原位测量技术在黄海沉积声学调查中的应用

介绍了最新研制的基于液压驱动贯入的自容式海底沉积声学原位测量系统及其在南黄海中部海底沉积声学调查中的应用。该系统可以实现对海底沉积物声速和声衰减系数进行原位测量,通过液压驱动装置将四根声学探杆匀速贯入到海底沉积物中,减少了对沉积物的扰动,可按照预设的工作参数在海底全自动工作,无需甲板上人员实时控制,采集的声波信号自容式存储于存储单元。系统工作水深为500 m,测量深度为1 m,测量频率为30 kHz,采样频率为10 MHz。使用该系统在南黄海中部获得了40个站位不同类型沉积物的声学特性原位测量数据,并使用CTD剖面仪对该系统声速测量进行了标定,相对误差均小于0.5%,表明该系统测量数据准确、可靠。     

便携式海底沉积声学原位测量系统研制及应用

详细介绍了最新研制的便携式海底沉积声学原位测量系统的工作原理和结构组成.与基于液压驱动的海底沉积声学原位测量系统相比,该系统操作简单,轻便灵活,易于吊放.2010年中国科学院南海海洋研究所“实验3”号科考船南海开放航次应用该系统在南海北部开展了海底沉积声学原位测量,首次获得该海区海底沉积物声速和声衰减系数原位测量数据.将原位测量声速与实验室测量声速进行了对比分析,结果表明二者存在明显差异,从而表明温度和压力等环境参数对沉积物声速具有重要影响.     

海底沉积物声学性质原位测量系统海上试验研究

提出了一种新的海底沉积物声学性质原位测量方法,介绍了新研制的海底沉积物声学性质原位测量系统。在青岛近海海域对该系统进行了海试,获得了各个站位的声速数据。将测得的各站位的声速与不同海域的沉积物声速进行对比分析,并对各个站位的声速与沉积物的平均粒径进行了相关性分析,发现与以往研究结果一致,沉积物声速与沉积物类型相关,不同类型的沉积物的声速有明显差异;声速与平均粒径相关性较好,粒径越大,声速越高。结果表明,利用海底沉积物声学性质原位测量系统测得的原位声速是正确的,它能快速准确地得到海底沉积物的声速值。     

海底沉积物声速-压力特性测试系统的设计与实验

文中设计基于可编程逻辑控制器(PLC)的测控平台、伺服加压控制、步进推动控制、多传感器测量、触摸屏交互等功能的温压可控声学测量系统,实现海底沉积物样品的孔隙水自动可控加压,通过声学测量功能单元测量海底沉积物在各个压力下的声速,模拟海底沉积物处于大陆坡2 000 m以浅海底表层任何深度变化时的声学特性测量,得到海底沉积物声速-压力特性,为校正实验室测量数据还原到海底原位测量数据提供一种方法。     

海底声学原位测试声速提取技术研究

海底沉积物的声学声速特性是沉积物声学中的一个重要的研究方向。正确提取声学原位测量的声速对海底沉积物声学反演至关重要。分析了海底声学原位测试系统的输出子波特性,提出了基于子波提取的互相关双向极值声速提取法。在声速提取过程中,发现某些通道实测声波到达时会出现超出正常范围的异常。分析后认为异常通道的到达波相位出现180°反至现象。通过互相关数值的负极小值提取的声波到达时对互相关正极大值所获得的到达时曲线进行校正后提取声速,得到了正确的结果,说明了本方法的正确性。     

关于海底沉积物声特性实验室直接测量方法的探讨

海底沉积物声学特性实验室测量是除原位(in situ)测量之外最直接的沉积物声学特性测量方法。作为一项基础性研究,利用声波参数仪准确测量海底沉积物的声速和声衰减对建立海洋地声学模型具有重要意义。文章针对RS- ST01C型数字超声测试仪在测量过程中所存在的一些问题进行了探讨,对规范海底沉积物声学特性实验室测量方法具有实际意义。     

海底底质声学原位测量电路控制系统研究

介绍了一种液压驱动贯入式海底沉积声学原位测量系统的电路控制单元的研究实现过程,以及该控制单元在南海北部海底沉积声学调查中的应用。该电路控制单元以Cortex-A8处理器为核心,集成大容量FLASH存储器,与单片机接口控制板进行串口通讯,实现对声学发射采集单元和机械液压贯入单元的可视化控制和监测。基于该电路控制单元,海底底质声学原位测量系统兼具自容式和在线式两种工作模式,可自容记录或实时采集声学原位测量单元在海底的工作状态数据、海底沉积物声速和声衰减系数等声学特性数据。该声学原位测量系统的实验室联调及南海海试结果表明,使用该电路控制单元对海底底质声学测量过程的监测与控制是有效的,对精确获取海底底质的原位声学特性有重要作用,可以促进海底底质声学原位测量系统的产品化。     

菲律宾海深海海底沉积物声学特性与物理性质相关关系

为研究深海海底沉积物声学特性与物理性质相关关系,于2016年11月在实验室对水深3164～5 592 m的菲律宾海深海海底沉积物柱状样品的声学特性进行测量,获取了沉积物声速、声速比、声阻抗、声阻抗指数等声学特性参数。结合沉积物的孔隙度和密度等物理性质参数,分析了海底沉积物声速、声速比、声阻抗、声阻抗指数与孔隙度、密度的相关关系,建立了该海域海底沉积物声学特性回归方程。研究结果表明:研究区深海数据与浅海回归方程符合度较差,与深海回归方程符合度较好;Hamilton校正方法有助于修正实验室测量引起的温度和压力误差,声速比与Hamilton方程符合度比声速好;声阻抗和声阻抗指数与物理性质参数的相关性优于声速和声速比。此外,研究认为由于海底沉积物的沉积环境较为复杂,其声学特性回归方程存在差异。由于上述差异的存在,在使用基于不同海域数据建立的回归方程进行海底沉积物声学特性预测时,应加以区别对待。该研究丰富了深海海底沉积物声学数据,对促进深海海底沉积物声学深入研究具有一定的借鉴意义。     

海底松散沉积物声学性质原位测量实验研究

分析研究了国内外海底松散泥沙的声速和声衰减系数测量的研究现状,并据此研制了海底表层沉积物声速声衰减系数原位测量系统。利用原位测量系统分别在实验室和海滩对不同粒度的沉积物进行了测量分析,得到了不同粒度沉积物的声速和声衰减系数。数据分析表明,沉积物的声速和声衰减系数与沉积物的粒径有密切的关系,粒径越粗,声速越高,声衰减系数越大。通过沉积物声学性质研究,可以开发海底浅层沉积物声学性质原位测量技术,提高相关海洋调查的速度和效率。     

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。     

海底沉积物的基本地声结构与地声模型

为准确建立海底地声模型,本文探讨地声模型的基本组成和基本结构。通过样品实验室测量,分析南海海底表层沉积物的密度、孔隙度与声速随着埋深变化的关系,得出海底实际存在的低声速表面–声速缓慢变化类型、低声速表面–声速增大类型、高声速表面–声速缓慢变化类型和高声速表面–声速增大类型4种典型地声结构;对比钻探测量,分析黄海海底沉积物的密度、孔隙度与声速随埋深变化关系,得出海底地声模型分层特征与地声结构组合特征。研究表明,地声模型可以归结为4种基本地声结构的组合,通过与底层海水声速、同层内声速剖面以及与上层海底沉积物下表面声速的比较,可以建立各种海底地声模型;基于实验室测量法建立的地声模型可以作为参考地声模型,但需要考虑实际海底温度和压力梯度以及海底沉积物的频散特性等,借助于声速比校正法和频散性理论模型进行计算及修正。     

Comparative Study of Sand Porosity and a Technique for Determining Porosity of Undisturbed Marine Sediment

Porosity is a fundamental property of marine sediment from which wet bulk density can be easily determined and used in a variety of geoacoustic, geotechnical, and sedimentological studies, analyses, and models. However, methods of sampling marine sands suffer from the common problem of core disturbance making the in situ porosity difficult to obtain. Embedding the sediment within an epoxy resin matrix will minimize the disturbance to the microfabric and preserve the in situ sedimentary structure for subsequent study. Image analysis can then be used on thin sections to study the microfabric and porometry. A comprehensive review and analysis of published data on the porosity of predominantly clean sands has been completed and a simple, accurate, and nondestructive technique is described for preparing and measuring the porosity of marine sediment (siliciclastic sand) that has been infiltrated aboard ship immediately upon sample collection and chemically fixed and infiltrated with epoxy shortly thereafter. The average porosity of 36 samples of marine sand collected offshore Fort Walton Beach, Florida, and embedded with resin was determined to be 41.30%. From the review of published data the average porosity of sand was determined to be 37.7%, 42.3%, and 46.3% for packed, natural (in situ), and loose packing conditions, respectively, for a range of sorting coefficients and grain sizes.     

Comparative Study of Sand Porosity and a Technique for Determining Porosity of Undisturbed Marine Sediment

Porosity is a fundamental property of marine sediment from which wet bulk density can be easily determined and used in a variety of geoacoustic, geotechnical, and sedimentological studies, analyses, and models. However, methods of sampling marine sands suffer from the common problem of core disturbance making the in situ porosity difficult to obtain. Embedding the sediment within an epoxy resin matrix will minimize the disturbance to the microfabric and preserve the in situ sedimentary structure for subsequent study. Image analysis can then be used on thin sections to study the microfabric and porometry. A comprehensive review and analysis of published data on the porosity of predominantly clean sands has been completed and a simple, accurate, and nondestructive technique is described for preparing and measuring the porosity of marine sediment (siliciclastic sand) that has been infiltrated aboard ship immediately upon sample collection and chemically fixed and infiltrated with epoxy shortly thereafter. The average porosity of 36 samples of marine sand collected offshore Fort Walton Beach, Florida, and embedded with resin was determined to be 41.30%. From the review of published data the average porosity of sand was determined to be 37.7%, 42.3%, and 46.3% for packed, natural (in situ), and loose packing conditions, respectively, for a range of sorting coefficients and grain sizes.     

Study on Sound-Speed Dispersion in A Sandy Sediment at Frequency Ranges of 0.5-3 kHz and 90-170 kHz

In order to study the properties of sound-speed dispersion in a sandy sediment, the sound speed was measured both at high frequency (90-170 kHz) and low frequency (0.5-3 kHz) in laboratory environments. At high frequency, a sampling measurement was conducted with boiled and uncooked sand samples collected from the bottom of a large water tank. The sound speed was directly obtained through transmission measurement using single source and single hydrophone. At low frequency, an in situ measurement was conducted in the water tank, where the sandy sediment had been homogeneously paved at the bottom for a long time. The sound speed was indirectly inverted according to the traveling time of signals received by three buried hydrophones in the sandy sediment and the geometry in experiment. The results show that the mean sound speed is approximate 1710-1713 m/s with a weak positive gradient in the sand sample after being boiled (as a method to eliminate bubbles as much as possible) at high frequency, which agrees well with the predictions of Biot theory, the effective density fluid model (EDFM) and Buckingham''s theory. However, the sound speed in the uncooked sandy sediment obviously decreases (about 80%) both at high frequency and low frequency due to plenty of bubbles in existence. And the sound-speed dispersion performs a weak negative gradient at high frequency. Finally, a water-unsaturated Biot model is presented for trying to explain the decrease of sound speed in the sandy sediment with plenty of bubbles.     

Study on Sound-Speed Dispersion in A Sandy Sediment at Frequency Ranges of 0.5–3 kHz and 90–170 kHz

In order to study the properties of sound-speed dispersion in a sandy sediment, the sound speed was measured both at high frequency(90–170 k Hz) and low frequency(0.5–3 k Hz) in laboratory environments. At high frequency, a sampling measurement was conducted with boiled and uncooked sand samples collected from the bottom of a large water tank. The sound speed was directly obtained through transmission measurement using single source and single hydrophone. At low frequency, an in situ measurement was conducted in the water tank, where the sandy sediment had been homogeneously paved at the bottom for a long time. The sound speed was indirectly inverted according to the traveling time of signals received by three buried hydrophones in the sandy sediment and the geometry in experiment. The results show that the mean sound speed is approximate 1710–1713 m/s with a weak positive gradient in the sand sample after being boiled(as a method to eliminate bubbles as much as possible) at high frequency, which agrees well with the predictions of Biot theory, the effective density fluid model(EDFM) and Buckingham's theory. However, the sound speed in the uncooked sandy sediment obviously decreases(about 80%)both at high frequency and low frequency due to plenty of bubbles in existence. And the sound-speed dispersion performs a weak negative gradient at high frequency. Finally, a water-unsaturated Biot model is presented for trying to explain the decrease of sound speed in the sandy sediment with plenty of bubbles.     

中国黄渤海沉积物声速与物理性质研究

In order to investigate the correlation between a sound velocity and sediment bulk properties and explore the influence of frequency dependence of the sound velocity on the prediction of the sediment properties by the sound velocity,a compressional wave velocity is measured at frequencies of 25–250 k Hz on marine sediment samples collected from the Bohai Sea and the Yellow Sea in laboratory,together with the geotechnical parameters of sediments.The results indicate that the sound velocity ranges from 1.232 to 1.721 km/s for the collected sediment samples with a significant dispersion within the series measuring frequency.Poorly sorted sediments are highly dispersive nearly with a positive linear relationship.The porosity shows a better negative logarithmic correlation with the sound velocity compared with other geotechnical parameters.Generally,the sound velocity increases with the increasing of the average particle size,sand content,wet and dry bulk densities,and decreasing of the clay content,and water content.An important point should be demonstrated that the higher correlation can be obtained when the measuring frequency is low within the frequency ranges from 25 to 250 k Hz since the inhomogeneity of sediment properties has a more remarkably influence on the laboratory sound velocity measurement at the high frequency.     

Variation of temperature-dependent sound velocity in unconsolidated marine sediments: Laboratory measurements

Laboratory measurements of sound velocity in unconsolidated marine sediment were performed to establish specific correction curves between temperature and sound velocity. Cores from the Hupo Basin and the southern sea of Geumo Island were cooled and sound velocity was measured while gradually increasing temperature (from 3 to 30°C). Sediment textural and physical properties (porosity, water content, and bulk density) were measured at the same depth. Sound velocity increases with temperature for clay, mud, silt, and sand sediment, resulting in values of approximately 2.65, 2.72, 2.78, and 3.10?m/s/°C, respectively. These results are similar to those of previous studies, and differences are likely due to density, porosity, and clay contents of the sediment. Using these results, we present correction curves for sound velocity temperature dependence for each sediment texture, which can be used to correct from laboratory to in situ values to develop accurate geoacoustic model.     

基于海底表层沉积物声速特征的南海地声模型

在由垂直声速梯度建立的地声模型基础上,通过引入沉积物与海水声速比和沉积物压缩波与切变波声速比两个表征沉积物声学特征参数得到更全面和有实际指导意义的地声模型。在沉积物声波传播FCMCM模型基础上,基于热作用和重力作用下沉积物两相介质的应力应变分析,建立TFCMCM和DFCFCM模型,运用模型校正表层沉积物声速特征来计算和解释地声模型。根据海底表层沉积物存在低声速和高声速两种类型,结合沉积物沿纵深孔隙度不变和变化两种类型,得到南海海底沉积物的两类四种典型地声模型:低声速孔隙度不变型、低声速孔隙度减小型、高声速不变型和高声速孔隙度减小型。运用这四种典型地声模型的组合解释了卢博提出的南海三种典型声速结构。认知声速结构将为南海声学探测海底、划分海底区域提供模型支持。