Collaborative Research: Quantitative Estimates of Oceanic Turbulence and Temperature Structure from Seismic Reflection Data

合作研究：根据地震反射数据定量估计海洋湍流和温度结构

• 批准号: 0647573
• 负责人: Raymond Schmitt
• 金额: --
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0647573&HistoricalAwards=false
• 关键词: Collaborative; Research; Quantitative; Estimates; Oceanic

OCE-0647573Recent work by our group shows that oceanic finestructure can be imaged in great detail usinglow-frequency (10-150 Hz) seismic reflection profiling, a technique that is widely used to image the solid earth but until recently has not been systematically applied to studies of oceanic internal structure. These findings open up a new field of endeavor in physical oceanography, which we call "seismic oceanography" (SO). Development of this new technique into a tool that can produce useful (and trusted) information on dynamical properties of interest to physical oceanographers is entering a critical stage. Much progress has been made in the first three years of effort. We have achieved a basic physical understanding of the origin of low-frequency acoustic reflections in the ocean. Our group and others have produced fascinating images of finestructure in numerous settings, including fronts, Meddies, intrathermocline lenses, warm-core rings, water-mass boundaries, and thermohaline staircases, some of which raise unexpected questions about the processes controlling the distribution of oceanic finestructure. We have shown that information on internal-wave spectra and temperature contrasts can be gleaned from seismic data. Yet despite these early successes, there remains considerable uncertainty about the extent to which (and under what circumstances) useful, reliable, quantitative information can be gleaned from seismic data. Seismic oceanography has yet to find its niche. In this study funds are requested for development and application of new SO analysis techniques that will help determine that niche. We will address two fundamental questions: (1) What quantitative information about dissipation, internal waves, and temperature structure can be gleaned from seismic images of finestructure? (2) What are the limitations and uncertainties of the method? Preliminary results are promising. A new theory of horizontal wavenumber (kx) spectra of isopycnal slopes suggests that seismic reflection images may be especially well suited to estimating turbulence dissipation, as the turbulent subrange of kx spectra extends to surprisingly large horizontal scales (100 m), which are easily imaged seismically. Our calculations show that reasonable estimates of turbulence dissipation can indeed be derived from seismic images. Our preliminary tests of full-waveform inversion to SO data shows that typical temperature finestructure can be resolved by seismic data at commonly acquired frequencies, though uncertainties are currently poorly characterized. We propose to undertake continued method development and apply these techniques to about a dozen publicly available legacy seismic data sets, from a variety of oceanic environments. Fully processed images on ~20 seismic sections, estimate dissipation from kx spectra, and invert seismic waveforms to estimate temperature profiles will be produced by comparing our results to ground-truth control from coincident XBT/CTD information.Intellectual Merit: We are in the formative stages of developing what may become a very useful tool for imaging oceanic finestructure. Preliminary work shows that this tool can provide unique information on turbulence dissipation that may help improve our ability to measure oceanic mixing and map "hotspots" of mixing. The work proposed here will advance seismic oceanography to a more quantitative state and therefore is a logical next step in determining the capabilities and limitations of low-frequency acoustic imaging in study ocean structure and dynamics.Broader Impacts: This study will develop a new approach for imaging ocean structure anddynamics, which exert a major control on the Earth's climate. Our study will have implications for understanding such processes as ocean mixing and the distribution of heat and salt in the ocean's interior. Our work serves NSF's broader goals in numerous ways that go beyond the specific realm of increasing physical oceanographic knowledge. Specifically, we will (1) advance a new cross-disciplinary field to the improvement of both marine geology and geophysics and physical oceanography; (2) help train a new cadre of graduate students and postdocs in this rapidly developing field; (3) involve an undergraduate student in cutting-edge research; and (4) support gender diversity in science, by training two female students.

我们小组最近的工作表明，可以用低频（10-150 Hz）地震反射剖面法对海洋精细结构进行非常详细的成像，这种技术被广泛用于固体地球成像，但直到最近才被系统地应用于海洋内部结构的研究。这些发现开辟了物理海洋奋进的一个新领域，我们称之为“地震海洋学”（SO）。将这一新技术发展成为一种工具，能够提供物理海洋学家感兴趣的动力特性方面的有用（和可信）信息，目前正进入一个关键阶段。在头三年的努力中取得了很大进展。我们已经对海洋中低频声反射的起源有了基本的物理认识。我们的团队和其他人已经在许多环境中产生了迷人的精细结构图像，包括前线，Meddies，温跃层内透镜，暖核环，水团边界和温盐阶梯，其中一些提出了意想不到的问题，控制海洋精细结构的分布过程。我们已经表明，可以从地震数据中收集有关内波频谱和温度对比的信息。然而，尽管这些早期的成功，仍然有相当大的不确定性，在何种程度上（在什么情况下），有用的，可靠的，定量信息可以从地震数据收集。地震海洋学尚未找到自己的定位。在这项研究中，要求提供资金，用于开发和应用新的SO分析技术，这将有助于确定该利基。我们将解决两个基本问题：（1）从精细结构的地震图像中可以收集到关于耗散、内波和温度结构的什么定量信息？(2)该方法的局限性和不确定性是什么？初步结果是有希望的。一个新的理论水平波数（KX）谱的等密度线斜率表明，地震反射图像可能特别适合于估计湍流耗散，作为湍流子范围的KX谱扩展到令人惊讶的大水平尺度（100米），这是很容易成像地震。我们的计算表明，合理的估计湍流耗散确实可以从地震图像。我们对SO数据进行的全波形反演的初步测试表明，典型的温度精细结构可以通过地震数据在通常采集的频率下解决，尽管目前的不确定性很差。我们建议进行持续的方法开发，并将这些技术应用于来自各种海洋环境的十几个公开可用的遗留地震数据集。通过比较我们的结果与来自一致XBT/CTD信息的地面实况控制，将产生在~20个地震剖面上的完全处理的图像，从kx谱估计耗散，并反演地震波形以估计温度剖面。智力优点：我们正处于开发可能成为成像海洋精细结构的非常有用的工具的形成阶段。初步工作表明，该工具可以提供有关湍流耗散的独特信息，有助于提高我们测量海洋混合和绘制混合“热点”的能力。这里提出的工作将推进地震海洋学到一个更定量的状态，因此是一个合乎逻辑的下一步，在确定的能力和局限性的低频声学成像在研究海洋结构和dynamics.Broader影响：这项研究将开发一种新的方法来成像海洋结构anddynamics，施加一个主要的控制地球的气候。我们的研究将对理解海洋混合以及海洋内部热量和盐的分布等过程产生影响。我们的工作以多种方式服务于NSF更广泛的目标，超越了增加物理海洋学知识的具体领域。具体而言，我们将（1）推进一个新的跨学科领域，以改善海洋地质学和海洋物理学以及物理海洋学;（2）帮助在这个快速发展的领域培养一批新的研究生和博士后;（3）让一名本科生参与尖端研究;（4）通过培养两名女学生来支持科学领域的性别多样性。