Introduction
Unmanned vehicles perform a variety of tasks in every operational
domain: air, space, ground, surface of the water and on the bottom of the sea.
Unmanned underwater vehicles (UUVs) will be the focus of this paper. The underwater
environment is a challenging domain of operation due to high pressure, strong
currents, lack of light, extreme temperatures, water salinity, and other
factors. These issues can affect underwater communications, navigation and play
a roll in vehicle design, and sensors used on the underwater vehicles. In
recent years, the use of UUVs in search and rescue operations has significantly
increased. UUVs carry out such complicated and dangerous tasks as maritime patrol,
mine detection, and searching for missing aircraft and vessels. This paper will
focus on Bluefin-21 autonomous underwater vehicle (AUV), developed by Bluefin
Robotics. This particular AUV was used in 2014 in search efforts for Malaysia
Flight MH370 in the Indian Ocean. It scouted over 850 sq. km. of the ocean
floor in an effort to locate the missing
aircraft (Tokkecar, 2014).
The Bluefin AUV is suited for complicated search and rescue missions due to its
extensive sensor payload and tit’s ability to operate down to a depth of 1500 meters
at speeds of 2 to 4.5 knots. Its long endurance capability of 20 hours at sea
makes it a perfect search vehicle. Bluefin-21 follows a preprogrammed
“lawnmover” pattern to scan for debris on the sea floor. Figure 1 depicts the
Bluefin-21 being recovered onto the vessel with the crane.
Figure 1. Bluefin-21 Adapted from “Bluefin-21” by Bluefin
Robotics. Retrieved from
http://www.bluefinrobotics.com/vehicles-batteries-and-services/bluefin-21/ Copyright by
the Bluefin Robotics.
Bluefin-21 AUB sensors
The Bluefin-21 features an extensive sensor suit. The exteroseptive
sensors are sensors which are responsible for providing information about
vehicle’s environment and its position relative to other objects, and
environment features. The Bluefin-21 is equipped with the variety of
exteroseptive sensor which include:
- EdgeTech DW-216 sub-bottom profiler, which is ideal for
identifying and characterizing layers of sediment or rock under the seafloor
and other relevant features on the seabed (Kongsberg, n.d.).
- Inertial navigation
system, which is essential sensor for vehicles navigation underwater.
- Ultra-short baseline
system
- Side-scan sonar system EdgeTech 2200-M 120/410 kHz or optional
EdgeTech 230/850 kHz can be also installed improving focusing capability.
EdgeTech transmits a signal which creates a high-resolution 3D map of the
seabed, helping identify man-made objects, such as aircraft, which often have
right angle and sharp outlines.
The Bluefin-21 is equipped with GPS system. Due to degraded
communication and navigation signal
propagation though water, the UAV have to ascend every 30 minute to
acquire GPS signal and realign its position, resulting in about 50-100 m of
navigational error (Autonomus
Undersea Vehicles Application Center [AUVAC], n.d.). The Bluefin-21 is also
equipped with a digital camera as an optical payload. Some of the optional
payloads include sensors which measure chemical tracer concentrations or
biological contents in the water, such as algae, oil or hydrothermal vent fluid
(AUVAC, n.d.).
Proprioceptive sensors are responsible for monitoring
self-maintenance and controlling internal status of the vehicle. These sensors
include potentiometers for control surface positioning and pressure sensors for
monitoring vehicle’s depth. Linear velocities determined with a Doppler
Velocity Log (DVL). Angular rates, pitch and roll attitude is measures by IMU
sensor.
Sensors which are responsible of monitoring vehicles state to
maintain safe operations include: fault and leak detection sensors, drop weight
acoustic tracking transponder, strobe, RDF and Iridium. All of these sensors
are independently powered proving extra redundancy (Bluefin Robotics, n.d.).
The Bluefin-21 features the Mission Oriented Operating Suite
(MOOS) and the Interval programming IvHelm. This system coordinates and
programs autonomous behaviors of AUV, by controlling depth, speed, and heading
based on the sensor data and required vehicle behavior (AUVAC, n.d.). Figure 2 depicts
Buefin-21 Bluefin-12 AUV with a Buried Object Scanning Sonar (BOSS) integrated
in its wings.
Figure 2. Bluefin-21 with BOSS sonar.
Adapted from Adapted
from “Bluefin-21” by Bluefin Robotics. Retrieved from
http://www.bluefinrobotics.com/vehicles-batteries-and-services/bluefin-21/ Copyright by
the Bluefin Robotics.
What one modification would you make to the existing
system to make it more successful in maritime search and rescue operations?
Current design and sensor suit of Bluefin-21 AUV allows it to be a
perfectly suited for search and rescue operations. However, there is always a
room for improvement. Since time is a critical factor in the search and rescue
missions, modification of the vehicles propulsion system to allow for faster
area scanning would be beneficial. Another addition may be installation of
flashlight to allow take images in the areas where natural light is restricted.
Modifying the AUV launch system to allow it to be delivered using manned
helicopters or unmanned hover vehicles instead of slow-moving ships may be
helpful in time critical missions.
Since underwater communications and navigation is restricted due
to physical characteristics of the water and signal propagation, addition of
the gateway buoy would be beneficial. The gateway buoy, similar to one
developed by Kongsberg and used for Remus AUVs can be used in remote AUV
tracking, communication, and navigation. Gateway buoys uses standard alkaline
battery and saves power by automatically going into “sleep” mode during stages
of inactivity. Triangulation techniques can be used to aid in AUV location
using multiple buoys deployed in the known positions. Buoys may also be
equipped with GPS receiver and Iridum Satellite Modem (Kongsberg, n.d.)
How can the maritime system
be used in conjunction with UAS to enhance its effectiveness?
Collaboration between different types of unmanned vehicles in
search and rescue operations can have positive effect on the overall success of
the mission. Use of the unmanned aerial vehicle (UAV) in conjunction with
Bluefin-21 AUV could be beneficial. For example, the UAV payload such as
cameras and infrared radars may help locate and identify debris from the a crashed
aircraft or vessel and help focus the search on a particular region of
interest. The UAV can also provide a relay link for AUV communications with the
control station based on the ship or shore. The UAV also may deliver the UUV to
the search site much faster than the sea vessel, shortening the time for
delivery and launch and allowing the UUV to begin the search efforts faster in
a time critical situations. For example, it is important to detect emergency
locator transmitter signals and black box pinger signals in timely manner due
to its limited battery life.
What advantages do unmanned
maritime systems have over their manned counterparts? What sensor suites are
more effective on unmanned systems?
UUVs can carry out dangerous, dull, and dirty tasks in the
unforgiving environment of the ocean. By using the UUVs instead of manned
submarines, physical risk to the crew is removed. The ability of UUV to stay
underwater for extended periods of time without necessity for decompression is
another advantage of UUVs. Small size of UUV is also an advantage, since it can
go into confined spaces, inaccessible for large manned submarines.
One example of a sensor suite that would be more effective on a
UUV is the mine countermeasure sensors. This kind of dangerous mission is a
perfect task for an unmanned vehicle. For example, Bluefin12 Buried Mine
Identification (BMI) System can be used in search of buried mines. This system
consists of the bottom looking sonar, a Real-time Tracking Gradiometer (RTG),
and an Electro-Optic Imager (EOI) (Sulzberg, Bono, Manley, &
Clem, n.d.).
Sea trials of mine countermeasures using the Bluefin-21 were
conducted in 2008. The mission provided important data that proved that successful
sensor fusion aboard an UUV was possible. Researches used the RTG and the EOI
sensors in sea trials of the Bluefin-12 to evaluate, optimize, and demonstrate its
mine detection capability.
UUVs have many applications in a variety of missions and has
proven that unmanned systems can successful perform challenging tasks in the
dangerous and unforgiving underwater environments. This is accomplished with no
risk to the human operator, UUVs can perform successful long endurance, deep
ocean missions ranging from search and rescue, mine countermeasures,
environmental research and patrol and reconnaissance.
References
Excellent blog and posts Elena!
ReplyDelete-Prof Houston