Sound properties produced by Korean rockfish Sebastes schlegelii in relation to body and swim bladder size

A quick and reliable active flying height calibration is critical in today’s hard disc drive short product development and high volume production cycles. In addition to the servo signals, passive HDI acoustic and proximity monitoring techniques are tracking equilibrium of the head gimble assembly and air bearing modes. Passive acoustic HDI monitoring had been proven to be capable in active head protrusion detection applications [1] where derived passive and active Air Bearing flying profiles help to set active flying clearance. With enhanced sensitivity, passive acoustic techniques such as AE can detect embedded particles [2]. The drawback of this technique is that noisy HDD environment causes loss of detectability of the useful AE signal [3]. Special attention has to be paid for extracting desirable HDI information. On the other hand, recording head based proximity probes are immune to torsional HDI modes and operate on pitch mode induced modulation. Advanced HDD today uses a combination of recording head based proximity sensors that are designed to sense HDI modulation at close proximity to the disc. It has to be pointed out that interpretation of proximity probe contact signatures always has been challenging.

The sound properties produced by the white-edged rockfish (Sebastes taczanowskii Steindachner, 1880) were compared with the body size. We conducted a tank experiment to compare the sound properties with body length, which ranged from 12.4 to 19.8 cm. Sound production was composed of pulses with a duration of 0.010-0.022 s and a peak frequency of 400-1000 Hz. Peak frequency decreased with fish and swim bladder size and pulse duration. The relationship between sound properties and body size may be useful for estimating the body length of the target species by using passive acoustic monitoring.

Passive acoustic monitoring techniques are useful for studying vocally active marine species, particularly in remote and difficult to access areas. In this study, three months of acoustic recordings were collected off Egmont Atoll, Chagos Archipelago in the central Indian Ocean to detect, characterise, and investigate temporal variability of delphinid whistles. A subsample (3.6% of the total dataset) was used to manually annotate whistles and test automated whistle detectors. Higher frequency whistles (6-25 kHz, n = 126) were manually classified into six categories: upsweep (56%), convex (19%), downsweep (13%), concave (5%), sine (4%), and constant frequency (3%). An automated whistle detector was evaluated under five detection thresholds (measured in dB): 5.5, 6.0, 6.5, 7.0, and 7.5 above background noise. The 6.5 dB threshold demonstrated the best balance between precision (0.9) and recall (0.5). The whistles were detected on 78% of days, with a bimodal diel pattern, where whistles peaked after sunrise (0800-1000 h) and before sunset (1600-1800 h), with fewer detections in the middle of the day and at night. This study highlights the value of passive acoustic monitoring techniques to better understand the delphinid occurrence in remote and understudied areas.

Listening to the Deep: Live monitoring of ocean noise and cetacean acoustic signals

: The long-term goals are to develop and improve glider-based and autonomous-platform-based marine mammal monitoring for Navy environmental compliance, as well as for basic scientific studies of marine mammals. Autonomous glider-based passive acoustic monitoring of marine mammal presence is particularly needed within the southern California offshore region, a site of significant naval training. We aim to create operational glider-based marine mammal detection, classification, and localization systems to provide timely information on marine mammal presence to support Navy mitigation efforts in the southern California region. An important aspect to achieving these goals is quantitative evaluation of the monitoring capabilities of passive acoustic systems, and separation of calling behavior from the effects of the environment.

: The long-term goal is to develop glider-based and autonomous-platform-based marine mammal monitoring for Naval environmental compliance, as well as for basic scientific studies of marine mammals. Autonomous glider-based passive acoustic monitoring of marine mammal presence is particularly needed within the southern California offshore region, a site of significant naval training. We aim to create operational glider-based marine mammal detection, classification, and localization systems to provide timely information on marine mammal presence to support Naval mitigation efforts in the southern California region. Our objective is to develop and test glider and autonomous-platform-based capabilities for marine mammal call detection, classification, and localization (DCL). Because of their long-duration on station time and acoustically silent operation, gliders provide attractive platforms for acoustic monitoring over extended periods of time, with significant processing capabilities for detection, classification and localization of marine mammal calls. For gliders to be effective in this role, efficient algorithms for automated detection and classification of marine mammal calls are needed. In addition, we are testing various autonomous platforms (submerged versus surface) for marine mammal call detection capabilities, and comparing these platforms against fixed bottom-mounted acoustic sensors.

Space–time and hybrid algorithms for the passive acoustic localisation of sperm whales and vessels

Mapping cetacean sounds using a passive acoustic monitoring system towed by an autonomous Wave Glider in the Southwestern Atlantic Ocean

Ecoacoustics: acoustic sensing for biodiversity monitoring at scale

Acoustical oceanography involves the use of inverse acoustic techniques to investigate physical and biological phenomena in the sea. Processes at the sea surface, including bubble formation from wave breaking, precipitation rates, and gas transfer across the air–sea interface, are all being interrogated using active and passive acoustic techniques. Novel methods for monitoring fish stocks, based on the acoustic properties of the swim bladder, are also receiving attention. The acoustic calls of marine mammals are being investigated as natural sound sources to characterize the ocean environment. New geo-acoustic models to marine sediments have been developed and incorporated into ambient noise inversion techniques for determining seabed properties. Time-reversal experiments have been conducted over ranges of several kilometers, successfully stabilizing acoustic arrivals and allowing fluctuations in the ocean to be characterized. Brief accounts of these topics will be presented.

The recently developedwave gliderhas the potential to be an effective unmanned platform for acoustic applications. We present the results of a variety of experiments that quantify this potential. The radiated self‐noise of the autonomous platform is evaluated using an integrated passive acoustic recorder during a set of field trials off the coast of Hawaii. We present the radiated noise spectra from these trials to illustrate the dependence on hydrophone location and sea state. Using the same instrumentation, we demonstrate the ability of a modified wave glider to detect marine mammals using passive acoustic monitoring techniques. We also evaluate the performance of the wave glider operating as an active acoustic gateway, highlighting the potential of this platform to serve as a navigation reference and communications relay for scientific, industrial, and military subsea assets. To demonstrate the potential of the wave glider platform to support acoustic navigation, we assess the performance of time‐of‐flight range estimation and seafloor transponder localization. These tests were performed using commercial off‐the‐shelf acoustic positioning hardware integrated with the wave glider to illustrate that the low self‐noise of the wave glider makes it possible to achieve acoustic positioning performance similar to previously reported results. Finally, we show that the glider can operate as a station‐keeping surface communications gateway and provide recommendations for its use. © 2012 Wiley Periodicals, Inc.

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.

Silent porpoise: potential sleeping behaviour identified in wild harbour porpoises

Defining an acoustic repertoire is essential to understanding vocal signalling and communicative interactions within a species. Currently, quantitative and statistical definition is lacking for the vocalisations of many dasyurids, an important group of small to medium-sized marsupials from Australasia that includes the eastern quoll (Dasyurus viverrinus), a species of conservation concern. Beyond generating a better understanding of this species' social interactions, determining an acoustic repertoire will further improve detection rates and inference of vocalisations gathered by automated bioacoustic recorders. Hence, this study investigated eastern quoll vocalisations using objective signal processing techniques to quantitatively analyse spectrograms recorded from 15 different individuals. Recordings were collected in conjunction with observations of the behaviours associated with each vocalisation to develop an acoustic-based behavioural repertoire for the species. Analysis of recordings produced a putative classification of five vocalisation types: Bark, Growl, Hiss, Cp-cp, and Chuck. These were most frequently observed during agonistic encounters between conspecifics, most likely as a graded sequence from Hisses occurring in a warning context through to Growls and finally Barks being given prior to, or during, physical confrontations between individuals. Quantitative and statistical methods were used to objectively establish the accuracy of these five putative call types. A multinomial logistic regression indicated a 97.27% correlation with the perceptual classification, demonstrating support for the five different vocalisation types. This putative classification was further supported by hierarchical cluster analysis and silhouette information that determined the optimal number of clusters to be five. Minor disparity between the objective and perceptual classifications was potentially the result of gradation between vocalisations, or subtle differences present within vocalisations not discernible to the human ear. The implication of these different vocalisations and their given context is discussed in relation to the ecology of the species and the potential application of passive acoustic monitoring techniques.

The study of echolocation traits can assist in developing robust tools for the detection and monitoring of bats. The advent of non-invasive and passive acoustic monitoring techniques has increased the availability of echolocation data including in highly diverse regions, such as South Asia, where 145 of the 155 extant bat species are known to use laryngeal, nasal, or lingual echolocation. However, information remains disperse with no existing review of the state of echolocation knowledge in this region. Here we present a review that collates and catalogues echolocation data to facilitate access and reveal general patterns and knowledge gaps. We conducted a systematic review that returned 35 peer-reviewed publications containing echolocation data to which we added ~6,000 unpublished recordings from various collections (including the open-source ChiroVox database). We created a foundational database reporting on six standard echolocation functional traits to be used in identification. The dataset provides data for ~60% (n = 86) of the echolocating bat species in South Asia, with 299 distinct observations (unique combinations of recording techniques, equipment, and conditions for a given species). Mapping data locations we describe spatial biases and propose priority regions for future work in areas where species richness is high, but echolocation knowledge is limited or completely absent. These priority regions largely fell within the Western Ghats and Eastern Ghats of India, northeastern India, and Sri Lanka, with smaller clusters in peninsular, western, and eastern India. Our review offers a first assessment and a ready-to-use echolocation dataset for bats in South Asia. We hope this motivates an appraisal of functional trait data collection in diverse and data-poor regions and facilitates future research.