Case Study of Sustainable Loop Current Monitoring Utilizing Solar-Powered Autonomous Surface Vehicles

Abstract

Abstract The Loop Current (LC) and Loop Current Eddies (LCEs) in the Gulf of Mexico (GoM) have significant implications for assets operating in the region, and ocean current data at and below the surface are critical to understanding and forecasting these phenomena. The advent of uncrewed systems enables new methods for collecting these data in a sustainable manner while minimizing the Health, Safety, Security and Environment (HSSE) risk associated with traditional vessels. A study was conducted to better understand both how commercially available Autonomous Surface Vehicle (ASVs) can be used to collect these data, and how the data products compare to traditional industry sources. A 4.8m solar powered ASV from SeaTrac Systems was deployed in the Gulf of Mexico for 39 consecutive days configured with an Acoustic Doppler Current Profiler (ADCP), wind and wave sensor onboard. The LC and LCE were mapped utilizing Sea Surface Height (SSH), Sea Surface Temperature (SST), the Copernicus Mercator model for geostrophic current velocities, and real time measurements from the ADCP onboard the ASV. Survey patterns were formulated to maximize spatial coverage and cover ground as efficiently as possible with respect to power consumption while collecting useful data about the LC and LCE. Transiting over 2900 km under supervision of a remote piloting team, the ASV logged operational data, including propulsion power and solar generation, to analyze, quantify, and compare different piloting strategies. The piloting plan focused on first collecting data in the vicinity of several assets (buoys and rig mounted sensors) that could be used to compare and assess the quality of the data in a range of sea states and environmental conditions. The data collected show a strong correlation between those from the ASV, and those from the buoys and rig mounted assets across all the conditions tested. The second objective was to conceptualize and test different strategies for data collection and analyze them to understand their benefits and limitations. A range of patterns and piloting strategies were tested, some intended to mimic the "manned/status quo", others intended to leverage the benefits of solar powered, uncrewed platforms. The study found that long duration operations with this type of sustainable platform are viable in the LC/LCE environment, and that behaviors with different power consumption requirements can be employed to achieve survey objectives while balancing energy usage with solar generation in a wide range of conditions. A third opportunistic objective was to evaluate the utility of ASVs for asset inspections after significant weather events. No major storms occurred during the trial, but the ASV demonstrated the ability to capture and send back images of several representative assets. This project concludes that ASVs present a viable option as a lower risk, sustainable tool for ADCP surveys in the GoM around the LC and LCEs, but operations must be adjusted for the limitations and capabilities of the platform to maximize value to stakeholders. Further work is needed to expand from a single ASV concept to multiples intelligently working together and collecting data that more comprehensively describe features of interest in ways not possible or practical with traditional approaches.