Collaborative Research: Ocean Remote Sensing Using Ambient Noise

智力优势：近年来，理论上已经证明，在非常弱的假设下，可以通过计算位置A和B的环境噪声的同时测量的互相关来提取声学格林函数G(A，B，t)的良好近似值。G(A，B，t)是位置A对位置B的脉冲点源的响应；通过静态环境中的倒数G(A，B，t)=G(B，A，t)。这一过程有时被称为噪声干涉测量。噪声干涉测量的实用价值已经在包括地震应用在内的各种环境中得到了证明。由于这项技术不涉及使用主动声源，它只需要非常有限的实验资源。本项目旨在论证噪声干涉测量在海洋中的可行性，并探索与理解噪声干涉测量在海洋遥感中的局限性相关的几个问题。这项工作包括实验、数据分析、理论和数值模拟相结合。预计这将为使用噪声干涉测量法作为海洋内部声学遥感的一种实用手段提供基础，为此，重点将放在使用真实的海洋数据来证明该方法在实际海洋条件下的实用性，而不是理想化的模拟。更广泛的影响：拟议的工作已应用于几个具有明显社会效益的领域。这些包括用于诊断和监测目的的非侵入性医学超声，以及对结构的非破坏性评估，例如，仅使用交通产生的振动来检测桥梁中的裂缝。除了开发了解和解决这些问题的工具外，该项目还将支持和培训两名研究生。对于海洋遥感，利用环境声遥感海洋体积的能力消除了用活跃的声源损害海洋生物的可能性。这项工作将在松散的、没有资金的情况下与一小群俄罗斯科学家合作完成，从而为加强国际联系做出贡献。

Intellectual Merit: In recent years it has been shown theoretically that, under very weak assumptions, a good approximation to the acoustic Green's function G(A, B, t) can be extracted by computing the cross-correlation of simultaneous measurements of ambient acoustic noise at locations A and B. G(A, B, t) is the response at location A to an impulsive point source at location B; by reciprocity G(A, B, t) = G(B, A, t) in a quiescent environment. This procedure is sometimes referred to as noise interferometry. The practical utility of noise interferometry has been demonstrated in a variety of settings, including seismic applications. Because this technique does not involve the use of active acoustic sources, it requires only very modest experimental resources. This project seeks to demonstrate the feasibility of noise interferometry in the ocean, and explore several issues relevant to understanding the limitations of noise interferometry for ocean remote sensing. The work involves a combination of experiment, data analysis, theory and numerical simulations. It is anticipated to provide a foundation for using noise interferometry as a practical means of acoustic remote sensing of the ocean's interior, and to that end the focus will be on using real ocean data to demonstrate the utility of the method under practical ocean conditions, rather than such things as idealized simulations. Broader Impacts: The proposed work has applications to several fields with obvious societal benefits. These include noninvasive medical ultrasound for diagnostic and monitoring purposes, and nondestructive evaluation of structures, e.g., crack detection in bridges using only traffic-generated vibrations. In addition to developing the tools to understand and address these problems, the project will support and train two graduate students. For ocean remote sensing, the ability to use ambient sound for remote sensing of the ocean volume eliminates the possibility of harming marine life with active sound sources. The work will be done in loose, unfunded collaboration with a small group of Russian scientists, thereby contributing to the strengthening of international ties.