CAREER: Development of a broadband acoustic system for quantifying the flux of free gas in methane seeps

在这份CAREER提案中，PI要求资助开发一种宽带声学系统，以量化甲烷渗漏中与深度相关的气泡大小分布和气体空隙率，并测量甲烷气体从海底逸出并通过水柱上升的通量。这些量的声学测量反演将通过观察气泡在宽频率范围内（1-100 kHz）的响应来利用气泡的机械共振。声学系统将在其大部分频率范围内（10-100 kHz）采用恒定波束宽度换能器，以便准确地处理空间接近的不同大小分布的气泡羽流，正如有时观察到的那样。该系统将被设计成集成到深水远程操作车辆（ROV）中，并在全海洋深度工作。将建立第二种操作模式，将该系统从机遇号船上拖走，作为更快速、更大规模声学调查策略的一部分。宽带声学系统的开发和使用可以直接解决关于海底逸出的甲烷气泡的命运和演化的假设。使用拟议的系统有可能提供变革性的结果，包括1)对从海底逸出的全球甲烷通量的精确估计，2)对海洋作为甲烷汇的能力的进一步了解，以及3)对从海底渗漏到达大气的全球甲烷通量的估计。提议的仪器提供的数据可能对更广泛的科学界有相当大的好处。人们认为甲烷渗漏会影响海洋化学、海洋微生物生命和大气化学，对海洋生产力、大气辐射平衡和古气候研究产生影响。关于这些渗漏的基本信息是缺乏的，而提出的仪器可以为填补我们理解中的这一漏洞做出重大贡献。一些本科生和研究生将从帮助开发和测试一种新设备的经验中受益。让本科生为学校的回声探测仪套件做开发工作的想法非常好。外联部分将覆盖当地几所学校的学生，并得到当地教师和新罕布什尔海洋基金的书面支持。与工业界、Sea Grant和其他机构的合作提供了证据，证明该项目将具有广泛和持久的影响，并且被许多其他科学家认为是一个重要的问题和解决问题的好方法。

In this CAREER proposal the PI requests funding to develop a broadband acoustic system to quantify the depth dependent bubble size distribution and gas void fraction in methane seeps, and to measure the flux of methane gas escaping the seabed and rising through the water column. Inversion of acoustic measurements for these quantities will exploit the mechanical resonance of bubbles by observing the bubbles response at a wide range of frequencies (1-100 kHz). The acoustic system will employ a constant beamwidth transducer for much of its frequency range (10-100 kHz) in order to accurately treat bubble plumes with different size distributions that are in close spatial proximity, as is sometimes observed to happen. The system will be designed to integrate into a deepwater remotely operated vehicle (ROV) and to function at full ocean depth. A second operational mode will be established where the system can be towed from a ship of opportunity as part of a more rapid, wide-scale acoustic survey strategy. The development and use of a wideband acoustic system can directly address hypotheses about the fate and evolution of methane gas bubbles escaping the seabed. The use of the proposed system has the potential to provide transformative results including 1) refined estimates of the global flux of methane escaping the seabed, 2) increased understanding of the oceans capacity as a methane sink, and 3) estimates of the global flux of methane reaching the atmosphere from seabed seeps.Broacer ImpactsThe data provided by the proposed instrument could be of considerable benefit to the wider scientific community. Methane seeps are thought to affect ocean chemistry, ocean microbial life and atmospheric chemistry, with consequences for ocean productivity, radiation balance in the atmosphere and paleoclimate studies. Basic information on these seeps is lacking, and the proposed instrument could make a significant contribution to plugging this hole in our understanding. Several undergraduate and graduate students would benefit from the experience of helping with the development and testing of a novel device. The idea of having undergraduates do the development work for the schools echo-sounder kit is excellent. The outreach component would reach the pupils at several local schools, and has the written support of both local teachers and the New Hampshire Sea Grant. The collaborations with industry, Sea Grant, and other agencies provides evidence that the project will have a wide spread and lasting impact and that it is perceived by many other scientists as an important problem and a good approach to the problem.