深海热液/冷泉远距离探测和定位机理研究

Hydrothermal vent (HDTV) and cold seep (CS) in deep sea emits gaseous substances such as Hydrogen sulphide, methane and CO2. The most advanced technology available to-date for the localisation of cold seep and hydrothermal vents in the ocean has been limited to close contacting method within very short ranges of a few meters. This is a fundamental research about the remote sensing of gas bubbles in the deep sea environment and simultaneously to diagnose chemical compositions of gas contents inside the bubbles, at stand off detection ranges of 0.1-1km, to understand the origins of the gas bubbles whether they are emitted from the cold seep/hydrothermal vent or from other sources not relevant to hydrate resources. The sole objective of the research is to explore whether electro-optical and acoustic techniques are sensitive enough to locate, and simultaneously to probe the chemical composition of the emitted gas, in hazardous condition of the deep sea environment. This study formulates a world-first attempt in ocean research, by exploiting the phase and scattering phenomena of photons and acoustic wave, to locate the CS and HDTV resources remotely for the very first time. This is an extreme challenge research project, hence the research will be conducted through joint efforts of Hangzhou Dianzi University and the Cranfield University in the UK. .The propose techniques are termed as Phase Contrast Sonic imaging(PCSI) and Differential Reflection Lidar Raman (DIRLIR), which have potentials for the detection of gaseous substances in liquid such as bubbles in blood, turbulence of sea wakes due to ships and submarines, hydrate detection and oil/methane mining from ocean.

深海热液和冷泉溢出气体成分主要包括H2S、CH4和CO2等。目前深海热液和冷泉的近距离接触式探测方法的探测距离不超过几米。本项目研究并在海洋研究领域首次提出"相衬声波成像技术(Phase Contrast Sonic imaging，PCSI)和差分反射激光雷达拉曼技术(Differential Reflection Lidar Raman，DIRLIR)"声学-光电组合探测技术，利用声波探测、反射光相位和偏振改变、以及拉曼识别，对海水中气泡进行远距离探测，从而实现对深海热液和冷泉的远距离探测和定位，最大探测距离达1km；同时，该技术还可对气泡内的气体成分进行识别，从而判断这些气泡是由深海热液/冷泉溢出，还是源于其他与甲烷资源无关的气体源。此外，本技术还可用于探测液体中包含气体成分的其他场合，如血液中的气泡、由于船舶和潜器运动造成的海水湍流尾迹、海洋石油/天然气勘探、海底石油管道泄漏等。

目前，海洋热液/冷泉探测研究已经成为海洋研究的热点。根据海洋热液/冷泉活动区喷口都有气泡溢出这一物理特征，本项目简化研究思路，将海洋热液/冷泉的探测转化为水下气泡的探测研究。项目主要研究内容包括：.（一）气泡声学探测技术研究.1、通过水声探测实验验证了水下气泡的共振频率，总结了水下气泡的反演模型、反射截面和反射强度等特点；分析了水下气泡群的声学信号特性及散射特性；.2、结合理论计算结果，设计搭建了气泡光学探测实验平台；.3、采用声波透射方法，对水下气泡进行了透射声波实验，得到了声波的透射声压幅值和气泡流量的关系式，实现了水下气泡流量计算；采用信号互相关分析方法，实现了气泡上升速度计算，为热液/冷泉区气泡流量、流速的探测提供了新的方法和思路；.4、采用最小二乘法定位原理，对水下目标进行了声学探测定向/定位研究；依据水下目标回波亮点模型，建立了刚性小球的三维散点声图像和柔性气球的二维轮廓图，重构出了水下刚性和柔性目标的特征；实验结果表明，目标回波亮点模型可以为声纳目标识别等方面的研究提供支持。.（二）气泡光学探测技术研究.1、基于Mie散射理论，通过matlab编程计算，获得单个气泡的光学效率因子以及散射光强度的分布，从理论上证明了通过探测气泡后向散射光的方法来探测气泡的可行性；.2、结合理论计算结果设计搭建实验平台。通过开孔反光镜的设计和黑色吸光布的布置，最大可能地减少光线的干扰，优化实验效果；.3、改变探测距离，得出散射光强度与探测距离之间的关系；根据光散射角度分布的理论计算结果,对临界角附近的散射光进行探测，确定临界角的位置。.通过气泡声学探测和光学探测技术研究，实现了对水下气泡的远距离识别，进而实现对热液和冷泉的远距离识别。此外，本技术还可用于探测液体中包含气体成分的其他场合，如血液中的气泡、由于船舶和潜器运动造成的海水湍流尾迹、海洋石油/天然气勘探、海底石油管道泄漏等。