GHOST: Instrument Data Delivery from Sub-Surface Moorings

Transmitting instrument data files via satellite directly from anchored sub-surface moorings has just become a reality. The ability to capture data prior to mooring recovery allows traditional subsea remote sensing installations to become near real-time observation systems.

GHOST, which stands for Global Hidden Ocean Satellite Telemetry, is a newly developed data delivery tool designed to advance the capability of sub-surface moorings by providing a means to automatically and periodically extend a satellite antenna above the ocean surface to transmit instrument data and then lower itself back to a hidden and safe depth below. This tool is easily adaptable to existing moored data collection applications and new monitoring applications previously thought not possible.

BENEFITS TO EARLY DATA CAPTURE

Near real-time observation capability is only one benefit of many that early project data reporting provides. Knowing that valuable data would not be entirely lost if an instrument fails prematurely or the mooring recovery operation is not successful provides added assurance of data recovery. Unanticipated events caused by water ingress, internal battery leakage, or housing impact damage during recovery operations can result in complete data loss. In some circumstances the entire mooring may not be recoverable due to equipment failure, difficult sea conditions or the mooring is missing. Data files can be captured prior to the time of instrument failure and transmitted safely upon the next programmed transmission cycle. In the event a mooring prematurely separates from its anchor with no ability to send a vessel to the site, the instrument data will automatically be transmitted when GHOST reaches the ocean surface and obtains a satellite link. Another benefit to collecting data remotely includes reducing ship time for remote sites that require frequent visits to physically link instruments to download data.

R&D EVOLUTION

Real-time transmission of underwater oceanographic instrument data using moored surface buoys is common practice with several standardized methods used to achieve acceptable survival life. Typical methods include electro-mechanical cables with bend relief devices for protecting the integrity of cables or the simpler approach of inductively coupling instruments using inductive modems and jacketed wire rope. Despite these successes, designing for survival against surface buoy motion under harsh environmental conditions can still lead to premature mooring failure and vandalism to surface buoys remains a problem in many regions around the globe.

GHOST evolved from an earlier design effort by Mooring Systems, Inc. named (ARROW), which began back in 2011. Arrow was an innovative Tsunami detection system aimed at deployment in areas prone to surface buoy vandalism. This system included the use of expendable pop-up buoys to transmit Tsunami alert data and thus eliminate the need for a moored surface buoy altogether. Unfortunately, a limitation in the number of pop-up buoys per system was insufficient in meeting the number of possible alert events that could occur within one year along with the number of routine status reports desired (also via pop-up buoys) to confirm the system is operational and system ready.

The development of GHOST was a self-funded effort to not only satisfy the continued and very important need for a Tsunami detection system not prone to vandalism but to expand the technical capability of sub-surface moorings by providing near real-time data capture for many other moored instrument applications.

DESIGN HURDLES

Tackling this problem included applying fundamental oceanic mooring design principles, adapting a data signal carrying method, and designing a motorized self-powered vessel programmed to automatically travel up and down through the water column.

Our extensive experience with the use of jacketed wire rope as a component to carry inductive data signals on moorings was an easy choice for the system. Mechanical challenges included the requirement for a seawater grounded signal loop through the jacketed wire rope that also rotated on a drum. The use of our standard Hammerhead wire rope terminations provided a robust and proven method to secure and link the system inductively to the top of any sub-surface mooring buoy. A jumper from the termination would provide a connection point for the instrument’s inductive signal to link to. The jumper would also attach to another Hammerhead termination on the mooring to continue the inductive link downward along the mooring to instruments mounted further below.

Developing a motorized vessel required balancing its power system payload weight and size with the required volume of buoyancy needed to meet acceptable mooring performance. Designing for good mooring performance requires sufficient buoyancy and the use of low drag shapes to meet anticipated current velocities for typical deployment sites. With these fundamental goals we were able to package the components needed for a self-powered payout and retrieval system that met a minimum power consumption amount to provide multiple cycles up and down through the water column for its intended deployment period. Our design team included a highly experienced controls engineer with many years of experience in both system automation and underwater inductive modem use on buoy observation systems. The automation built into the system provided the motor control linked with the instrument download and satellite telemetry to produce a programable system to carry out the desired missions.

GHOST IN THE FIELD

The result of this engineering effort produced a commercially available tool for aiding in ocean research, observation, and Tsunami detection.

GHOST easily attaches to the top of any sub-surface mooring’s upper most buoy with the use of standard shackles and rings. The Hammerhead wire rope termination provides the necessary isolation from the mooring hardware and makes the inductive-ready link.

GHOST consists of two primary components, the motorized vessel referred to as TRANSPORTER, and a tethered TRANSMITTER BUOY. Transporter is self-powered and travels up and down through the water column to transport the transmitter buoy to the ocean surface multiple times throughout its pre-defined mission. The transmitter buoy is connected to Transporter via a fixed length of electro-mechanical cable and houses the satellite antenna. Only the transmitter buoy will breach the ocean surface spending less than 5 minutes to transmit collected instrument data files. Transporter will remain just below the sea surface during the transmission then retract to a safe and hidden park depth.

The brain of the system is an intelligent controller that requires no user interaction during deployment operations. The controller is pre-programmed to collect data from multiple instruments installed on the sub-surface mooring and transport the antenna to the surface for the satellite transmission at pre-defined time intervals. Smart features built into the system provide assurance the system will never exceed its pre-programmed depth for the selected mission. Proprietary components and automated control systems have been uniquely designed into the pay-out and retrieval system to provide a robust and seawater resistant design. Sea trials were conducted to test all functions of the system including the failsafe conditions designed for safe and reliable operation. Recommended deployment and recovery methods of the system components were determined based on actual field use.

This new TAUV (tethered AUV) product entry opens new possibilities in ocean observation systems. The ability to remotely capture subsea instrument data files and deliver those files to a host computer from any water depth in any ocean and virtually without ever being visible is a game changer for ocean science, marine conservation, Tsunami detection, and security.

Our focus on making data recovery a priority goes hand in hand with our track record in building robust moorings designed to meet a required survival life. This product is patent pending. For more information, visit www.mooringsystems.com

This article was originally featured in ON&T February 2021. Click here to read more.