N242-095 TITLE: Directional Wave Spectra Sensing Module for Autonomous Underwater Vehicle Gliders

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Computing and Software; Integrated Sensing and Cyber; Trusted AI and Autonomy

OBJECTIVE: Develop and integrate a directional spectra sensor for ocean surface waves on low-power, long-duration autonomous underwater vehicle gliders.

DESCRIPTION: Autonomous underwater vehicle gliders are buoyancy-propelled, ocean-going robots that serve as platforms for a variety of environmental sensors. Gliders surface regularly to communicate with a base station via satellite communications. During this period, the glider floats at the ocean surface under the action of the surface waves. The goal of this SBIR topic is to develop a sensor to measure the directional wave spectra from low-powered, long-duration ocean gliders [Ref 1].

Measuring the strength, direction, and period of ocean surface waves is the primary component of sea state – an essential ocean variable. Measuring sea state is critically important for predicting ocean conditions that affect the safety of all maritime operations. Typically, directional wave spectra are measured from ocean buoys equipped with accelerometers. Recently, free-drifting floats [Ref 2] and autonomous surface vehicles [Ref 3] have been used to sense directional wave spectra using electromagnetic velocity sensors and Global Positioning System (GPS) velocity information. Measuring surface wave conditions has not been regularly achieved on ocean-going, autonomous gliders.

The Navy seeks development of a fully integrated, low-power, directional waves spectra sensor for ocean surface waves on ocean gliders. While all components – glider platforms, motion sensors (accelerometers, GPS, electromagnetic, etc.), and compression analysis software – are available in commercial, off-the-shelf components, integrated systems that allow for real-time sensing, onboard computation of directional spectra, and delivery of information via satellite communications are still in their infancy. Partnering with academic research groups utilizing autonomous gliders as sensor platforms will simplify integration efforts. The glider-based surface wave directional wave spectra should align with wave measurement standards outlined by the Coastal Data Information Program [Ref 4].

PHASE I: Identify hardware components that can meet the necessary motion sensing requirements. Develop a concept for onboard processing and data transfer of directional wave spectra [Ref 4]. 3.) Plan for integration of hardware and software components with glider platform, including transfer function for platform motion to wave action. Analyze the strengths and weaknesses of the proposed design. Prepare a Phase II plan that will include a design review.

PHASE II: Develop and test a prototype system. Perform an analysis of an integrated system, including in situ validation of directional wave spectra measurements. Report results. Perform multi-stage testing allowing for redesign between tests with initial tests in a surrogate ocean environment (e.g., lake or tank), interim tests in the ocean under controlled conditions (e.g., coastal bay), and final tests in the open ocean under environmental conditions. Both hardware and software systems should be developed and tested during Phase II. The final prototype should include a fully integrated sensing package capable of reporting directional wave spectra parameters via glider satellite communications. Analyze and report on the strengths and weaknesses of the final design based on results of the field tests.

PHASE III DUAL USE APPLICATIONS: The developed technology has use in the DoD’s operational glider fleet. The Naval Oceanographic Office (NAVOCEANO) utilizes numerous gliders within the Glider Lab and Glider Operations Center. Directional spectra of surface waves can be integrated into Navy models implemented by the Fleet Numerical Meteorology and Oceanography Center, improving forecast accuracy and improving safety of navigation and operations. Similarly, NOAA can utilize the wave monitoring capabilities to improve forecasts of wave conditions for commercial fishing operations and public safety.

REFERENCES:

1. Alvarez, A. "Assessment of sea wave spectra using a surfaced glider." Deep Sea Research Part I: Oceanographic Research Papers, 102, 2015, pp,135-143. https://doi.org/10.1016/j.dsr.2015.04.015
2. Hsu, J. "Observing Surface Wave Directional Spectra under Typhoon Megi (2010) Using Subsurface EM-APEX Floats." J. Atmos. Oceanic Technol., 38, 1949-1966, https://doi.org/10.1175/JTECH-D-20-0210.1
3. Thomson, J.; Girton, J. B.; Jha, R. and Trapani, A. "Measurements of Directional Wave Spectra and Wind Stress from a Wave Glider Autonomous Surface Vehicle. J. Atmos. Oceanic Technol., 35, 2018, pp. 347–363. https://doi.org/10.1175/JTECH-D-17-0091.1
4. Coastal Data Information Program (CDIP). https://cdip.ucsd.edu/m/documents/data_processing.html

KEYWORDS: Surface waves; autonomous glider; directional spectra

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