EAGER: Development of a Prototype 2D Acoustic Tomography System for Rapid Temperature Measurements in Diffuse Hydrothermal Effluent

EAGER：开发用于快速测量扩散热液流出物温度的原型 2D 声学层析成像系统

• 批准号: 1744255
• 负责人: Eric Mittelstaedt
• 金额: $ 5.18万
• 依托单位: Regents of the University of Idaho
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-15 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1744255&HistoricalAwards=false
• 关键词: EAGER; Development; Prototype; 2D; Acoustic

Mid-ocean ridges, the boundaries between separating tectonic plates, are some of the most volcanically active features on Earth. Along many ridges, storage of molten magma in shallow chambers results in heating of seawater stored in the porous crust. Thermally buoyant, this seawater rises through the crust, is chemically altered by water-rock interactions, and finally exits the seafloor at hydrothermal vents. It is now recognized that this type of deep-sea hydrothermal circulation plays a key role in controlling long-term ocean chemistry, the thermal and chemical structure of the oceanic crust, and the evolution of unique and diverse chemosynthetic ecosystems found nowhere else on the planet. However, quantifying the biological and chemical impact of hydrothermal circulation requires knowledge of the volume, heat, and chemical fluxes exiting the seafloor, which are notoriously difficult to quantify. One large source of uncertainty in flux estimates lies in the widespread distribution of lower-temperature (/=100°C) diffuse hydrothermal fluids, which are commonly transparent and escape through fractures, porous rock, and sediment. It is estimated that diffuse fluids contribute more to the heat and volume fluxes of hydrothermal systems than higher temperature (300°C), "black smoker" style vents. Existing methods to quantify the flux of diffuse hydrothermal venting are limited by small measurement areas, measurements of a single quantity (e.g., only temperature or only velocity), or are invasive and alter the flow as they measure it. This project will develop new technologies for improved measurement of diffuse venting. Researchers will collaborate with University of Idaho, School of Engineering undergraduate students as part of their senior year Capstone Design Course to develop a prototype two-dimensional (2D) acoustic tomography system that can rapidly measure the temperature of anomalously warm, upwelling diffuse fluids across a ~1 m2 area. Development of these technologies will lead to future construction of a deep-sea measurement system targeting diffuse hydrothermal venting.The primary goal of this project is to develop a prototype two-dimensional (2D) acoustic tomography system capable of a time series of rapid (1 Hz) measurements of the temperature of anomalously warm, upwelling fluids at a spatial resolution of centimeters across a ~1 square meter area. The proposed system will consist of ~20-25 acoustic immersion transducers fixed at known spacing on a square, rigid frame. A subset of the transducers (~4-6) will emit staggered acoustic chirp pulses and the system will measure the pulse travel time between the emitting and receiving transducers. Using travel-time acoustic tomography, these travel times will be converted to sound speed and finally temperature throughout the 2D domain. Development will begin with a two-transducer, 1D system to test appropriate signal frequencies (e.g., kHz or MHz), chirp type (increasing or decreasing frequency), transducer shapes (e.g., spherical, planar, cylindrical), and effective measurement rates. Building upon these results, the final prototype will utilize the optimum transducer shape and pulse frequencies. After construction, the system will undergo submergence tests at the University of Idaho with controlled sources of warm, buoyantly rising fluids. To calculate fluid temperatures, we will evaluate several travel-time inversion methods including the algebraic reconstruction technique (ART), multiplicative algebraic reconstruction technique (MART), and simultaneous iterative reconstruction technique (SIRT). Final results will be compared to thermocouple measurements distributed throughout the 2D measurement domain.

中山脊，分离构造板之间的边界是地球上最有活跃的火山活动特征。沿着许多山脊，在浅室中熔融岩浆的储存导致储存在多孔外壳中的海水加热。热浮力，这种海水从地壳上升起，被水摇滚相互作用化学改变，最后从水热通风孔出发了海底。现在已经认识到，这种类型的深海水热循环在控制长期的海洋化学，海洋壳的热和化学结构以及独特而多样的化学合成生态系统的演变中起着关键作用。但是，量化水热循环的生物学和化学影响需要了解出现海底的体积，热量和化学通量，众所周知，这些通量难以量化。通量估计的一种不确定性的一个很大的不确定性来源在于低温（/= 100°C）弥漫性热液流体的宽度分布，通常是透明的，并通过裂缝，多孔岩石和沉积物逃脱。据估计，与更高温度（300°C）（“黑人吸烟者”风格的通风孔相比，弥漫通量对热液系统的热量和体积通量更大。量化扩散氢气通量通量的现有方法受到小测量区域的限制，单个量的测量值（例如，仅温度或仅速度），或者是侵入性并在测量时改变流量。该项目将开发新技术，以改善弥散排气的测量。研究人员将与爱达荷大学（University of Idaho），工程本科生合作，作为其高年级顶峰设计课程的一部分，以开发一种原型二维（2D）声学断层扫描系统，该系统可以快速衡量〜1平方米的异常温暖，上升，上升的扩散液的温度。这些技术的开发将导致未来的深海测量系统靶向弥漫性氢气。所提出的系统将由〜20-25个固定在正方形的刚性框架上的已知间距上的声音浸入式传感器组成。换能器的子集（〜4-6）将发出交错的声音chirp脉冲，系统将测量发射和接收传感器之间的脉冲行进时间。使用旅行时间的声学断层扫描，这些旅行时间将转换为声速，最后在整个2D域中温度。开发将从测试适当的信号频率（例如KHz或MHz），CHIRP类型（增加或降低频率），换能器形状（例如球形，平面，平面，圆柱形，圆柱形）和有效测量率的两种透射器1D系统开始。在这些结果的基础上，最终的原型将利用最佳的传感器形状和脉搏频率。施工后，该系统将在爱达荷大学接受淹没测试，并受控温暖，浮动的液体来源。为了计算流体温度，我们将评估几种旅行时间反演方法，包括代数重建技术（ART），乘法代数重建技术（MART）和简单的迭代重建技术（SIRT）。将最终结果与分布在2D测量域中的热电偶测量进行比较。