Barbara Fletcher

The Nereus hybrid underwater robotic vehicle for global ocean science operations to 11,000m depth

This paper reports an overview of the new Nereus hybrid underwater vehicle and summarizes the vehicles performance during its first sea trials in November 2007. Nereus is a novel operational underwater vehicle designed to perform scientific survey and sampling to the full depth of the ocean of 11,000 meters - almost twice the depth of any present-day operational vehicle. Nereus operates in two different modes. For broad area survey, the vehicle can operate untethered as an autonomous underwater vehicle (AUV) capable of exploring and mapping the sea floor with sonars and cameras. For close up imaging and sampling, Nereus can be converted at sea to operate as a tethered remotely operated vehicle (ROV). This paper reports the overall vehicle design and design elements including ceramic pressure housings and flotation spheres; manipulator and sampling system; light fiber optic tether; lighting and imaging; power and propulsion; navigation; vehicle dynamics and control; and acoustic communications.

Chemical plume mapping with an autonomous underwater vehicle

A REMUS (Remote Environmental Measuring UnitS) autonomous undersea vehicle (AUV) is being used for chemical plume mapping as part of the Office of Naval Research (ONR) Chemical Sensing in the Marine Environment (CSME) program. Bathymetric, current, temperature and fluorometric data are collected while the vehicle performs a ladder type search across and downstream of a dye source. These data are used to validate and refine an analytical plume model. Operational experiences and data collected will be presented from operations at San Clemente Island, California and Duck, North Carolina.

Proof of concept demonstration of the Hybrid Remotely Operated Vehicle (HROV) light fiber tether system

The Hybrid Remotely Operated Vehicle (HROV) Nereus, developed by the Woods Hole Oceanographic Institution (WHOI) with the support of the Space and Naval Warfare Systems Center San Diego (SSC San Diego) and the Johns Hopkins University, is intended to provide a new level of access for deep oceanographic research to a maximum depth of 11,000 meters. Nereus operates in two different modes. The vehicle can operate untethered as an autonomous underwater vehicle (AUV) for broad area survey, capable of exploring and mapping the seafloor with sonars, cameras, and other on-board sensors. Nereus can be converted at sea to become a remotely operated vehicle (ROV) to enable close up imaging and sampling. The ROV configuration incorporates a lightweight fiber optic tether to the surface for high bandwidth real-time video and data telemetry to the surface to enable high-quality teleoperation, additional cameras and lights, a manipulator arm, and sampling gear. Development of the fiber tether system was supported by both simulation and extensive field testing over a three year period. These tests demonstrated that an unprotected optical fiber could survive in the water column for greater than 24 hours and be effectively used as a high bandwidth data link by a remotely-operated, self-powered vehicle. Based on the data from the fiber trials, a robust tether deployment system was designed. The tether deployment system was integrated with the vehicle and demonstrated during field trials in November 2007.

Field Tests of the Hybrid Remotely Operated Vehicle (HROV) Light Fiber Optic Tether

The Hybrid Remotely Operated Vehicle (HROV), being designed and built by Woods Hole Oceanographic Institution (WHOI) with the support of the Space and Naval Warfare Systems Center San Diego (SSC San Diego), will provide a new level of accessibility for deep ocean research. HROV will be primarily an autonomous vehicle but will be reconfigurable to a teleoperated system by the installation of a fiber optic data link and a manipulator based work system. Development of the fiber optic link has been supported by both simulation and a series of field tests over the past 3 years. The November 2004 tests consisted of deploying two different types of fiber optic cable from an Oceanographic elevator deployed from a ship to 2000 m depth. Data collected from this test demonstrated the feasibility of using both the Fiber Optic Microcable (FOMC) and plain buffered optical fiber as a tether for the HROV. The December 2005 tests demonstrated the utility of the buffered optical fiber operating on an underwater vehicle using the WHOI ABE vehicle as a substitute for the future HROV. Five dives were made to 2000 m with real-time communication from the vehicle to the surface via the fiber. The May 2006 tests focused on the employment of a cable depressor and deployment system. Using a deep elevator as a substitute for HROV, the fiber was deployed from both the depressor and the elevator to a depth of 4200 m. Over the course of 4 deployments, over 16 km of fiber was deployed, operating for a total of 33 hours, demonstrating the feasibility of the planned approach

High frequency side scan sonar for target reacquisition and identification

The increasing use of small unmanned underwater vehicles (UUVs) for scientific, military and security applications has led to the development of new sensor technologies. Key among these has been the development of small, light, cost-effective side scan sonar systems, enabling small vehicles such as the REMUS and CETUS II to perform a variety of survey-type missions. New developments in side scan technology are increasing the capabilities of these systems, going beyond the simple detection of targets. Use of high frequencies such as 1.2 and 2.4 MHz can provide a sufficient degree of resolution for the recognition and identification of targets. The performance of these sonar systems will be discussed, as well as factors affecting performance such as speed, altitude, depression angle, and vehicle system interference.

Characterizing the critical parameters for docking unmanned underwater vehicles

Docking an autonomous underwater vehicle (AUV) is a critical part of many current and envisioned Navy, commercial, and scientific missions. Many missions require an AUV to dock with a subsea node that is not restrained through attachment to the seafloor or to a surface platform significantly larger than the system that is docking into it. Space and Naval Warfare Systems Center Pacific (SSC Pacific) recently performed a series of tests to characterize the docking process of an autonomous underwater vehicle (AUV) with a suspended dock. Two methods of docking were performed: a “soft” optical dock where the vehicle tracked and followed a suspended light emitting diode (LED) beacon and a “hard” physical dock where the vehicle entered a docking structure. This docking testing will provide design support information for future undersea systems. A REMUS 600 with a hover-capable thruster package was the base test platform. It was outfitted with a directional acoustic transducer (DAT) for acoustic AUV-Dock-relative navigation and an optical quadrant detector for terminal approach and homing. A basic dock structure was constructed of PVC pipe, and instrumented with both acoustic and optical homing devices. Testing was performed at the SSC Pacific Transducer Evaluation Center (TRANSDEC) test facility. Key docking parameters evaluated during the testing included sensor update rates, vehicle kinematics, and dock inertial characteristics. SSC Pacific performed over 217 trials, with 105 successful hard and soft docks. There were 30 successful docks in 31 trials in the final hard dock series.