Distributed and controlled sensing of submesoscale, internal wave, and mixed layer flows and their impacts on acoustic and non-acoustic vulnerabilities
Abstract
We propose to improve the state-of-the-art ocean applications of fiber optic Distributed Sensing by developing techniques to enhance precision, decrease energy burden, and to acquire simultaneous distributed temperature (DTS) and distribute strain (DAS) measurements on fiber optic cables of indeterminate length. These distributed measurements will be augmented by a relatively incrementaldesign change to our time-proven Wirewalker wave-powered vehicle to allow autonomous profiling control for tracking depth and isopycnal surfaces. While each improved system will individually augment current and planned ONR efforts, the co-development of these technologies allows for their integration. Here we plan to combine the technologies by building an surface mooring with integrated optical fibers. DTS/DAS measurement will be acquired continuously in depth and time along the mooring wire via an interrogator in the surface buoy, while a Wirewalker, affixed to the same wire, will provide user or autonomous-selected variable profiling. This #peanut-butter and jelly# synergy combines the strengths of both platforms while minimizing their weaknesses: the relatively slow Wirewalkerprovides multi-parameter profiles with oceanographic precision and high vertical resolution on time scales of tens on minutes, while the DTS provides temperature measurements at all depths every few seconds. Fiber Optic DTS improvements: DTS is a revolutionary sensing technology pioneered for oceanographic measurements by our group. DTS has been proven in fixed mounted deployments across large temperature gradient regimes. Future in the deep-sea, the mixed layer, and towed applications will challenge the precision of current commercially available DTS systems. Moreover, #navigation# of a fiber optic cable to earth or fluid referenced coordinate systems requires very detailed information regarding the cable shape, particularly in towed scenarios. Modern distributed acoustic sensing (also known as strain sensing) is capable of determining cable catenary as a function of length for the validation of towed cable models. Our proposed development of an improved DTS/DAS combination system could be used in a fixed-in-place seabed mode, deployed from moored surface buoys, and could be directly and easily added to our group#s shipboard profiling systems, turning the profiling or tow cable itself into a sensor. In a moored, autonomous mode, a vertical DTS/DAS fiber optic cable has the potential to provideeffectively continuous time and vertical temperature measurement over ranges larger than the average ocean depth (i.e. >3km). The Wirewalker improvements: ocean-wave-powered profiling system is a proven platform used several past and present ONR DRIs. The current mechanically actuated version will be augmented by an incremental change to include user or autonomous actuation. The design isbased on a successful actuator and controller development for our towed Phased Array Doppler Sonar fish and our rapid profiling Fast-CTD fish. Although an incremental design change to the overall Wirewalker system, this will be a major enhancement because it willallow parking or hovering at user or autonomously specified isobar or isopycnal or isotachs or isolume, etc., to collect time-series or to employ slow response sensors like those common for biogeochemical measurements. When deployed on a profiling cable with an integrated optical fiber, collecting DTS/DAS measurements simultaneously ameliorates the #cost# of parking/hovering (i.e. being a fixed depth).This abstract is publicly releasable.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 06, 2023
- Source ID
- N000142312233
Entities
People
- Andrew J. Lucas
Organizations
- Office of Naval Research
- United States Navy
- University of California, San Diego