Study on visual control system of acoustic in situ measurement technology for survey of seafloor sediment

Abstract

A new kind of visual acoustic measurement system was developed to obtain the acoustic characteristics of seabed sediment and the working state of in situ measuring equipment in real time. The control unit of the system structure is mainly made up of the underwater control unit and the deck control unit. In comparison with similar traditional systems, the system can transmit the working video image, the measured acoustic data and the waveform synchronous from the underwater control equipment to the deck control unit through the connecting cable. Apart from self-contained in situ measurement, the working modes of it include visual online real-time control. In order to guarantee the stability and measurement precision of the video control system, the process control of in situ measurement was strictly tested in the experimental tank. In 2017, sea trials of the in situ measurement system was carried out in the South China Sea. In the process, data related to measurement, including the acoustic velocity and attenuation coefficient of the seabed sediment, were obtained as well. The results from sea trials show that the control process of the visual system is intuitive, reliable and accurate, and therefore it can be popularized and applied.     

海底沉积物取样扰动的有限元研究

应用非线性有限元分析方法,对管状取样器取样过程中的沉积物扰动状况进行了研究.建立了取样管与沉积物接触的二维轴对称有限元模型.重点分析了取样时取样管内沉积物的变形、应力和应变状况.有限元分析结果表明了取样管贯入过程中沉积物应力、应变均产生了变化,扰动显著.证实了工程实际中取样所造成的沉积物样品原始层序混杂或弯曲变形、长度缩短等扰动的后果.海底沉积物的低扰动取样样品对于诸多海洋科学研究非常重要.     

海底重力取样技术的探讨

对重力取样器的用途、使用及相关技术进行了较全面的介绍,尤其介绍取样作业中的一些实际经验,对该取样器的技术特点、相关技术和未来发展方向进行深入的探讨。     

浅海底瞬变电磁探测技术研究新进展

瞬变电磁法应用于浅海底进行资源勘探或工程地质勘查时,需要将仪器系统和观测装置置于海底,以克服海水屏蔽效应。因此,要求能够远程控制仪器进行自动化数据采集;同时,受工作环境影响,需要将观测装置小型化;另外,通过拖曳式测量提高工作效率。总结课题组目前的研究成果,就仪器系统研制、观测装置小型化、拖曳式测量及海水影响等内容的研究进展进行了简要叙述。     

Assessment of Impact on Seafloor Features in INDEX Area

Abstract

Observations on seafloor features from subbottom profiling and seabed photography data show that the undisturbed and natural conditions before the benthic disturbance undergo a substantial change after operation of the disturber. The effects can be seen in the form of deep trenches and grooves, formed by the action of the sleds and the pumping of the sediment along its path, as well as sediment piles on either side of the track. Biological traces such as fecal coils, casts, tubes, burrows, and trails get obliterated in the areas of disturbance and resedimentation. The smooth, uniform nature of the seafloor observed in pre-disturbance phase shows microtopographic changes in and around the disturbed area as a result of sediment excavation and resettlement. Vertical mixing as well as lateral transport of sediment alter the geological, biological, physical, and chemical conditions on the seafloor, which need to be monitored over time to assess the process and the time taken for restoration of environmental conditions.     

Late amagmatic extension along the central and eastern segments of the West Philippine Basin fossil spreading axis

The spreading processes within the West Philippine Basin (WPB) remain partly unknown. This study presents an analysis of the tectono-magmatic processes that happened along its spreading axis during the conclusion of the last spreading phase at 33/30 Ma. We demonstrate that the late episode of N-S opening from an E-W-trending spreading system has been followed by a late tectonic event occurring in the central and eastern parts of the basin. This event was responsible for transtensional strain accommodated along the NW-SE faults cutting through the former E-W rift valley in the central part of the basin. In its eastern part, the same event occurred at a larger extent and led to the creation of a new NW-SE axis, obliquely cutting the older E-W spreading segments and their associated spreading fabrics. At this location, several tens of kilometers of slightly oblique amagmatic extension occurred following a ∼60° direction. We propose that this late event is associated with the onset of E-W opening of the Parece-Vela Basin located along the eastern border of the WPB at 30 Ma. Extensive stresses within this basin were probably transmitted to the hot and easily deformable rift zone of the WPB. The newly-created NW-SE axis most likely propagated from east to west, being responsible for scissors opening within the WPB. NE-SW extension ceased when well-organized spreading started at 26 Ma in Parece-Vela Basin, accommodating entirely the global extensive stress pattern.     

Processing Multibeam Backscatter Data

A new highly precise source of data has recently become available using multibeam sonar systems in hydrography. Multibeam sonar systems can provide hydrographic quality depth data as well as high-resolution seafloor sonar images. We utilize the seafloor backscatter strength data of each beam from multibeam sonar and the automatic classification technology so that we can get the seafloor type identification maps. In this article, analyzing all kinds of error effects in backscatter strength, data are based on the relationship between backscatter strength and seafloor types. We emphasize particularly analyzing the influences of local bottom slope and near nadir reflection in backscatter strength data. We also give the correction algorithms and results of these two influent factors. After processing the raw backscatter strength data and correcting error effects, we can get processed backscatter strength data which reflect the features of seafloor types only. Applying the processed backscatter strength data and mosaicked seafloor sonar images, we engage in seafloor classification and geomorphy interpretation in future research.     

现代海底的成矿作用与矿产资源

迄今所发现的现代海底成矿作用主要分布在沿大西洋中脊、东太平洋海岭和西太平洋沟弧盆系的各热液田中。现代海底成矿作用形成了大量具有重大经济意义的矿产,它们主要是铁锰结核、富钴结壳、多金属硫化物和被称之为２１世纪能源的气体水合物。现代海底成矿作用及其所形成矿床的研究是矿床前研究的前沿课题,它对于矿床学的发展,揭示成矿作用的奥秘和海底资源的开发都具有重大意义。     

现代海底热液成矿作用

从现代块状硫化物矿床成矿特征对比角度,总结分析了世界现代海底喷流的块状硫化物成矿堆积,综述了现代海底块状硫化物成矿主要形成于洋壳和岛弧环境的实际观察结果,突出强调了洋壳环境和岛弧或陆壳环境两种成矿环境对成矿类型分类的意义。对上地幔部分熔融岩浆来源与地壳物质可能带人、火山喷发岩浆系列的演化和对热液成矿作用的控制进行了讨论,对比分析了岩浆流体对成矿的重要贡献和控制作用,以及成矿热液循环体系形成的条件和模式。     

A convection-conduction model for analysis of the freeze-thaw conditions in the surrounding rock wall of a tunnel in permafrost regions

The results of simulated tidal current field, wave field and storm-induced current field are employed to interpret the depositional dynamic mechanism of formation and evolution of the radial sand ridges on the Yellow Sea door. The anticlockwise rotary tidal wave to the south of Shandong Peninsula meets the following progressive tidal wave from the South Yellow Sea, forming a radial current field outside Jianggang. This current field provides a necessary dynamic condition for the formation and existence of the radial sand ridges on the Yellow Sea seafloor. The results of simulated “old current field (holocene)” show that there existed a convergent-divergent tidal zone just outside the palaeo-Yangtze River estuary where a palaeo-underwater accumulation was developed. The calculated results from wave models indicate that the wave impact on the topography, under the condition of high water level and strong winds, is significant. The storm current induced by typhoons landing in the Yangtze River estuary and turning away to the sea can have an obvious influence, too, on the sand ridges. The depmitional dynamic mechanism of formation and evolution of the radial sand ridges on the Yellow Sea seafloor is “tidal current-induced formation—storm-induced chang—tidal current-induced recovery”. Project supported by the National Natural Science Foundation of China (Grant No. 49236120).