浅地层剖面系统在福建沿海海底沉船调查中的应用

海底沉船是水下文化遗产的一种重要类型和存在形式,利用综合地球物理手段对福建平潭、莆田及福州海域的海底沉船进行了探测研究,并重点探讨了不同浅地层剖面系统及不同探测频率在不同埋藏状态的水下文物调查中的应用。结果表明:浅地层剖面探测能够有效识别处于不同埋藏状态的沉船,尤其对探测埋藏海底面以下的沉船具有其他探测手段无法比拟的优势,但是探测频率的调节对目标物探测结果存在较大差异,对于埋藏式的海底沉船低频信号探测效果较理想。     

海底管道测量声学剖面特征分析

海底管道的位置与埋深测量通常采用浅地层剖面仪等声学手段来实现,由于海管与地层之间的声阻抗差异,会以绕射弧的形态出现在声学剖面中。但当海管埋设于管沟中时,管沟中断棱的绕射与海管绕射易于混淆,给声学剖面图的解译和识别带来困难。基于地震勘探原理,结合浅地层剖面仪的性能、挖沟作业对地层的扰动等,分析了管沟绕射弧的类型与特点、挖沟作业扰动的声学特征等,提出了管沟中海管绕射弧的识别方法。结果表明,正确认识不同类型管沟的绕射、施工扰动产生的绕射等声学特征,才能辨识出海管的绕射现象。实际工作中应根据测量海区的水深、土质、海管属性等多种要素,选用适宜的仪器类型及测量参数。     

Reflection Coefficient Calculation from Marine High Resolution Seismic Reflection (Chirp) Data and Application to an Archaeological Case Study

Chirp sub-bottom profilers produce high-resolution images of the near-surface. An attribute of the sea-bed reflection in chirp data are fluctuations in polarity between adjacent traces. Two models are proposed and presented to explain this: the first incorporates changes in an acoustic impedance gradient at the sea bed; the second uses changes in the thickness of the uppermost sediment layer. Mixing of adjacent traces produces a consistent polarity for the sea-bed reflector. Reflection coefficients are calculated, using amplitude information derived from single-traces, and polarity information from trace mixing, with application to a marine archaeological case study. The reflection coefficient calculated for the top of a buried 18th century wooden wreck is -0.26.     

Chirp sub-bottom profiler source signature design and field testing

Chirp sub-bottom profilers are marine sonar systems which use a highly repeatable source signature to facilitate the acquisition of correlated data with decimetre vertical resolution in the top 20–30 m of sediments. Source signatures can be readily developed and implemented, but an applicable methodology for assessing resolution and attenuation characteristics of these wide-band systems did not exist. Methodologies are developed and applied to seven contrasting source signatures which occupy the same frequency band, but differ in their Envelope and Instantaneous Frequency functions. For the Chirp source signatures tested, a Sine-Squared envelope function is shown to produce seismic data with the optimum resolution and penetration characteristics.     

Relations entre la réponse acoustique (5 kHz) et la nature lithologique des fonds marins

Sub-bottom profilers which were worked out in the sixty years did not first come into general use. These last few years, some new devices have been developed with most sediment penetration, which are to be more systematically used in sedimentological prospecting. After reviewing the sub-bottom profilers development, with laying stress on their originality, the different points of view of the interpretation are considered: layers geometry, lithological correlations, relations between the reflected picture and the depositional dynamics. In a bounded area, about 15 km², 90 bucket dredged samples and 12 core samples allowed a detailed mapping of the facies. This map is compared with different data from the seismic reflection investigation (5 kHz). A first approach concerns the distribution of some typical sismofacies selected on the whole seismic prospection. Thus five echotypes were picked out. By comparing, we can make a correlation between the character and surface feature of the sediment, and the corresponding seismic echo. In a second stage, the reflectivity change is considered in relation with the different sediment facies. The relative reflection coefficients are measured, either on the first peak, or on a longer time interval (1 ms), by integrating the seismic pulse. Both ways result in two maps of the relative reflection coefficient distribution.     

浅地层剖面交互拾取解释技术研究

浅地层剖面探测在海洋学研究与海洋工程调查中使用愈来愈频繁,剖面资料的解释工作变得越来越繁重。因浅地层剖面实际解释工作的需要,结合浅地层剖面资料的特点,研究并实现了剖面反射层位的自动拾取、利用Event号交互拾取特征点、等Ping间隔拾取、求取海底下反射层位厚度等解释功能,这些解释功能的实现加快了剖面解释工作的进度,提高了解释结果的精度,并在实际浅地层剖面资料解释工作中取得了良好的应用效果。     

An attenuation-based sediment classification technique using Chirp sub-bottom profiler data and laboratory acoustic analysis

A remote sediment classification technique based on attenuation measurements from Chirp sub-bottom profiler data is described. This differs from previously published work in that attenuation measurements are obtained for each stratigraphic unit within a complex, thinly interbedded sedimentary sequence. Compressional wave attenuation measurements are obtained for a wide variety of lithologies, including muds, silts, sands, clayey sands, silty clays and gravel lags, with grain sizes ranging from 8 Phi to -4 Phi. In addition, attenuation measurements from sub-bottom profiler data were calibrated against laboratory acoustic measurements of vibracores and seabed samples from corresponding geographic locations, under simulated in-situ conditions using a Pulse Tube method. We adapt an instantaneous frequency matching method using a causal attenuation filter to model the decay of the Chirp transmitted waveform. From this modelling, a relationship between t* (a causal attenuation operator) and change in instantaneous frequency is established. The Hilbert transform is used to extract instantaneous frequency information from Chirp seismic, which is used to derive attenuation information for selected individual stratigraphic layers imaged by the sub-bottom profiler. This paper draws attention to the limitations in comparing attenuation measurements derived from Chirp sub-bottom profiler data against previously published literature on experimental attenuation measurements, which are limited by the wide variance of these data, and the difficulty in finding a meaningful best fit to these data. This demonstrates the importance of calibrating remote sediment classification observations using complimentary acoustic analysis of seabed samples to generate a site-specific geoacoustic database. A positive correlation between laboratory and sub-bottom profiler attenuation measurements was obtained, with a correlation coefficient of 0.885. Poorly sorted gravels with a mixed lithic and biogenic pebble component are characterised by very high attenuation with values of Q from 4 to 19. These sediments are considerably coarser-grained than those typically described in previously published experimental studies.     

Design of a 3D Chirp Sub-bottom Imaging System

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz) that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with each hydrophone group containing four individual elements and a pre-amplifier. After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software aboard the acquisition vessel. The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface.     

PCPT资料在海底浅层砂土液化势判别中的应用

介绍了用PCPT资料判别浅层砂土液化势的方法,并分别用动三轴试验判别法和PCPT资料判别法比较了南海东部海域两个平台场址的浅层砂土液化势判别结果。通过实例验证说明,在熟练掌握 PCPT测试方法、资料采集、数据处理和成果解释的基础上,用PCPT判别法判别浅层砂土液化势是可行的。     

长江潮区界上界河槽浅层沉积结构探测研究

研究地层沉积结构是认识河流变迁历史的重要手段之一,潮区界作为河流物质和能量传输的关键界面之一,于2015年洪季,利用浅地层剖面仪对长江潮区界上界河段河槽浅地层结构进行了"覆盖式"探测。结果表明:长江潮区界上界河段河槽床面发育了大量沙波,尺度较大,陡坡明显朝向下游;崇文洲下游两侧水道中沙波发育较少,尺度也较小;浅层沉积结构显示该河段部分河槽床面以下存在4处不同形态的地质构造。     

基于浅地层剖面的海底浅表层沉积物物理性质参数反演技术研究

海底浅表层（小于1 m）沉积物的物理性质,如粒度、孔隙度、密度等是海洋沉积学研究和海洋工程地质分析的重要内容,目前主要基于有限的海底取样或原位测试获取这些沉积物的物理性质。浅地层剖面是基于声学信号（频率几千赫兹）在沉积物中的传播得到可反映沉积地层结构的数据,其中的一些声学参数,如海底反射系数、波阻抗等与沉积物物理性质密切相关。如何充分而有效地利用浅地层剖面资料,反演得到剖面覆盖区海底浅表层沉积物的物理性质参数,极具科学意义和应用价值,且基于声学属性反演沉积物物理性质是当前研究的热点。为此,本文基于渤海LD16-3CEPA至LD10-1PAPD路由段的浅地层剖面数据和海底表层沉积物的实测物理参数,利用Biot-Stoll模型建立研究区海底反射系数和沉积物物理性质之间的关系,并基于浅地层剖面数据计算得到的海底反射系数,反演了研究区海底浅表层沉积物的孔隙度、密度、平均粒径等物理性质参数。其中反演的孔隙度、密度、平均粒径与实测孔隙度、密度、平均粒径基本相符,偏差度基本都在20%的偏差范围内,表明该反演方法在该区的应用是可行的。     

水下井口探测技术研究

在海上油田开发过程中,往往存在一些当时不具备开发条件的水下井口。这些井口一方面现阶段具有重新开发价值,另一方面也是海洋工程建设的障碍物。而水下井口尺度小,常用的调查手段较难探测到。文中介绍了浅地层剖面仪和磁力仪的原理,并开展了浅地层剖面仪和磁力仪综合探测水下井口的应用与分析。结果表明浅地层剖面仪和磁力仪均可探测到井口,在浅地层剖面图像上表现为垂向的声学空白带,为桩坑和井口的反射;磁异常平面等值线为等轴状,存在极大值和极小值,井口位于极大值和极小值之间。浅地层剖面仪和磁力仪探测的井口位置相差1m,与给定井口坐标偏差2m,满足工程需求。因此使用浅地层剖面仪和磁力仪综合探测水下井口在现阶段不失为一种可行的方法。     

Elimination of Wind Wave Effects on Sub-Bottom Profiler Record

With the presence of wind waves, the swaying of survey vessel may effect the quality of sub-bottom profiler records and, therefore, it is necessary to correct the distortions induced by wave action. A major issue is to distinguish wind wave effect and real bedforms such as sand waves. In this paper, a bandstop filter is designed according to the frequency features of wind wave effect to treat the distortion of seabed topography by wind waves. The technique is used to correct the sub-bottom profile in order to eliminate the wave-induced distortions for the sub-bottom profile records from the Yangtze Estuary. This study shows that the undulate seabed record is resulted from wave action, rather than the presence of sand waves, and the filtration technique helps to eliminate the wave effect and recover the real morphology of seabed and the sediment sequence underneath. In addition, a method for data processing is proposed for the case that the record indeed represents a combination of wave effects and real bedforms.     

系缆式剖面测量平台的试验及分析

文章围绕测量平台的基本运动能力,介绍了一些平台固有特性的试验和理论分析,明确了这些特性对平台驱动力和阻力的作用,供有关人员参考交流。     

一种新型浅地层剖面仪试验平台的设计与应用

为探讨浅地层剖面声学影像形成原理,探索不同类型沉积物声学影像特征,厘清不同沉积物厚度的识别算法,采用模块化设计理念研发一套新型浅地层剖面仪室内试验平台。综合室内定位技术、浅剖试验平台尺寸合理性分析技术、直线轨道与换能器之间的固定连接技术和海底声学参数反演技术,形成一个试验高效的新型平台。通过铺设沉积物和布设障碍物,利用浅地层剖面仪进行走航测试,精确识别了沉积物的厚度和障碍物的位置。该平台可为开展理想环境下沉积物厚度和障碍物识别提供较好的测试环境,为声学海洋设备性能检测提供测试平台,也为高校学生和技术人员提供设备使用培训场所。     

A comparison of two Doppler current profilers

Two acoustic Doppler current profilers were tested in March 1988. The goal of the test setup was to compare two Doppler profilers under operational conditions in shallow waters. The two profilers involved were an RD-DR 1200 system and the profiler implementation on the Sonar Work Station of Rijkswaterstaat. In general, close correspondence was found between the two profilers, although under nonstationary current conditions large differences occurred. Water samples, taken at the test locations, have been analyzed with respect to mass concentration and particle size distribution. For some locations a poor correlation was found between these parameters and the received signal strength     

淤泥质海底航道边坡失稳滑塌声纹特征分析

边坡稳定是淤泥质海底航道安全运营的关键问题之一。海底航道边坡失稳滑塌过程的不同阶段浅地层剖面图像声纹特征不同。采用灰度共生矩阵和小波多尺度分解方法分析了航道边坡失稳滑塌过程浅地层剖面图像纹理特征。结果表明,对比度、能量、相关度和逆差距在边坡失稳滑塌过程中具有明显的差异,分别从不同方面刻画了浅地层剖面图像声纹的清晰度、纹理粗细、主要方向和规则性,以定量的形式显示其内在异质性。能量、相关度和逆差距的水平和垂直方向变化大于对角方向,水平方向波动最明显。浅地层剖面声强时间序列和垂向空间变化序列小波多尺度分解突出了声强变化的局部细节及其在各尺度上变化的强弱分布和突变点位置,克服了常规人工识读的困难,这些声纹特征是边坡失稳滑塌预测预警的重要依据,有助于对海底航道边坡稳定性的探测。     

海床浅表层硬质薄层的声学识别

由沉溺珊瑚礁、各类胶结砂以及胶结的珊瑚石或贝壳碎屑等组成的硬质薄层通常呈零散状分布,地质取样难以准确确定它们是如何分布的,这给海底管线施工带来极大的困难和风险。本文以南海北部为例,基于多种物探资料并结合正演模拟,分析、总结了海底以及海底之下硬质薄层的声学特征,在研究区综合识别出23个硬质薄层分布区。研究认为,硬质薄层与松散沉积物物理性质的差异可用于声学探测数据识别和定位。在浅地层剖面上,硬质薄层表现为强反射薄层,并对其下方地层的地震反射信号有一定的屏蔽作用,这一现象有助于确定硬质薄层是否存在以及其埋深和位置。在侧扫声呐影像和后向散射强度图上,硬质薄层通常表现为具有不规则形状的明暗变化阴影,阴影的边界指示了硬质薄层的分布范围。当硬质薄层出露于海底时,侧扫影像、反向散射强度结合浅地层剖面可以有效地识别并确定硬质薄层的范围;而当硬质薄层位于海床浅部（埋深数米到十几米）时,浅地层剖面可能是识别硬质薄层的唯一且最有效的方法。     

模糊层次分析法在浅剖数据质量评价中的应用

为解决浅剖数据质量评价指标不一、定量化不足的问题,本文基于层次分析法的原理,结合德尔菲法及模糊评价方法,建立了浅剖质量评价的模糊层次分析技术流程,构建了多层次的浅剖质量评价模型,确定了3个一级指标和14个二级指标,给出了各指标在质量评价中的定量权重,定出了4个质量评价等级。文章应用评价模型对深海及浅海两套浅剖数据集进行了评价,根据评价结果及最大隶属度原则,深海浅剖数据总体质量为中等,浅海浅剖数据总体质量为良好。结果显示,该模型可以有效地将专家主观经验以知识驱动的形式转成定量化评价指标,给出的评价结果客观、可量化,减少了数据质量评价过程中人为主观因素影响和片面性,可为数据进一步应用提供较为准确的应用等级建议。     

A high sinuosity,laterally migrating submarine fan channel-levee-overbank: results from DSDP Leg 96 on the Mississippi Fan,Gulf of Mexico

DSDP Leg 96 drilled four sites in a channel-levee-overbank system on the Mississippi Fan, Gulf of Mexico, approximately 300 km from the present Mississippi River Delta in water depths of about 2500 m (Sites 617, 620, 621 and 622). Apart from the uppermost 20–25 cm of Holocene marly foraminiferal ooze in most of the drilled sites, the entire cored intervals are in the Pleistocene Ericson Y Zone. Eight sedimentary facies are recognized: (1) biogenic oozes and muddy oozes; (2) calcareous muds; (3) clays and muds; (4) silty muds and muddy silts; (5) silt-laminated muds; (6) silts and sands; (7) muddy gravels and pebbly muds, and (8) gravels. Sediment accumulation rates on this part of the fan during the Wisconsin glaciation were as much as 11 m/1000 yrs, although most of the sediments probably accumulated from discrete, geologically instantaneous events. Site 621 and Site 622 are located within a prominent channel, Site 617 on an adjacent levee, and Site 620 in overbank deposits approximately 18 km northeast from the channel sites. In this part of the fan, there is one prominent high sinuosity channel, asymmetric in cross section and flanked by levees with probable ridge-and-swale topography. Near these drill sites, the channel width is 3–4 km and its bathymetric relief ranges from 25–45 m. Downfan, the dimensions of the channel decrease. Site 617 (to 191.2 m sub-bottom) and Site 620 (to 422.7 m sub-bottom) mainly comprise fine-grained, thin-bedded turbidites, with Site 617 tending to be slightly coarser grained and showing considerably more evidence of wet-sediment deformation. Site 621 (to 214.8 m sub-bottom), in the channel axis near the deepest part of a meander, contains mainly muds with a downhole increase in the silt content above 195 m sub-bottom, where pebbly muds overlie clean gravel that was obviously washed during core-retrieval and probably was a sandy gravel or gravelly sand. Site 622 (to 208 m sub-bottom) shows similar lithologies to Site 621 although the sediments generally contain more silt, and towards the base of the hole become thoroughly laminated silts and sandy silts: pebbles within muds and silts occur at 199 m sub-bottom. Based on overall grain size trends over tens of metres, the channel sites show ill-defined fining-upward sequences, whereas the levee and overbank sites show coarsening-upward sequences, although the upper part of Site 617 is a fining-upward sequence. Biogenic components of sediments at the channel sites are dominated by shallow-water benthic foraminifera derived from the continental shelf, with the coarser grained clastic intervals containing reworked late Cretaceous planktonic foraminifera and radiolaria from the Upper Mississippi River Valley. The levee and overbank sites have a larger percentage of Quaternary radiolaria, pelagic algal cysts, and more planktonic foraminifera than the channel sites. Seismic reflection profiles across this most recent fan channel show high-amplitude reflectors in the lower part of the channel fill, thought to correspond to the coarsest grained channel lag deposits. Isopach maps show that the lag deposits are up to 6.5 km wide, slightly more than 200 m thick, and that the northernmost meander belt has migrated about 2 km laterally, 1.2 km downfan, and has climbed 175 m stratigraphically (Kastens and Shor, 1985; Sterling et al., 1985). Evolution of the meander belt shows features common to point-bar migration in high sinuosity fluviatile systems. While the location of Sites 617, 620, 621 and 622 have been drilled within a middle fan environment, the width/depth ratios and the fact that this channel is a single conduit in this part of the fan, perhaps suggest a more appropriate comparison with many inner or upper fan environments that have been described in the literature.