Sediment Imaging with Autonomous Underwater Vehicles: A Community Tool

地球海洋的最深处是遥远而难以探索的。因此，在那里发生的地质、生物和化学过程仍然知之甚少。在过去的十年里，自主水下航行器（AUV）技术的进步意味着我们现在可以把这些航行器送到几英里深的海底，在那里它们从海底上方收集数据。auv通常配备高分辨率压缩高强度脉冲（CHIRP）声纳，可以捕获覆盖海底的沉积物的厘米级分辨率横截面图像。这些厚度可以作为一个特征暴露在海底的时间长度的代表。尽管有这种潜力，但时间限制和缺乏容易获得的声纳数据处理方案意味着这些CHIRP数据通常未得到充分利用。本研究开发了一个标准的工作流程和软件，用于处理EdgeTech CHIRP声纳数据，用于海上和岸上，使用已经存在的auv从大西洋中脊的特定位置获取的沉积物CHIRP调查和其他相关成像数据。处理后的数据将用于测量某一地区的沉积物厚度，在该地区，对该参数的了解有助于我们了解中洋脊轴线上的断层和火山作用之间的相互作用。该研究的广泛影响增加了现有美国AUV舰队的价值和能力，并推进了我们对洋中脊地壳形成的理解。这项工作的方法和成果将被纳入高度多样化的圣地亚哥联合学区在职教师的专业发展研讨会，为整个学校系统广泛使用的课程提供资源，并为早期职业调查员提供支持。在远离陆地来源的地区，深海海洋环境中的沉积物厚度是一个特征暴露在海床上的时间的粗略代表。因此，这提供了一种限制地质事件（如火山爆发和/或断层滑动）发生时间的方法。在年轻的特征，如洋中脊轴向山谷，沉积物通常只有几米厚，因此无法被其他船上的地球物理/地震成像工具所捕获。目前，这些沉积物的厚度只能通过水下航行器携带的近底声纳来成像。这些工具的使用在缓慢扩张的洋中脊特别有用，在那里，人们对低角度断层（称为分离）与火山作用之间的相互作用知之甚少。虽然现在很清楚，大片的海底区域是在剥离断层的影响下形成的，但剥离与岩浆活动和熔体供应之间的关系仍然不确定。该项目使用了现有的CHIRP数据，这些数据是2013年AUV Sentry在大西洋中脊纬度16.5°N的14次潜水中获得的。研究目标是提供新的CHIRP处理方案，以便更快地处理CHIRP声纳数据，并利用现有数据定量确定沉积物厚度的变化，从而确定研究区域剥离断层滑动和火山活动的相对时间。这项研究为现有的数据集增加了重要的价值，这些数据集是在深海的一个难以接近的部分获得的，并将以经济有效的方式向科学界和公众提供一个开源软件工具。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The deepest parts of Earth's oceans are remote and difficult to explore. Thus, the geological, biological, and chemical processes taking place there remain poorly understood. Advances in autonomous underwater vehicle (AUV) technology in the past decade mean that we can now send these vehicles to the seabed in water depths of several miles where they collect data from just above the seafloor. AUVs are often equipped with a high-resolution compressed-high intensity pulse (CHIRP) sonar, which can capture centimeter-scale-resolution, cross-section images of the sediment that blankets the seafloor. These thicknesses can then be used as proxies for the length of time a feature has been exposed on the seafloor. Despite this potential, time constraints and a lack of an easily available sonar data processing scheme means that these CHIRP data are often under-utilized. This research develops a standard workflow and software for processing EdgeTech CHIRP sonar data, for use both at sea and on shore, using already existing AUV-acquired CHIRP surveys of sediment from a specific location on the Mid-Atlantic Ridge and other associated imaging data. Application of the processed data will be used to measure sediment thickness in an area where knowledge of this parameter advances our understanding of the interplay between the faulting and volcanism at mid-ocean ridge axes. Broader impacts of the research add value and capability to the existing US AUV fleet and advance our understanding of crustal formation at mid-ocean ridges. The methods and outcomes of the work will be incorporated into professional development workshops for in-service teachers in the highly diverse San Diego Unified School District, providing resources for lessons that can be widely used throughout the school system and support an early career investigator.In areas far from terrestrial sources, sediment thickness in deep sea marine environments is a rough proxy for the amount of time a feature has been exposed on the seabed. Thus, this provides a way to constrain the timing of geological events, such as volcanic eruptions and/or slip on faults. At young features, such as mid-ocean ridges axial valleys, sediment is typically only a few meters thick and so cannot be picked up by other shipboard geophysical/seismic imaging tools. These sediment thicknesses, at present, can only be imaged using near-bottom sonars such as those carried by AUVs. Use of these tools is particularly useful at slow-spreading mid-ocean ridges where the interplay between low-angle faults, know as detachments, and volcanism remains poorly understood. Although it is now clear that vast areas of seafloor are created under the influence of detachment faults, the relationships between detachments and magmatism and melt supply remain uncertain. This project uses already existing CHIRP data, acquired during fourteen dives of AUV Sentry at latitude 16.5°N on the Mid-Atlantic Ridge in 2013. Research goals are to provide new CHIRP processing protocols that can be used to more quickly process CHIRP sonar data and to use the existing data to quantitatively determine variations in sediment thickness and, thus, establish the relative timing of detachment fault slip and volcanism in the study area. The research adds significant value to an existing dataset that was acquired in an inaccessible part of the deep ocean and will deliver an open-source software tool to the scientific community and the public in a cost-effective way.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.