Sound is considered an important aspect of an ecosystem and acoustic methods have emerged as effective tools for ecosystems research.Xincun Lagoon,Hainan Island,is an important ecosystem characterized by dense seagras...Sound is considered an important aspect of an ecosystem and acoustic methods have emerged as effective tools for ecosystems research.Xincun Lagoon,Hainan Island,is an important ecosystem characterized by dense seagrass,which has been declining due to increased human activities,raising great concerns.Previous studies have identified various threats to seagrass,including heavy metal pollution,poor quality water,and so on.In this study,we investigate sources and levels of noise in seagrass beds and attempt to point out potential threats from noise pollution.A line array of six hydrophones was deployed over a period of seven days,from January 15 to January 21,2024.The recordings captured various sounds from marine life,human activities,and natural processes.Biological sounds,such as fish sounds and whale calls,were the most prevalent.Low-frequency noise from wind and tide were often recorded.Xincun Bay hosts more than 1500 fishing vessels;however,due to bad weather conditions that kept most vessels docked during the recording period,only one segment of boat noise was recorded;it lasted for 7 minutes,exhibiting strong energy over a broad frequency band.This event underscores the necessity of long-term monitoring of noise to identify and evaluate not only boat noise but other noise sources,especially ones that are intermittent but strong,that were not encountered during the limited period of observation on which this report is based.展开更多
Presented in this study is a novel method for estimating the depth of single underwater source in shallow water,utilizing vector sensors.The approach leverages the depth distribution of the broadband Stokes parameters...Presented in this study is a novel method for estimating the depth of single underwater source in shallow water,utilizing vector sensors.The approach leverages the depth distribution of the broadband Stokes parameters to estimate source depth accurately.Unlike traditional matched field processing(MFP)and matched mode processing(MMP),the proposed approach can estimate source depth directly from the data received by sensors without requiring complete environmental information.Firstly,the broadband Stokes parameters(BSP)are established using the normal mode theory.Then the nonstationary phase approximation is used to simplify the theoretical derivation,which is necessary when dealing with broadband integrals.Additionally,range terms of the BSP are eliminated by normalization.By analyzing the depth distribution of the normalized broadband Stokes parameters(NBSP),it is found that the NBSP exhibit extreme values at the source depth,which can be used for source depth estimation.So the proposed depth estimation method is based on searching the peaks of the NBSP.Simulations show that this method is effective in relatively simple shallow water environments.Finally,the effect of source range,frequency bandwidth,sound speed profile(SSP),water depth,and signal-to-noise ratio(SNR)are studied.The findings indicate that the proposed method can accurately estimate the source depth when the SNR is greater than-5 d B and does not need to consider model mismatch issues.Additionally,variations in environmental parameters have minimal impact on estimation accuracy.Compared to MFP,the proposed method requires a higher SNR,but demonstrates superior robustness against fluctuations in environmental parameters.展开更多
This study investigates the effects of ocean boundaries on modal shapes in very-low-frequency(VLF,1–10 Hz)sound propagation through the deep ocean.Utilizing a normal mode solution formulated in terms of parabolic cyl...This study investigates the effects of ocean boundaries on modal shapes in very-low-frequency(VLF,1–10 Hz)sound propagation through the deep ocean.Utilizing a normal mode solution formulated in terms of parabolic cylinder functions(PCF),we demonstrate that boundary interactions induce a phase change reduction below-πat frequencies of several hertz.This reduction,in turn,forces a key transition in the solution,shifting the order of the PCF from integer to non-integer values.Analysis of the characteristic shape of the PCF versus its order reveals that these boundary-influenced modes exhibit an energy shift toward deeper regions and a weakened axial convergence of the underwater sound field.展开更多
厄加勒斯反曲(Agulhas Retroflection,AR)区域是印度洋和大西洋进行水体交换和热量传输的重要通道,此处的热输送过程对印度洋和大西洋的热含量变化有显著的影响。本研究基于高分辨率地球模拟器海洋环流模式(OGCM for the Earth Simulato...厄加勒斯反曲(Agulhas Retroflection,AR)区域是印度洋和大西洋进行水体交换和热量传输的重要通道,此处的热输送过程对印度洋和大西洋的热含量变化有显著的影响。本研究基于高分辨率地球模拟器海洋环流模式(OGCM for the Earth Simulator,OFES)模拟的结果,刻画了1980—2017年AR区域(35.0°S—41.2°S)20.0°E断面上的纬向热输送特征,着重评估了热输送(Q_(H))各项分量的贡献,并探讨了流场变化对Q_(H)的影响。结果表明,气候态下年平均Q_(H)为−0.74 PW(负值表示向西),其中,平均流主导的热输送Q_(MEAN)和非线性过程主导的热输送(Q_(NLR))分别为−0.45 PW和−0.29 PW。流场变化主导的热输送(Q_(VEL))与Q_(H)时间序列相关性最高(r=0.59),方差贡献率高达43.24%。进一步的合成分析结果显示,Q_(VEL)的变化主要受到厄加勒斯流(Agulhas Current,AC)和厄加勒斯回流(Agulhas Return Current,ARC)的经向移动、伸缩和强度变化的调控。当西向的Q_(VEL)较小时,西向AC的减弱幅度大于东向ARC的减弱幅度,使Q_(VEL)整体呈现正异常;而当西向的Q_(VEL)增强时,AC和ARC都有所增强,AC向南拓展、流幅宽度增加,从而使西向Q_(VEL)的量值大于东向,Q_(VEL)整体呈现负异常。此外,本研究采用厄加勒斯反曲点来表征AC-ARC环流系统的位置,比较了反曲点的纬向移动和热输送强弱变化之间的对应关系,结果表明,二者在年代际尺度上存在一定的正相关关系。本研究系统展示了AC-ARC环流系统时空变异与跨洋盆热输送的对应关系,证实AC-ARC的环流位置和结构变化都对热输送过程有重要的调控作用,有助于进一步理解AR区域的环流特征及其潜在的气候效应。展开更多
基金supported financially by the Director General’s Scientific Research Fund of Guangzhou Marine Geological Survey(Grant Number:2023GMGSJZJJ00029).
文摘Sound is considered an important aspect of an ecosystem and acoustic methods have emerged as effective tools for ecosystems research.Xincun Lagoon,Hainan Island,is an important ecosystem characterized by dense seagrass,which has been declining due to increased human activities,raising great concerns.Previous studies have identified various threats to seagrass,including heavy metal pollution,poor quality water,and so on.In this study,we investigate sources and levels of noise in seagrass beds and attempt to point out potential threats from noise pollution.A line array of six hydrophones was deployed over a period of seven days,from January 15 to January 21,2024.The recordings captured various sounds from marine life,human activities,and natural processes.Biological sounds,such as fish sounds and whale calls,were the most prevalent.Low-frequency noise from wind and tide were often recorded.Xincun Bay hosts more than 1500 fishing vessels;however,due to bad weather conditions that kept most vessels docked during the recording period,only one segment of boat noise was recorded;it lasted for 7 minutes,exhibiting strong energy over a broad frequency band.This event underscores the necessity of long-term monitoring of noise to identify and evaluate not only boat noise but other noise sources,especially ones that are intermittent but strong,that were not encountered during the limited period of observation on which this report is based.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12274348 and 12004335)the National Key Research and Development Program of China(Grant No.2024YFC2813800)。
文摘Presented in this study is a novel method for estimating the depth of single underwater source in shallow water,utilizing vector sensors.The approach leverages the depth distribution of the broadband Stokes parameters to estimate source depth accurately.Unlike traditional matched field processing(MFP)and matched mode processing(MMP),the proposed approach can estimate source depth directly from the data received by sensors without requiring complete environmental information.Firstly,the broadband Stokes parameters(BSP)are established using the normal mode theory.Then the nonstationary phase approximation is used to simplify the theoretical derivation,which is necessary when dealing with broadband integrals.Additionally,range terms of the BSP are eliminated by normalization.By analyzing the depth distribution of the normalized broadband Stokes parameters(NBSP),it is found that the NBSP exhibit extreme values at the source depth,which can be used for source depth estimation.So the proposed depth estimation method is based on searching the peaks of the NBSP.Simulations show that this method is effective in relatively simple shallow water environments.Finally,the effect of source range,frequency bandwidth,sound speed profile(SSP),water depth,and signal-to-noise ratio(SNR)are studied.The findings indicate that the proposed method can accurately estimate the source depth when the SNR is greater than-5 d B and does not need to consider model mismatch issues.Additionally,variations in environmental parameters have minimal impact on estimation accuracy.Compared to MFP,the proposed method requires a higher SNR,but demonstrates superior robustness against fluctuations in environmental parameters.
基金Project supported by the National Natural Science Foundation of China(Grant No.12204128)。
文摘This study investigates the effects of ocean boundaries on modal shapes in very-low-frequency(VLF,1–10 Hz)sound propagation through the deep ocean.Utilizing a normal mode solution formulated in terms of parabolic cylinder functions(PCF),we demonstrate that boundary interactions induce a phase change reduction below-πat frequencies of several hertz.This reduction,in turn,forces a key transition in the solution,shifting the order of the PCF from integer to non-integer values.Analysis of the characteristic shape of the PCF versus its order reveals that these boundary-influenced modes exhibit an energy shift toward deeper regions and a weakened axial convergence of the underwater sound field.
