for capturing bat activity. Our results suggest that considering species-specific acoustic characteristics is crucial for reducing sampling bias for PAM of bats.

Anthropogenic activity, hydrological regime, and light level jointly influence temporal patterns in biosonar activity of the Yangtze finless porpoise at the junction of the Yangtze River and Poyang Lake, China.

Under increasing anthropogenic pressure, species with a previously contiguous distribution across their ranges have been reduced to small fragmented populations. The critically endangered Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis), once commonly observed in the Yangtze River-Poyang Lake junction, is now rarely seen in the river-lake corridor. In this study, static passive acoustic monitoring techniques were used to detect the biosonar activities of the Yangtze finless porpoise in this unique corridor. Generalized linear models were used to examine the correlation between these activities and anthropogenic impacts from the COVID-19 pandemic lockdown and boat navigation, as well as environmental variables, including hydrological conditions and light levels. Over approximately three consecutive years of monitoring (2020-2022), porpoise biosonar was detected during 93% of logged days, indicating the key role of the corridor for finless porpoise conservation. In addition, porpoise clicks were recorded in 3.80% of minutes, while feeding correlated buzzes were detected in 1.23% of minutes, suggesting the potential existence of localized, small-scale migration. Furthermore, both anthropogenic and environmental variables were significantly correlated with the diel, lunar, monthly, seasonal, and annual variations in porpoise biosonar activities. During the pandemic lockdown period, porpoise sonar detection showed a significant increase. Furthermore, a significant negative correlation was identified between the detection of porpoise click trains and buzzes and boat traffic intensity. In addition to water level and flux, daylight and moonlight exhibited significant correlations with porpoise biosonar activities, with markedly higher detections at night and quarter moon periods. Ensuring the spatiotemporal reduction of anthropogenic activities, implementing vessel speed restrictions (e.g., during porpoise migration and feeding), and maintaining local natural hydrological regimes are critical factors for sustaining porpoise population viability.

Characterizing the acoustic response of Thalassia testudinum leaves using resonator measurements and finite element modeling.

Seagrasses play an important role in coastal ecosystems and serve as important marine carbon stores. Acoustic monitoring techniques exploit the sensitivity of underwater sound to bubbles, which are produced as a byproduct of photosynthesis and present within the seagrass tissue. To make accurate assessments of seagrass biomass and productivity, a model is needed to describe acoustic propagation through the seagrass meadow that includes the effects of gas contained within the seagrass leaves. For this purpose, a new seagrass leaf model is described for Thalassia testudinum that consists of a comparatively rigid epidermis that composes the outer shell of the leaf and comparatively compliant aerenchyma that surrounds the gas channels on the interior of the leaf. With the bulk modulus and density of the seagrass tissue determined by previous work, this study focused on characterizing the shear moduli of the epidermis and aerenchyma. These properties were determined through a combination of dynamic mechanical analysis and acoustic resonator measurements coupled with microscopic imagery and finite element modeling. The shear moduli varied as a function of length along the leaves with values of 100 and 1.8 MPa at the basal end and 900 and 3.7 MPa at the apical end for the epidermis and aerenchyma, respectively.

Seasonal and diel activities of the Yangtze finless porpoise in natural and highly disturbed habitats: Implications for conservation planning of freshwater cetaceans

Abstract Knowledge of fine‐scale seasonal and diel activity patterns of animals provides insights into habitat utilization dynamics and informs conservation action planning against potential human impacts. Such information is particularly important for riverine cetaceans, such as the Yangtze finless porpoise, which is threatened by habitat loss and disturbances by a variety of human activities. Passive acoustic monitoring (PAM) techniques were used to survey the seasonal and diel activities of the Yangtze finless porpoise in two natural habitat patches of the Anqing Yangtze Finless Porpoise Natural Reserve, and in one highly disturbed area adjacent to the reserve. In the two natural habitat patches, significantly higher detection rates of porpoises were observed during autumn and winter. The detection rates during autumn and winter were significantly higher at night than during daytime, whereas during spring and summer the diel difference in porpoise detection rates was not statistically significant. In the highly disturbed habitat, the porpoise detection rates were significantly lower than those in the two natural habitats. Although seasonal differences in porpoise detection rates were not statistically significant, diel detection rates were significantly different in autumn and winter. Information on seasonal patterns of porpoise activities suggested strengthening monitoring and law enforcement during autumn and winter, during the period in which diel activity patterns implied a potential conservation gap during nighttime. Extremely low levels of porpoise activities in port areas implied an ecological impact of coastal engineering on megafauna viability through the alteration of habitat functionality. To provide information on animal occurrences and activities and to minimize the bias of ‘false‐absence’ from visual surveys, the census survey design should consider both visual and PAM techniques. In seasons when occurrences of river cetaceans and habitat use are increasing, heightened conservation monitoring and law enforcement efforts are required, particularly during nighttime.

Ground-truthing daily and lunar patterns of coral reef fish call rates on a US Virgin Island reef

Coral reefs comprise some of the most biodiverse habitats on the planet. These ecosystems face a range of stressors, making quantifying community assemblages and potential changes vital to effective management. To understand short- and long-term changes in biodiversity and detect early warning signals of decline, new methods for quantifying biodiversity at scale are necessary. Acoustic monitoring techniques have proven useful in observing species activities and biodiversity on coral reefs through aggregate approaches (i.e. energy as a proxy). However, few studies have ground-truthed these acoustic analyses with human-based observations. In this study, we sought to expand these passive acoustic methods by investigating biological sounds and fish call rates on a healthy reef, providing a unique set of human-confirmed, labeled acoustic observations. We analyzed acoustic data from Tektite Reef, St. John, US Virgin Islands, over a 2 mo period. A subset of acoustic files was manually inspected to identify recurring biotic sounds and quantify reef activity throughout the day. We found a high variety of acoustic signals in this soundscape. General patterns of call rates across time conformed to expectations, with dusk and dawn showing important and significantly elevated peaks in soniferous fish activity. The data reflected high variability in call rates across days and lunar phases. Call rates did not correspond to sound pressure levels, suggesting that certain call types may drive crepuscular trends in sound levels while lower-level critical calls, likely key for estimating biodiversity and behavior, may be missed by gross sound level analyses.

Impact Noise and Vibration Sources Induced by Heavy Gym Activities: Do They in Turn Unnecessarily, Indirectly Affect Our Health?

‘Good health and wellbeing’ is one of the key United Nations sustainable development goals (SDGs). By ensuring healthy lives and promoting positive wellbeing, physical and mental activities have been encouraged for all at all ages. In recent decades, fitness culture and industry has significantly grown in many countries to enhance healthy lives and positive wellbeing. With the vigorous development of the fitness industry, a gym has become one of the common facilities within a neighborhood or on a campus in order to promote more and more people to participate in fitness activities. At the same time, the rapid increase in gym construction also provides more employment opportunities for professional fitness coaches. On the other hand, excessive noises and vibrations stemming from certain heavy gym activities can be observed. Accordingly, the NIHL (noise-induced hearing loss) in a gym should receive more attention. According to critical literature reviews, the high-intensity noise in gyms is mainly caused by the drops of heavy steel bars or dumbbells. Today, most gyms adopt cushioned flooring in specific areas, but the effectiveness of noise suppression still needs to be evaluated. The purpose of this study was to investigate the possibility of hearing loss caused by noise doses in a gym. Noises derived from heavy gym sources (i.e., lifting of heavy weights) were monitored and collected for analyses in order to estimate the risk of NIHL in a traditional gym, as well as to assess the measurements against the authoritative criteria to derive some technical guidelines for fitness and gym managers. The outcome of this study will improve insights into acoustic monitoring techniques and practical management within a gym environment.

Estimating Livestock Grazing Activity in Remote Areas Using Passive Acoustic Monitoring

Grazing has long been recognized as an effective means of modifying natural habitats and, by extension, as a wildlife and protected area management tool, in addition to the obvious economic value it has for pastoral communities. A holistic approach to grazing management requires the estimation of grazing timing, frequency, and season length, as well as the overall grazing intensity. However, traditional grazing monitoring methods require frequent field visits, which can be labor intensive and logistically demanding to implement, especially in remote areas. Questionnaire surveys of farmers are also widely used to collect information on grazing parameters, however there can be concerns regarding the reliability of the data collected. To improve the reliability of grazing data collected and decrease the required labor, we tested for the first time whether a novel combination of autonomous recording units and the semi-automated detection algorithms of livestock vocalizations could provide insight on grazing activity at the selected areas of the Greek Rhodope mountain range. Our results confirm the potential of passive acoustic monitoring (PAM) techniques as a cost-efficient method for acquiring high resolution spatiotemporal data on grazing patterns. Additionally, we evaluate the three algorithms that we developed for detecting cattle, sheep/goat, and livestock bell sounds, and make them available to the broader scientific community. We conclude with suggestions on ways that acoustic monitoring can further contribute to managing legal and illegal grazing, and offer a list of priorities for related future research.

Dynamic mode decomposition: A feature extraction technique based hidden Markov model for detection of Mysticetes' vocalisations

The detection and classification of Mysticetes' vocalisations have evoked the attention of researchers over the years because of their relevance to the marine ecosystem. These vocalisations are gathered employing different passive acoustic monitoring techniques. The vocalisation datasets are accumulated over a period; thus, they are large and cannot be easily analysed manually. Consequently, efficient machine learning (ML) tools such as the hidden Markov models (HMMs) are used extensively to automatically detect and classify these huge vocalisation datasets. As with most ML tools, the detection efficiency of the HMMs depend on the adopted feature extraction technique. Feature extraction techniques such as the Mel-scale frequency cepstral coefficient (MFCC), linear predictive coefficient (LPC), and empirical mode decomposition (EMD) have been adopted with the HMMs to detect different Mysticetes' vocalisations. This article introduces the method of dynamic mode decomposition (DMD) as a feature extraction technique that can be adopted with the HMMs for the detection of Mysticetes' vocalisations. The DMD has emerged as a robust tool for analysing the dynamics of non-stationary and non-linear signals. It is a completely data-driven tool that decomposes a signal over a certain period of time into relevant modes. Here, these spatial-temporal modes are reconstructed mathematically to form reliable feature vectors of the decomposed vocalisation signals. The performance of the proposed DMD-HMM detection technique is demonstrated using the acoustic datasets of two different Mysticetes' vocalisations: Humpback whale songs and Inshore Bryde's whale short pulse calls. In both species, the proposed DMD-HMM exhibits superior sensitivity and false discovery rate performances as compared to the MFCC-HMM, LPC-HMM, and EMD-HMM detection methods. Likewise, this proposed DMD-HMM detection method can be extended to other Mysticetes' that produce characteristics sounds.

Movement and Space Use of Grass Carp in the Sandusky River, Ohio: Implications for Lake Erie Eradication Efforts

AbstractThe Grass Carp Ctenopharyngodon idella is an invasive species to the Laurentian Great Lakes that was first detected in the 1980s. The western basin of Lake Erie is the putative invasion front for the Great Lakes, with spawning known to occur in two of the basin’s tributaries (Sandusky and Maumee rivers). Targeted removal is being used to reduce Grass Carp abundance, with an ultimate aim of eradication in part to prevent spread and establishment in the other Great Lakes; response efforts are being concentrated in the Sandusky River due to its heavy use by Grass Carp and because it is the tributary where spawning occurs consistently. The goal of this research was to identify areas in the Sandusky River where Grass Carp aggregate and identify variables that influence movement to improve efficiency of response efforts. Movement and space use of 27 Grass Carp were monitored using acoustic telemetry. Detection data were used to estimate movement and daily detection rates and also used in a spatial capture–recapture model to estimate activity centers of tagged fish. Grass Carp movement was highest when daily discharge and water temperature exceeded 31 m3/s and 18°C, respectively, and next highest when discharge exceeded 31 m3/s and temperature was between 4.5°C and 18.0°C. Daily detection rates at receivers and concentrations of activity centers suggested that aggregations occurred between river kilometers (RKMs) 34 and 36 and at RKM 45. During spawning conditions, Grass Carp also aggregated near RKM 48.6, which is proximal to suspected spawning locations. We recommend concentrating response efforts in these general locations and using passive capture gear when Grass Carp are the most mobile. Response efforts could be further refined by using a variety of acoustic telemetry monitoring techniques, including fine‐scale positioning, real‐time receivers, and mobile tracking to provide precise location and timing for removal actions.

Reducing non-productive time of mud pump with acoustic emission monitoring techniques on fluid end parts

This research conducted for overcoming the high non-productive time (NPT) damage of fluid end part mud pump in the drilling of PT. Pertamina PDSI Drilling Rig # 42.2/N1500-E Well SWI-001 at Pali, South Sumatra, Indonesia. The purpose of this study is to provide a solution for detecting early worn out of fluid end part with the innovation of the electric audio module (EAM), which is suitable for conditions in the field. This EAM works using the method of detecting acoustic emission signals from piezoelectric sensors that arise due to the movement of the drilling fluid and fluid end part in the mud pump module body. Then the emitted pulse is forwarded to the EAM, and the results give through two outputs, namely the spectrogram graphic and the acoustic emission sound that enlarged through headphones. The results of this EAM innovation can reduce the NPT in PDSI Rig # 42.3/N1500-E from 34.5 hours to 0 hours, and monitoring can be done remotely up to more than 50 meters no longer on the spot. The application of EAM in drilling rig implies a modification in the maintenance of a mud pump from breakdown to predictive maintenance. It supports the safety aspect considering monitoring which can perform remotely.

CT-based simulation of ultrasound propagation and cavitation in the human body for the assessment of acoustic therapy monitoring in high intensity focused ultrasound

In situ control of therapy parameters based on real time monitoring of ablation targets is a promising strategy to improve the safety and efficacy of extracorporeal high-intensity focused ultrasound (HIFU). In this work, we present an approach to evaluate the accuracy of acoustic monitoring techniques using computational fluid dynamics simulation. In the numerical setup, computed tomography images are used to model anatomical structures that can scatter and dissipate therapy waves in the body of the patient, including fat, bone, tissues, and organs. An in-house, compressible flow solver is used to simulate ultrasound generation from a transducer, nonlinear focusing of the wave toward therapy targets in the body, and backscattering toward the body surface. The simulation also captures excitation of cavitation bubbles in the focal region and their influence on the pressure fields in the body. Sensing and processing of the scattered signals provide for acoustic monitoring. For demonstration, we apply this approach to HIFU-based lithotripsy that uses burst waves with a focal pressure of O(1) MPa and frequency of O(100) kHz. Accuracies of acoustic monitoring are compared for various sensing and signal processing methods in quantifying the effects of anatomical structures and cavitation on ultrasound irradiation into targeted kidney stones. Finally, we discuss the use of these numerical experiments for control and optimization of therapy parameters. [Work supported by NIH P01-DK043881.]

Ecoacoustics: acoustic sensing for biodiversity monitoring at scale

Ecoacoustics: acoustic sensing for biodiversity monitoring at scale

Diagnostics of seal and rod degradation in hydraulic cylinders using acoustic emissions

External leakage from hydraulic cylinders is of a major concern for the offshore oil and gas industry. This occurs mainly as a result of physical damage to the piston rod or due to degradation of the piston rod seals. Numerous studies have been conducted to diagnose leakage from hydraulic cylinders due to seal failure using fluid, pressure, accelerometer or acoustic emission-based condition monitoring techniques. However, very few attempts have been made to diagnose multiple faults in hydraulic cylinders at the same time. Therefore, in this study, acoustic emission-based condition monitoring technique is used to detect and separate acoustic emission features due to different faults that are observed in hydraulic cylinders. An experimental study was performed on a test rig using water glycol as hydraulic fluid. Experiments were performed with different combinations of seals (unworn, semi worn and worn seals), and piston rods (unworn and worn). Acoustic emission features such as root mean square, peak, mean, kurtosis, skewness, mean frequency, median frequency and bandpower were used to identify seal and rod conditions. By using acoustic emission median frequency and mean frequency features it was possible to detect and separate leakage, and seal and rod degradation in the test rig over a large range of hydraulic working pressures. This study indicates that acoustic emission monitoring can be a strong basis for future research to identify and segregate other types of faults that are observed in hydraulic cylinders.

A REVIEW ON ACOUSTIC SIGNAL PROCESSING IN ROTATING MACHINES

Condition monitoring has an important role in the enhancement of reliability of operation, reduction in major damages and improving operational efficiency of equipment’s and systems. Various non-destructive methods like oil analysis, wear and debris analysis, vibration analysis, temperature analysis and acoustic analysis is used in many industrial applications, renewable and non-renewable power plants, in engineering fields like fluid mechanics, concrete and infra structures in civil engineering, and reaming industries. In recent decades, acoustic monitoring techniques are emerging widely in vehicle industries, windmill, nuclear reactor, and thermal power plants for monitoring the condition of electrical or mechanical equipment’s. It has extended its application in diagnosis of health and fault condition of electrical machines due its low operating cost and continuous assessment for improving the life span, reliability, safety, performance, productivity and to decrease planned shutdowns. Acoustic signal processing is used in acoustic monitoring to monitor the healthy and faulty conditions of machines. The acoustic monitoring involves acoustic signal or data collection, signal processing, decision making, and fault diagnosis. In this paper, an overview of the advancements and developments in acoustic signal processing techniques for acoustic monitoring of electric machines are summarized.

Fin whale 40‐Hz calling behavior studied with an acoustic tracking array

Fin whale 40‐Hz calling behavior studied with an acoustic tracking array

On-Line non-intrusive Monitoring of Particulate Solid Materials in Gas Flowlines Using Acoustic Sensor and ML Techniques

This paper describes initial steps towards developing a real-time quantitative particulate solids’ (sand) monitoring system forMultiphase flowlines based on acoustic monitoring and machine learning techniques. The concentration and the velocity of thesolids were varied during experimental trials. A conventional contact microphone mounted externally to a production flowline bend was used for recording the emitted acoustic signal. Features extracted from the signal were used as input to Time DelayNeural Network (TDNN) with solids concentration and velocity label to a training set. The TDNN achieved low values ofnormalised root mean square error (NRMSE) for all the models compared to the classical neural network.

Acoustic Emission Characteristics and Failure Prediction of the Granite with Orthogonal Cracks under Compressive Loading

Natural joints existing in rock significantly affect the stability of long‐term served subsurface engineering. In this paper, granite specimens with two orthogonal cracks were made for uniaxial compressive tests. The acoustic emission monitoring (AE) and digital image correlation techniques were employed to record the acoustic events and cracking of rock. The stress, ring‐down count, and cumulative ring‐down count of AE during the tests were obtained. The b‐value of AE was calculated based on the magnitude and number of AE events. The relationship between the b‐value and rock cracking for the specimens with orthogonal cracks was discussed. Further, the effects of orthogonal cracks distribution on the b‐value and rock cracking were investigated. Experimental results show that the specimens with orthogonal cracks would undergo multiple cycles of energy accumulation‐release‐reaccumulation‐rerelease under the uniaxial compression. For the specimens with orthogonal cracks, the b‐value of AE was volatile but generally decreased until complete failure. Every cracking event during the loading made the b‐value drop and then the reaccumulation of energy made the b‐value increase or stable. The specimen with orthogonal cracks was more prone to initial cracking than the intact rock. The orientation of cracks had effects on the b‐value evolution and crack patterns. The b‐value reaching about 1.5 can be used as the failure precursor of specimens with orthogonal cracks.

Feasibility study on real-scale, self-healing concrete slab by developing a smart capsules network and assessed by a plethora of advanced monitoring techniques

The study presents the design, manufacturing and testing of the first concrete structural element that carries a plane network of long, brittle macro-capsules into which chemical repair agent circulates to provide autonomous and repeatable healing of formed cracks under service loads. The vascular network design emerges as the most promising concept based on a decade of research, the milestones of which are briefly reported. In this experimental attempt, the network of simultaneously occurring and interacting cracks formed on a real-scale steel reinforced concrete slab loaded under four-point bending are tracked by an integrated sensing configuration that combines advanced acoustic monitoring techniques (Acoustic Emission, Elastic Wave Tomography, Ultrasound Pulse Velocity measurements) with Digital Image Correlation and visual crack inspection. Macro-capsules rupture is depicted by AE monitoring of high energy burst signals. It is shown that effective healing occurs locally, detected by sealing of open cracks and regain in mechanical properties. Indicatively, pulse velocity regain up to 100% is detected on healed zones, result also obtained by elastic wave tomography. Limited repair is measured on cracks with openings larger than 0.5 mm. This outcome could only be verified by correlating the experimental evidence of different monitoring methods, highlighting the need for design optimization and establishment of an advanced tempo-spatial structural health monitoring protocol.

Foraging activity of sperm whales (Physeter macrocephalus) off the east coast of New Zealand

The occurrence and distribution of sperm whales in New Zealand waters is mainly known from whaling records or opportunistic sightings by the public and a systematic estimation of the abundance and distribution has never been conducted. In this study, we investigated the foraging activity and occurrence of sperm whales off the Eastern coast of New Zealand using passive acoustic monitoring techniques. Three acoustic recorders were moored to the ocean floor at different locations on the east side of the North and South Island to collect passive acoustic data from June 2016 until August 2017. A total of 53,823 echolocation click trains were recorded and analyzed to understand the spatial and temporal variation of sperm whale foraging activity. No difference in the foraging activity was found between night-time and day-time periods at any of the locations. Click train detections increased toward the south, suggesting increased foraging activity near Kaikoura. At each station, sperm whale foraging activity varied by month.

Biosphere reserve zones are equal in terms of katydid ecoacoustics

ABSTRACTGlobally, biosphere reserves (BRs) conserve biodiversity across a gradient of human disturbance, yet there is very little empirical research investigating the effectiveness of BRs. The aim here is to compare katydid song diversity and abundance across the three zones of the Kogelberg BR using acoustic monitoring techniques. An index of Acoustic Activity was used to determine katydid abundances from recordings. Only eight katydid species were recorded over the entire summer season, with the species accumulation curve reaching an asymptote. Katydid diversity and abundances were very similar across the three zones. Habitat quality had a greater effect on abundance than on species richness. No single katydid species was identified as a bioindicator, rather the entire assemblages are responsive to habitat quality. The low diversity of katydids relative to other biomes and to other insects within the KBR appears to come from a long history of fire and extreme weather events, as is the case for other vegetation dependent insect taxa in the region. While we expect lower biodiversity away from the BR core zone, some groups, like these katydids, are maintained equally well in the three zones, and have not to date been adversely affected by human activity.