Date of Award
2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Ocean Engineering
Department
Ocean Engineering
First Advisor
Brennan Phillips
Abstract
Over the last two decades, fiber optic distributed temperature sensing (DTS) has emerged as a transformative technology capable of providing unprecedented spatiotemporal resolution observations of temperature in a broad range of environmental sensing, industrial, and civil engineering monitoring applications. DTS uses a single interrogator unit to measure temperature continuously along an optical fiber, effectively turning the fiber into the equivalent of an array of temperature probes that can be interrogated synoptically. Modern commercially-available DTS systems are capable of continuous sensing with sampling frequencies up 5 sec, spatial resolution of 0.25 m, and temperature precision up to 0.01 °C) observations, on optical fibers up to >10 km in length. To date, applications of DTS technology for oceanographic research have been limited to nearshore and water column environments using shore- and ship-based interrogators. While these are suitable methods to use at many study sites, there are several unique ocean environments, such as hydrothermal vent fields, that could significantly benefit from the capabilities of DTS that are impossible to observe using topside interrogators. These applications highlight the need for a subsea in situ DTS solution. This study details the development of a deep-sea DTS observatory and data processing workflow, along with the results of multiple field deployments in coastal and deep-sea environments.
A comprehensive review of previous DTS environmental monitoring studies and commercially available DTS products was performed along with extensive preliminary lab and field testing using a Silixa XT DTS. Preliminary field experiments included the installation of a coastal observatory at the Castle Hill Lighthouse, RI, and ship-based water column profiling experiments on the Rhode Island continental shelf and off the coast of Bermuda. These results reflect the current state of DTS field methodologies and provided crucial experiential knowledge used to advise the development and deployment of a deep-sea in situ DTS observatory.
In the development of a deep-sea DTS observatory, a Silixa XT-DTS system was modified and converted to fit into a custom-designed 6000-m rated pressure housing. Customized stainless-steel reels loaded with ~500m of sensing fiber and integrated optical slip-rings were constructed, and battery systems were developed. The platform was first deployed at the ABE vent field on the Eastern Lau Spreading Center (ELSC) in 2022 for 4 days where a small transect of fiber was unspooled onto the seafloor encountering an active source hydrothermal discharge. Based on the success and challenges of this deployment, the observatory and deployment methods were further refined including upgrades such as the development of a new battery system, custom deck testing and deployment-preparation equipment, and the addition of auxiliary current and temperature sensors and visual and bathymetric surveys. This enhanced DTS observatory was then deployed in a vent field scale, double-transect configuration at the Iguanas vent field on the Western Galapagos Spreading Center (WGSC) in 2023 for 7 days.
A specialized MATLAB-based software pipeline was developed to handle, analyze, and visualize the complex high-resolution datasets produced by deep-sea DTS deployments. The software incorporates calibration routines, spectral analysis tools, and visualization methods tailored to DTS data, facilitating comprehensive assessments of temperature variability influenced by oceanic tides, seafloor currents, and earth tide-induced crustal deformation. Spatial trends in temperature variability observed on the ELSC deployment suggest tidally induced currents play a role in the semi-diurnal temperature variability at this site, however, due to short deployment time periods, comparative spectral analyses at these periodicities in both the ELSC and WGSC deployments are inconclusive. The success of these deployments demonstrates the potential of DTS at hydrothermal vent fields and future plans are presented for a long time-series deployment on the scale of 1 year at the ONC NEPTUNE cabled observatory in 2025.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Becker, Johann Sebastian, "DEVELOPMENT AND DEPLOYMENT OF IN SITU FIBER OPTIC DISTRIBUTED TEMPERATURE SENSING SYSTEMS AND DATA PROCESSING WORKFLOWS FOR OCEANOGRAPHIC OBSERVATORIES IN COASTAL AND DEEP-SEA ENVIRONMENTS" (2025). Open Access Dissertations. Paper 4440.
https://digitalcommons.uri.edu/oa_diss/4440