Unmanned System Maritime Search and Rescue

In April 2016, the National Transportation Safety Board announced that the cargo ship El Faro’s voyage data recorder was located at the site where the vessel sunk after the ill-fated voyage during a hurricane last year.  The research vessel Atlantis, operated by Woods Hole Institute found the recorder using Sentry, an autonomous underwater vehicle that has an extensive sensor suite depending on the application.  Along with the other remote vehicles onboard Atlantis, they were able to find the object about the size of a basketball in almost three miles underwater.  NSTB Chairman Christopher Hart stated that it would not have been possible to find it without the help of the institutions and agencies involved in the search and the equipment provided (NSTB locates Sunken Cargo Ship, April 2016). 

The autonomous vehicle Sentry was developed with funding from the National Science Foundation, and designed and built by Woods Hole Institute.  The vehicle is operated the National Deep Submergence Facility (NDSF), funded by several US agencies.  The NDSF operates, maintains and coordinates the use of these deep ocean research vehicles (NSTB locates Sunken Cargo Ship, April 2016).

Based on the finding provided by Sentry, the NSTB announced on June 6^th, that USNS APACHE with the remote vehicle CURV-21 will be displaced in July to commence recover efforts of the recorder (NSTB to Launch Mission, June 2016). APACHE and CURV-21 were initially used last November to locate the sunken ship.  CURV-21 is a tethered remote operated vehicle with two 7-function manipulators and tool packages, which will be used to retrieve the recorder (CURV 21, n.d.). 

Sensor Systems

Sentry is a unique remote underwater vehicle capable of operating down to 6,000 meters, fully autonomously.   It is designed for quick maneuverability, and shaped to allow for faster ascents and descents. It carries an array of exteroceptive sensors to produce bathometric, side-scan, sub-bottom, and magnetic maps.  It has an acoustic navigational system that performs as a proprioceptive sensor.  The navigational system uses a Doppler velocity log and an inertial navigation, assisted by an acoustic navigation system. This acoustic navigational system also has proprioceptive attitude sensors to determine the pitch, roll and heading via a vertical reference unit (VRU) and gyrocompass. All these sensors were designed for the maritime environment (Sentry, n.d.; USBL Overview, n.d.).

Modification to the existing system

Sentry is currently used as a search platform.  Woods Hole Institute operates other manned and unmanned systems to complement Sentry when a full search and rescue operation is performed.  It also collaborates with the US Navy, NOAA and other agencies to use their unmanned platforms as required by the mission.  Sentry currently does not have any manipulators.  This is the reason the CURV 21 is going to be used to retrieve the recorder.  If Sentry had the capability to use manipulators, it could have retrieved the recorder when it initially found it. Now another effort must be done to retrieve the recorder. 

UAS use to complement the existing system

            In the cases where Sentry is used for deep dive searches, the use of UAS would have minimal value.  However, the use of UAS for the initial search and rescue operations would be beneficial as an additional search platform or as a communications relay for other search platforms.  UAS with maritime or synthetic aperture radars and electro-optic/infrared camera system would be invaluable to initially search a maritime area of interest.  It could cover magnitudes more amount of area than ships.  Operating sensors at higher heights and higher velocities, the aerial system will provide greater coverage and more frequent revisit rates. 

Advantages of unmanned maritime systems

            Sentry has significant advantages over manned systems since it can operate autonomously in a very harsh environment. The hull shape allows Sentry to get on station quickly, and can operate at great depths for long periods of time.  The ability to be autonomous provides the search and rescue team greater flexibility than a tethered manned or unmanned system.  They can do missions with Sentry in more hazardous areas and at a faster pace than with other systems in their inventory. 

            In the case of Sentry, it can cover an ocean floor effectively to find objects with the array of sonars and cameras.  At the same time, it is a small footprint. Therefore, it can operate effectively at a site, such as a shipwreck without disturbing the environment.  A manned tethered system that can carry a similar sensor array would not be able to explore the site as effectively because it would be difficult to maneuver the vehicle in the tight environment.  With visibility being so poor at great depths, a manned system may not be able to take the photographs or other sensor measurements as can the autonomous Sentry. 

References

NTSB Locates Sunken Cargo Ship's Voyage Data Recorder. (2016, April 26). Retrieved June 06, 2016, from http://www.ntsb.gov/news/press-releases/Pages/PR20160426b.aspx

NTSB to Launch Mission to Recover Voyage Data Recorder. (2016, June 6). Retrieved June 06, 2016, from http://www.ntsb.gov/news/press-releases/Pages/PR20160606.aspx

CURV 21. (n.d.). Retrieved June 06, 2016, from http://www.supsalv.org/00c2_curv21Rov.asp?destPage=00c2

USBL Overview. (n.d.). Retrieved June 06, 2016, from http://www.sonardyne.com/products/positioning/usbl-all-systems.html

Sentry. (n.d.). Retrieved June 06, 2016, from http://www.whoi.edu/main/sentry