Collaborative Research: Novel Designs of GNSS-Acoustic Surveying for Low-Cost Seafloor Geodesy

About This Grant

Precise measurements of Earth’s surface motion and deformation are critical for understanding and mitigating natural hazards such as earthquakes, volcanic eruptions, and landslides. On land, the Global Navigation Satellite System (GNSS) and several other geodetic techniques have enabled high-precision, affordable, and continuous monitoring of surface deformation. In contrast, humans’ current ability to monitor the ocean floor – where many hazardous events originate – remains severely limited due to technical challenges and high costs. As a results, large portions of the solid Earth, particularly offshore regions prone to earthquakes, tsunamis, and submarine volcanic activities, remain unmonitored. This project addresses the gap by developing new, low-cost methods to measure seafloor motion over time. These methods reduce reliance on expensive seafloor instruments by employing innovative surveying strategies and alternative seafloor components. The approach has the potential to significantly lower the cost of seafloor geodesy and expand its spatial coverage. In addition to advancing scientific capabilities, the project provides hands-on training for students and early-career researchers, contributing to the development of a skilled geodetic workforce. Global Navigation Satellite System–Acoustic ranging (GNSS-A) is a major technique for seafloor geodesy. The conventional GNSS-A method requires at least three acoustic transponders per site, each costing tens of thousands of dollars, thereby limiting the number of deployable sites. These multi-transponder systems are also vulnerable to individual instrument failure because all transponders at each site need to function normally to form effective geodetic observations. In addition, a traditional GNSS-A site requires flat seafloor relief to mitigate errors associated with oceanic variability. This project aims to overcome these limitations by developing alternative GNSS-A configurations using only one transponder or a passive acoustic corner reflector per site, combined with symmetric survey designs using multiple semi-autonomous Wave Gliders. Five GNSS-A stations (four with transponders and one with an acoustic corner reflector) will be deployed at water depths between 85–1100 meters offshore Oregon and southern California. Additionally, one existing site deployed by the Near-Trench Community Geodetic Experiment will be utilized in this project. These sites will be surveyed multiple times over a three-year period to assess the repeatability of seafloor positioning. A Wave Glider-based winched ocean profiler will also be tested to improve sound speed modeling for improved GNSS-A data analysis. 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.