Collaborative Research: Continental Shelf Geodesy: Continued Development of a Low Cost Sea Floor Geodetic System Based on GPS

现有的海底大地测量技术（测量海底的微小运动）在精度和成本方面存在局限性。在浅层大陆架环境中尤其如此，在那里，海洋的盐度、温度和密度变化很大，给声波测距和海底压力技术带来了问题。该系统的潜在应用包括监测水下火山、海上油气田和俯冲带的浅海部分。测量俯冲带浅海区域的应变积累和释放过程尤为重要，因为它有可能提高我们对巨大俯冲带地震和海啸的理解，以及提高我们预测这些灾难性事件的能力。提出的设计是基于一个成功的意大利概念，将高精度GPS安装在半刚性结构上，并系泊在海底。该系统已经成功地在活火山侧翼的140米水深处进行了测试，但只获得了垂直分量的数据。意大利的设计已经进行了修改，以降低成本，并能够测量完整的三维位移矢量。最初的试验表明，简单的刚性梁设计适用于水深达40米的地方。一根钢梁通过锁扣固定在一个沉重的海底锚上，并通过一个近水面的浮子保持近乎垂直。浮标顶部的GPS测量瞬时位置，而倾斜和航向传感器允许校正浮标运动，使海底锚位置的每日估计精确到1-2厘米。这里提出的新研究旨在通过在浮标上添加带有方向传感器的电缆，开发并展示一种更深水的版本，适合水深达150米。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。

Existing technology for sea floor geodesy (measuring small motions of the sea floor) has limitations in terms precision and cost. This is especially true in the shallow continental shelf environment, where highly variable salinity, temperature and density of the ocean cause problems for acoustic ranging and sea floor pressure techniques. Potential applications of the proposed system include monitoring of underwater volcanoes, offshore oil and gas fields, and the shallow offshore portion of subduction zones. Measuring strain accumulation and release processes in the shallow offshore region of subduction zones is especially important because it has the potential to improve our understanding of giant subduction zone earthquakes and tsunamis, as well as improve our ability to forecast these catastrophic events.The proposed design is based on a successful Italian concept that uses high precision GPS mounted on a semi-rigid structure and moored to the sea floor. That system has been successfully tested up to 140 meters water depth on the flanks of an active volcano, but only acquired vertical component data. The Italian design has been modified to reduce costs and enable measurement of the full three-dimensional displacement vector. Initial tests have demonstrated that a simple rigid spar design is suitable for water depths up to 40 meters. A steel spar is attached by shackle to a heavy seafloor anchor and is kept near vertical by a near-surface float. GPS on top of the buoy measures instantaneous position, while tilt and heading sensors allow correction for buoy motion, enabling daily estimates of the position of the sea floor anchor precise to 1-2 cm. The new research proposed here aims to develop and demonstrate a deeper water version, suitable for water depths up to 150 meters, by adding a cable with orientation sensors to the buoy.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.