海底沉积物物理参数的声学反演模式

声学反演方程是声学探测沉积物物理参数的基础方程。基于声学理论和统计理论的声速反演沉积物物理参数的两种模式,运用南海海底沉积物声学物理数据验证、比较了两种反演模式,以反演孔隙度、含水量为例,得出基于双参数经验方程反演模式的适用性较强,但精度有待于提高;基于声速理论的反演模式反演南海海底沉积物物理参数有待于进一步完善。     

Acoustic impedance of marine sediments

A heavy walled steel tube has been used as an impedance tube for measuring the acoustic impedance of marine sediments. The acoustic characteristics of the water filled tube were found to be satisfactory for the measurements. Values of acoustic velocity and attenuation in the sediments were determined from the acoustic impedance measurements and found to agree with previously published data.     

浅水多波束换能器声学性能检测方法研究

浅水多波束换能器主要声学指标能够直接或间接地反映系统性能指标,因此利用水池试验对系统换能器声学性能指标进行检测,不但能够初步掌握系统的性能,而且可以降低湖试或海试的风险。通过概括多波束测深系统核心性能与换能器声学指标的对应关系,按照水声计量检定规程和方法,论述了主要声学指标的计算方法,研究了自由场条件下声学指标的检测方法和注意事项,并结合国产多波束系统水池试验,验证了方法的可行性。     

一种新型水下声学浮标在目标探测中的应用

针对海上目标探测问题, 将矢量水听器和Argo浮标相结合, 可构建一种具有水中目标探测能力的新型水下声学浮标平台。该浮标平台可多次上浮和下潜, 具有在位时间长、隐蔽性能高、成本低等特点, 单台水下声学浮标即可实现海上目标探测, 利用多台水下声学浮标可快速形成大面积区域覆盖能力。为进一步验证水下声学浮标对海上目标探测性能, 2019年8月在南海海区开展了多台水下声学浮标海上试验, 数据处理结果表明: 南海夏季典型声速剖面下, 水下声学浮标对船长42m航速8.4kn的水面航船目标最远探测距离可达13.8km, 目标估计方位均方根误差最优可达5°, 在水面航船距离最近的1.9km处, 目标估计方位标准差可达2°。     

浅海沉积声学原位探测系统研制及深海功能拓展

海底沉积物的声速和声衰减系数等声学特性参数是影响水下声场空间结构、水声通讯、水声设备使用性能、海底目标探测的重要因素。介绍了最新研制的浅海海底沉积声学原位测量系统的工作原理、结构组成和性能特点,并对系统在黄海和南海海底沉积物声学特性调查中的应用情况进行了总结。最后,对系统在满足深海应用方面的功能拓展进行了讨论和展望。     

声学应答释放器电路部分可靠性分析

声学应答释放器是一种对可靠性要求很高的海洋环境监测设备,文中对国家海洋技术中心研制的声学应答释放器进行了可靠性分析。首先介绍了声学应答释放器的电路构成及功能;然后依据可靠性建模相关理论完成电路部分可靠性模型建立,依据可靠性模型,预计了设备的固有可靠度;最后有针对性地提出改进措施,用于指导声学应答释放器设计,为释放器技术研究提供计算模型与可借鉴的经验。     

Studying characteristics of a fine layered structure of the lower troposphere on the basis of acoustic pulse sounding

Results of acoustic sounding of the lower troposphere with the aid of detonation generators of acoustic pulses are given. This sounding method is based on a partial reflection of acoustic pulses with shock fronts from vertical wind-velocity and temperature gradients continuously varying with height in the troposphere and on the penetration of reflected signals into the region of acoustic shadow. Experiments on tropospheric sounding were carried out on the ground of the Barva Innovation Scientific and Technical Center (Talin, Armenia) in September 2015. In these experiments, an antihail acoustic system was first used as a generator of acoustic pulses. Experimental results have been compared with data obtained earlier in similar experiments carried out in the vicinity of Zvenigorod with the use of a special detonation generator of acoustic pulses. Due to the high resolution (in height) of the sounding method, which reaches 1 m in the stably stratified lower troposphere within a height range of 250–600 m, the vertical profiles of layered effective sound speed inhomogeneities with vertical scales from a few to a few tens of meters have been retrieved. The influence of these fluctuations on the form and amplitude of acoustic signals at a long distance from their pulsed source has been studied.     

Acoustic evidences of gas in the continental slope sediments of the Gulf of Cadiz (E Atlantic)

Detailed reviews of high-resolution acoustic studies in the continental slope of the Gulf of Cadiz has revealed the following gas-related features: acoustic turbidity and blanking, bright spots, ancient and modern pockmarks, high-amplitude diffractions, acoustic plumes and turbidity in the water column, and BSRs. The origin of the gas is believed to be biogenic and thermogenic. The BSR-like acoustic anomalies occur intermittently in some areas of the upper slope and tend to occur in the volcanoes/diapirs. The pressure–temperature conditions deduced for the location of those acoustic anomalies do not correspond to the conditions of stability of gas hydrates. It is suggested that these volcanoes/diapirs intrusions may locally induce anomalously higher pore pressure conditions on the immediately surrounding sediments, affecting the stability field of the gas hydrates.     

基于卫星的水下载体实时水声定位模型

为适应水下载体高精度实时导航定位的需求,提出了基于卫星导航定位的浮标水声定位系统定位模式,主要讨论了长基线固定浮标定位系统和超短基线单体智能浮标系统的工作原理和点位计算模型,分析了水声定位系统定位的准确度和误差源,对促进全球海域实现全天候高精度完全水下自主定位具有一定的指导意义。     

海底沉积物颗粒因素在不同频率下对声衰减的影响

综合了多个沉积物声学测量的实验方案,提出适合研究柱状海底沉积物声衰减的实验方案。对黏土质粉砂的物理性质和声学性质作了相关处理,得到了在高、低两种测量频率下该类型沉积物的波形特性、频谱特性和与沉积颗粒因素有关的孔隙度对声衰减比的影响。进一步作了相应的回归分析,低频时方差为0.169—0.175,高频时方差为0.029—0.032,尝试总结出黏土质粉砂类型沉积物在两种频率下的声衰减趋势。     

Localisation and phase transition of acoustic waves in a soft medium containing air bubbles

We study via numerical experiments the localisation property of an acoustic wave in a viscoelastic soft medium containing randomly-distributed air bubbles. The behaviours of the oscillation phases of bubbles are particularly investigated in various cases for distinguishing efficiently the acoustic localisation from the effects of acoustic absorption caused by the viscosity of medium. The numerical results reveal the phenomenon of `phase transition' characterized by an unusual collective oscillation of bubbles, which is an effective criterion to unambiguously identify the acoustic localisation in the presence of viscosity. Within the localisation region, the phenomenon of phase transition persists, and a remarkable decrease in the fluctuation of the oscillation phases of bubbles is observed. The localisation phenomenon will be impaired by the enhancement of the viscosity factors, and the extent to which the acoustic wave is localised may be determined by appropriately analyzing the values of the oscillation phases or the amount of reduction of the phase fluctuation. The results are particularly significant for the practical experiments in an attempt to observe the acoustic localisation in such a medium, which is in general subjected to the interference of the great ambiguity resulting from the effect of acoustic absorption.     

海水对海洋平台声发射传播特性影响研究

针对海洋平台水下钢结构无损检测的需要,研究在空气、淡水和海水作为耦合介质的情况下,声发射波在钢结构传播过程中幅值和能量的变化趋势,以及幅值和能量损失的原因。基于声发射波反射原理,分析声发射波在钢结构中传播的多径效应及波形转换特性,并解释了时域波形发生分离的原因。根据实验结果,分析了盐度对声发射波传播特性的影响。该项研究为提高海洋平台声发射检测中故障源的精确定位提供了实验依据。     

海底底质声学性质原位测量技术研究

系统介绍了海底底质声学性质原位测量技术,提出了新的原位测量方法,并根据这一测量方法,初步设计制作了相应的海底原位测量仪器。利用初步制作的测量仪器在实验室内对砂质沉积物进行了模拟测量试验,仪器测量得到的沉积物声速与直接透射法测量获得的声速基本一致。在宁波近海海域进行了海上实际测量试验,获得了该测量区域海底底质的声速,验证了此测量技术的可行性,为进一步研发先进的海底原位测量仪器奠定了基础。     

Acoustic penetration of a silty sand sediment in the 1-10-kHz band

An experiment was performed to measure sediment penetrating acoustic waves to test a model of acoustic propagation, which is based on Biot's theory. Independent geophysical measurements provided model input parameters. A parametric sound source was used to project a narrow beam pulse into a silty sand sediment at a shallow grazing angle. The sediment acoustic waves were measured by an array of buried sensors and processed to measure wave directions and speeds. Two acoustic waves were observed, corresponding to the fast and slow waves predicted by Biot's theory. Discrepancies between model predictions and measured acoustic waves were examined, deficiencies in the model identified, and strategies for improvement postulated. The permeability and bulk modulus of the solid frame were of particular interest     

Amplitude calibration of an acoustic backscattered signal from a bottom-moored ADCP based on long-term measurement series

A possible approach to, and preliminary results of, amplitude calibration of acoustic signals backscattered from an ADCP moored at the bottom of the near-shelf zone of the Black Sea is considered. The aim of this work is to obtain vertical profiles of acoustic scattering signal levels, showing the real characteristics of the volume content of suspended sediments in sea water in units of conventional acoustic turbidity for a given signal frequency. In this case, the assumption about the intervals of maximum acoustic transparency and vertical homogeneity of the marine environment in long-term series of ADCP measurements is used. According to this hypothesis, the intervals of the least values of acoustic backscattered signals are detected, an empirical transfer function of the ADCP reception path is constructed, and it is calibrated. Normalized sets of acoustic backscattered signals relative to a signal from a level of conventionally clear water are obtained. New features in the behavior of vertical profiles of an acoustic echo-signal are revealed due to the calibration. The results of this work will be used in subsequent analysis of the vertical and time variations in suspended sediment content in the near-shelf zone of the Black Sea.     

一种简易的潜标辅助寻标定位系统

介绍一种自主研发的、结合GPS定位和水声测距于一体的潜标自动搜寻定位系统。系统由安装于搜索船只上的全球定位系统GPS接收机、水声释放器甲板单元、综合信号接收处理单元(由计算机组成),以及集成于潜标系统水声释放器上的水声应答系统组成。利用GPS定位原理,将GPS测得的定位信息,与水声测距技术相结合,实现潜标系统的空间定位,为潜标系统的可靠回收提供技术保障。     

珠江口外伶仃洋海底含气沉积物声波反射及衰减特征

高分辨率地震剖面显示,在珠江口外伶仃洋海底有大面积含气沉积物。根据含气沉积物地震反射特征将其分为声学空白、声学幕、声学扰动、不规则强反射顶部和相位下拉等类型。对含气沉积物声波衰减初步分析表明约在3.3kHz附近有一衰减峰值,将实际资料与理论模型计算进行对比,认为此峰值频率对应于等效半径约6mm的气泡的特征振荡频率,此等效半径气泡的阻尼振荡是引起声波衰减的主要原因。     

An overview of SAX99: acoustic measurements

A high-frequency acoustic experiment was performed at a site 2 km from shore on the Florida Panhandle near Fort Walton Beach in water of 18-19 m depth. The goal of the experiment was, for high-frequency acoustic fields (mostly In the 10-300-kHz range), to quantify backscattering from the seafloor sediment, penetration into the sediment, and propagation within the sediment. In addition, spheres and other objects were used to gather data on acoustic detection of buried objects. The high-frequency acoustic interaction with the medium sand sediment was investigated at grazing angles both above and below the critical angle of about 30°. Detailed characterizations of the upper seafloor physical properties were made to aid in quantifying the acoustic interaction with the seafloor. Biological processes within the seabed and the water column were also investigated with the goal of understanding their impact on acoustic properties. This paper summarizes the topics that motivated the experiment, outlines the scope of the measurements done, and presents preliminary acoustics results     

The physical model with temperature and pressure controlled for measuring acoustic velocity of marine sediments

Abstract

The superficial marine sediment is an important boundary of ocean acoustic propagation. So, the acoustic property of seafloor surface is always research hotspot. The acoustic property of sediment is affected by temperature and pressure which is not considered by conventional lab acoustic measurement. A new type of system, called “Small-scale Geo-acoustic Physical Model Pilot System” (SGPMP) has been developed. The system measures geo-acoustic property of sediment under specific temperature, pressure and frequency conditions which can be controlled conveniently and accurately. The components, structure, measurement principle, error analysis and application example of this system are introduced in this article. As a laboratory platform, the system makes it convenient for us to study the relationship between the temperature, pressure, frequency and acoustic properties of marine sediment.