Search

The construction of marine ranches can enrich and conserve the fishery resources and improve themarine ecosystem, which helps realize the sustainable utilization of these resources. Sebastes schlegelii is a major breeding and releasing fish species in the marine ranches of North China. Its behavioral characteristics can be understood better by researching its vocalization, whichwill provide data support for constructing acoustic taming marine rancheswith S. schlegelii as the target fish species. However, there are few studies focusing on its sounds and behaviors. Therefore, based on the passive acousticmonitoring technology, the audios of underwater noises made by S. schlegelii were extracted using an AQH hydrophone. The high-definition internet protocol camera was used to monitor the behavior change of S. schlegelii. Then, by collating and replaying the collected audios and videos, the feeding behavior and biological noises of S. schlegeliiwerematchedtoanalyze their relationship. Results are as follows: (1) The noise of chewing settling granular baits (F5.0 mm) has a main frequency band and sound pressure level of 2000~4500 Hz and 96.53 ± 0.65 dB, respectively; in this feeding process, the main frequency band and sound pressure level of the swimming noise are 25~400 Hz and 95.63 ± 0.38 dB, respectively; the values are 500~700 Hz and 97.34 ± 4.91 dB, respectively, for the noise of flapping the waterwith the tail. (2) The sound signals emitted by S. schlegelii aremostly presented as single pulses during normal habitation or ingestion of baits on the surface of the water tank. However, S. schlegelii will attack and fight against each other when scrambling for baits, during which these signals are presented as continuous pulses. To sum up, the vocalization of S. schlegelii is closely related to feeding activities, and the sounds produced under different behaviors have specific biological significance. [ABSTRACT FROM AUTHOR]

The accuracy of (Global Navigation Satellite System) GNSS site coordinates is known have been impacted by human activities, especially for sites located in or near populated or urban areas. A better understanding of these human-originated noise sources would benefit GNSS research and applications. However, much less such studies have elucidated the error sources originated by human-induced environmental and mobility or migration effects, and their respective adverse impacts on GNSS positioning accuracy. Here we investigate the level of human originated noise reduction of GNSS site coordinate time series over mainland China during the ongoing coronavirus (COVID-19) pandemic from two main sources: the reductions of human-generated migration ground vibrations, and electromagnetic signal delays from the orbiting GNSS satellites to ground stations. We processed the GNSS height time series at selected 154 sites located in 110 cities in mainland China from 1 January 2017 to 25 March 2020, including the COVID-19 pandemic time period, to quantify the improved noise levels of GNSS displacement time series, and identified their correlations with the human migrations. We concluded the human-induced signal in continuous GNSS coordinate time series can be used as a real-time metric of regional human activity or migration intensity during COVID-19 episodes. [ABSTRACT FROM AUTHOR]

Increasing anthropogenic activities are threatening freshwater ecosystems worldwide. Sand mining in Poyang Lake has significantly impacted the wetland ecosystem over the past 20 years, yet a quantitative analysis of these impacts remains insufficient. Here, we used 63 Landsat images taken from 2000 to 2020 along with the support vector machine (SVM) method and a retrieval model of suspended sediment concentration (SSC) to identify sand mining vessels and areas affected by sand mining. Then, we analyzed the changes in landscape patterns in the areas affected by sand mining. The potential impact of underwater noise generated by sand mining vessels on Yangtze finless porpoises was analyzed by a sound propagation model. The number of sand mining vessels in Poyang Lake during the flood, normal, and dry seasons increased from 2000 to 2016 but rapidly decreased from 2017 to 2020. Sand mining vessels were mainly distributed in the northern channel from 2000 to 2006, moved toward the center of the lake from 2007 to 2010, then moved northward in 2017. Within the areas affected by sand mining, water and mudflats declined, grassland and sandbars increased, and the landscape discontinuity increased. The habitat of the Yangtze finless porpoise affected by underwater noise from sand mining vessels in all seasons has significantly increased overtime. The mean area of the affected habitats was 70.65% (dry), 64.48% (normal), and 63.30% (flood) of the total habitat areas. The porpoise habitats in the northern channel and the west branch of the Ganjiang River are more seriously affected by the underwater noise of sand mining vessels than the southern lake. The impact of sand mining activities on wetland landscape and aquatic species demands systematic investigation in the future. [ABSTRACT FROM AUTHOR]

The automatic modulation recognition (AMR) enables the receiver to automatically recognize the modulation type of the received signal for achieving correct demodulation. However, the noise and interference in the underwater acoustic channel greatly influence the features extracted from the signals. In this letter, we proposed the optimizing autoencoder (OAE) and the evaluation enhanced K-nearest neighbors (EEKNN) algorithms. The combination of OAE and EEKNN not only improves the feature discrimination but also avoids the misjudgment caused by abnormal samples and realizes accurate and efficient AMR. The experimental results of the data measured in the South China sea show that the proposed method successfully recognizes eight modulation types. The recognition accuracy is up to 99.25%, and the recognition time is only 3.48 ms. [ABSTRACT FROM AUTHOR]

Urban geophysics ups the ante in the world of applied geophysics, which requires innovative thinking and seemingly off-the-wall approaches, if for no other reason than the settings. Ambient-noise-tomography (ANT) can play a pivotal role in yielding subsurfa2ce information in urban areas, which is capable of dealing with challenges related to these scenarios (e.g., human activities and low signal-to-noise ratio). In this study, the ANT was conducted to investigate the near-surface shear-velocity structure in the surrounding area of the Baotu Spring Park in downtown Jinan, Shandong Province, China. Quiet clear Rayleigh waves have been obtained by the cross-correlation, which indicates that strong human activities, such as moving vehicles and municipal engineering constructions, can produce approximately isotropic distribution of noise sources for high-frequency signals. The direct surface-wave tomographic method with period-dependent ray-tracing was used to invert all surface-wave dispersion data in the period band 0.2-1.5 s simultaneously for 3D variations of shear-velocity (Vs) structure. Our results show a good correspondence to the geological features with thinner Quaternary sediments, the geological structural characteristic of the limestone surrounded by the igneous which has the highest velocity than that of the limestone in the study area, and several concealed faults of which specific location has been detected at depth. The results demonstrate that it is possible to successfully use ANT with high-frequency signal in an urban environment provided a detailed planning and execution is implemented. [ABSTRACT FROM AUTHOR]

Underwater sound generated by pile driving was recorded during the Hong Kong-Zhuhai-Macau Bridge (China) construction in 2014.The important parameters on the source level, the transmission loss, the time-frequency characteristics, and the method of the noise measurement were introduced in this paper. Signal analysis showed that the waveform of pile driving resembles a series of short pulses, composed of many different frequencies with main frequency energy distribution from 100 Hz to 2 kHz; the maximum value occurs at about 200 Hz. The best-fit shallow water sound propagation model gave a root-mean-square source level of 208.2 dB re $$1~\upmu \hbox {Pa}$$ at 1 m, a transmission spreading coefficient of 17.76, and an absorption coefficient of 0.015 dB/m. The value of transmission loss is in good agreement with the results calculated by the Marsh and Schulkin (M&S) semi-empirical expressions above 1 kHz, but is higher than the M&S results under 1 kHz, which may be due to the muddy seabed and turbid sea water in our study area. Although it is difficult to compare our research results with other studies as there is a lack of details on monitoring conditions (including pile size, hammer energy, environmental background, etc.), this paper provides a new method for underwater noise monitoring and analysis for pile driving in shallow water. [ABSTRACT FROM AUTHOR]

Underwater noise levels may be strongly influenced by sea ice. This study presents systematic measurements of under-ice ambient noise levels in shallow (<30 m) coastal waters using passive acoustic technology. Acoustic data were collected at 6 sites with different ice concentration (two levels: incomplete and complete ice cover) and thickness (three levels: <10 cm, 10–20 cm and >20 cm) in Liaodong Bay, China. Wind (max = 5.3 m/s) and current (max = 0.3 m/s) conditions were very weak, making minimal contributions to under-ice noise in this study. Root-mean-squared broadband (20–10,000 Hz) noise levels (BNLs) and one-third-octave-band noise levels (TOLs) at 63, 125 and 2000 Hz were measured. Median BNLs of the 6 recording sites ranged from 104.5 to 129.1 dB re 1 μPa, and median TOLs at 63, 125 and 2000 Hz were between 76.5 and 118.0 dB re 1 μPa at the 6 sites. Generalized Linear Models were used to analyze broadband and three one-third-octave-band noise levels in different ice concentration and thickness levels. The results showed that, regardless of the ice thickness, the sites with incomplete ice concentration had higher BNLs and 63, 125 and 2000 Hz TOLs than the sites with complete ice concentration, and regardless of the ice concentration, both BNLs and all three TOLs decreased with increased ice thickness. This study provides baseline characterization of under-ice noise in shallow coastal waters and indicating that both ice concentration and thickness have significant influence on the under-ice noise levels. These findings are important for future studies investigating acoustic communication and noise pollution in shallow coastal waters with sea ice. - First systematic measurement of under-ice noise levels for shallow coastal waters. - Ice concentration and thickness significantly influence under-ice noise levels. - Areas with incomplete ice cover or thinner ice thickness had higher noise levels. - The results are crucial for future noise pollution studies in sea ice environments. [ABSTRACT FROM AUTHOR]

The Yangtze River exhibits a high biodiversity and plays an important role in global biodiversity conservation. As the world's busiest inland river in regard to shipping, little attention has been paid to underwater noise pollution. In 2017, the underwater noise level in 25 riverside locations along the middle and lower reaches of the Yangtze River mainly at night time were investigated by using passive acoustic monitoring method. Approximately 88% and 40% of the sampled sites exhibit noise levels exceeding the underwater acoustic thresholds of causing responsiveness and temporary threshold shift, respectively, in cetacean. Noise pollution may impose a high impact on fish with physostomous swim bladders and Weberian ossicles, such as silver carp, bighead carp, goldfish and common carp, whereas it may affect fish with physoclistous swim bladders and without Weberian ossicles, such as lake sturgeon and paddlefish, to a lesser extent. Noise levels reductions of approximately 10 and 20 dB were observed in the middle and lower reaches, respectively, of the Yangtze River over the 2012 level. The green development mode of the ongoing construction of green shipping in the Yangtze River Economic Belt, including the development of green shipping lanes, ports, ships and transportation organizations, may account for the alleviated underwater noise pollution. Follow-up noise mitigation endeavors, such as the extension of ship speed restrictions and the study and implementation of the optimal navigation speed in ecologically important areas, are required to further reduce the noise level in the Yangtze River to protect local porpoises and fish. [Display omitted] • 88% sites in the Yangtze River can cause responsiveness in porpoises. • 40% sites in the Yangtze River can cause hearing threshold shifts in porpoises. • Noise impact are high on goldfish and common carp and low on sturgeon and paddlefish. • Follow-up noise mitigation endeavors are still required in the Yangtze River. [ABSTRACT FROM AUTHOR]

The hydro-acoustic noise radiating from underwater tunnels during vehicle passage may be harmful to aquatic fauna, and this is a particular concern for endangered species. Therefore, the effects of underwater noise radiation and propagation on aquatic biodiversity must be investigated. In this study, the dynamic response of the sediment and tunnel structure in the Yangtze River in China was explored by conducting a field test, and the associated noise radiation from the tunnel was recorded and investigated. A three-dimensional numerical model was then developed to simulate the vibration of the tunnel-sediment coupling system induced by random traffic-flow models. Next, a modal acoustic transfer vector-based method was used to predict underwater noise radiation by use of a three-dimensional finite-element acoustic model. Finally, the accuracy of the simulated results was verified by comparison with measurements. The results showed that the noise radiation induced by passing vehicles was approximately 14 dB greater than the background noise, with a main frequency range of 12–25 Hz. The random traffic-flow model had obvious influence of the simulated noise level above 20 Hz. Vehicle-induced underwater noise may thus have a direct effect on fish species that can perceive low-frequency sound pressure. The proposed method can be used for further investigation of methods to reduce the effect of underwater noise on aquatic fauna, especially endangered species. Image 1 • The vibration and noise radiation from an underwater tunnel induced by passing vehicles is measured and investigated. • A three-dimensional numerical method is used to predict the underwater noise with random traffic flow model. • The underwater noise with vehicle excitation is in low frequency range, about 14 dB larger than background noise. The main frequency range of underwater noise was found to be 12–25 Hz. The vehicle-induced underwater noise was approximately 14 dB greater than the background noise. [ABSTRACT FROM AUTHOR]

In past decades, the technologies of ship-building and engine-manufacturing have developed quickly, which may alter underwater radiated noise (URN) source levels. The URN from many merchant ships was recorded by self-sustained hydrophones mounted on the seabed near the ship lanes in the Yellow Sea of China. Twenty-seven samples of the recording are selected based on ISO and ANSI standards. The sources were assumed obeying Gaussian distribution in depth direction, and the ship source spectra were computed as a logarithmic average of source spectra calculated for different positions of ships to improve the fault tolerance of source position information. A key conclusion is that the estimated broadband ship noise source levels between 20 and 1000 Hz by RANDI-3 model are generally much greater than the measured results for ships whose length is larger than 200 m, though they are close for ships with length being less than 200 m. Furthermore, the data samples were divided into two categories to analyze. With each category, the 20–1000 Hz broadband noise of modern merchant ships is not highly correlated to ship length but closely related to ship speed. Finally, noise source spectrum models of the two ship categories were established, which express ship noise source spectra as a function of frequency, ship length and ship speed. The models can represent experimental results properly. • The ship samples were divided into two categories by length and their noise source spectrum models were established respectively. The fitting results are better than those estimated by RANDI-3 model. [ABSTRACT FROM AUTHOR]

Underwater sound plays an important role in some critical life functions of many aquatic animals. Underwater noise pollution has received relatively more attention in ocean systems. However, little attention has been paid to freshwater systems, such as the Yangtze River which is the habitat of critically endangered Yangtze finless porpoises (Neophocaena asiaeorientalis asiaeorientalis). In 2012, the underwater noise levels in 25 sites along the middle and lower sections of the Yangtze River were measured. The root mean square sound pressure level (SPL) and unweighted sound exposure level (SEL) at each site ranged between 105 ± 2.4 (median ± quartile deviation) and 150 ± 5.5 dB. Obvious spatial and temporal variations in the SPL were detected among the 25 sites. The SPL and SEL in the middle section of the Yangtze River were smaller (approximately 15 dB) and fluctuated more compared to those in the lower section. The power spectrum in the mainstem was site specific. However, all the spectra levels were higher than the audiogram of Yangtze finless porpoises. Majority of the sites had an averaged cumulative unweighted SEL (72%) and cumulative weighted SEL (68%) that surpassed the underwater acoustic thresholds for onset of hearing temporal threshold shifts for finless porpoise. Porpoise bio-sonars were detected in 89% of sonar monitoring sites indicating that noise pollution in the Yangtze River greatly threatened porpoise survival. In 8% of the sites, the averaged cumulative weighted SEL exceeded that of underwater acoustic thresholds causing non-recoverable permanent threshold shifts of finless porpoises auditory system whereas it was less than 1 dB below the underwater acoustic thresholds in other 8% of the sites. These sites urgently needed noise mitigation and management strategies. These results will facilitate the evaluation of the impacts of anthropogenic noise pollution on local finless porpoises and give further guidelines on its effective conservation. Image 1 • Spatial and temporal noise level variations were detected along the Yangtze River. • The noise levels in the lower section of the Yangtze River were relatively higher and more stable than those of the middle section. • Porpoise biosonars were detected in 89% of sonar monitoring sites. • Approximate 70% of the sites had noise levels surpassing the threshold to cause temporal threshold shifts to porpoise hearing. • Sites with an averaged cumulative sound exposure level exceeded and less than 1 dB lower than threshold causing injury to finless porpoise had an equal proportion of 8%. [ABSTRACT FROM AUTHOR]