Unmanned Underwater Systems in Search and Rescue (SAR)

Unmanned Underwater Systems in Search and Rescue (SAR)

Malaysian Airlines flight MH370, a scheduled flight from Kuala Lumpur to Beijing, disappeared with very little trace  on March 8th, 2014. The search areas for the missing aircraft were determined based on final pings from the aircraft to a satellite. These areas focused the search in several bodies of water, including the Gulf of Thailand, South China Sea, and Southern Indian Ocean. The underwater search for the missing 777-200ER was focused off of the western coast of Australia and utilized several unmanned systems, including a Bluefin-21, an unmanned underwater vehicle (UUV) manufactured by Bluefin Robotics (BBC, 2014).

The Bluefin-21 is an autonomous underwater vehicle with a diameter of 21 inches and a length of 16.2 feet (General Dynamics, 2017). This 1,650 lb vessel is capable of a 25 hour endurance with a standard payload at a speed of 3 knots (General Dynamics, 2017). Onboard are several sensors, including an inertial measurement unit (IMU), global positioning system (GPS), Doppler Velocity Log (DVL), and a compass(General Dynamics, 2017). Unmanned underwater vehicles must be capable of operating autonomously without communication for long periods of time. For data gathering, the Bluefin-21 is commonly packaged with a EdgeTech 2200-M 120/410 kHz side scan sonar, EdgeTech DW-216 sub-bottom profiler, and a Reson 7125 400 kHz multibeam echosounder (General Dynamics, 2017).

Followup Questions

Sensors Specifically Designed For Maritime

Three of the four proprioceptive sensors aboard the Bluefin-21 are standard in all unmanned vehicles: the IMU, GPS, and compass. The proprioceptive sensor unique to USVs is the Doppler Velocity Log. A Doppler Velocity Log measures water current velocities at a range of depths. In a submersible vehicle this sensor is combined with other proprioceptive sensors to estimate the position of the vehicle in the body of water. The Bluefin-21 is outfitted with a Teledyne RDI Workhorse Navigator 300kHz DSV which provides measurements at 4 altitudes, heading, tilt, and temperature (Ashtead Technology, 2017).

Two of the three exteroceptive sensors used aboard the Bluefin-21 are sonic sensors which map out the sea floor. Both are made specifically for use on maritime vehicles. The third sensor, a turbidity meter, is used to measure the clarity of the water. Unlike unmanned ground and aerial vehicles, underwater vehicles do not use RADAR. RADAR sensors are not used due to the almost immediate absorption of microwaves by seawater, rendering the sensors useless. LIDAR sensors are occasionally used for undersea scanning but are cost prohibitive in comparison to sonic sensors. The sonic sensors aboard the Bluefin-21 are the EdgeTech 2200-M 120/410 kHz side scan sonar and the EdgeTech DW-216 sub-bottom profiler (General Dynamics, 2017). The turbidity meter is a Reson 7125 400 kHz multibeam echosounder (General Dynamics, 2017).

Modification for Maritime Search and Rescue

To make the Bluefin-21 more successful in deep sea maritime search and rescue operations, I would suggest that the vehicle be capable of an increased depth rating. The Bluefin-21 has a depth rating of 14,763 feet (General Dynamics, 2017). MH370 is estimated to be at a depth of 15,000 feet, however, the Indian Ocean possesses trenches that are much deeper. For example the Java Trench is 24,442 feet deep (Encyclopædia Britannica, 2017). The Wharton Basin, near the west coast of Australia and the presumed wreckage of MH370, is between 15,000 and 24,442 feet, far lower than the depth rating of the Bluefin-21.

UAS and Maritime Unmanned System cooperation

In the case of Malaysian Airlines flight 370, the first search vehicles used were manned aircraft. If properly equipped, the search teams could utilize unmanned aircraft which can be deployed quickly and in greater numbers than manned aircraft. Ideally, a network of unmanned aircraft could be deployed to scan areas with visible spectrum, RADAR, LIDAR, and infrared sensors, sending data back to teams on the ground. The data could be analyzed for any unexpected objects.

Unmanned Maritime System Advantages

Unmanned underwater systems have two distinct advantages over their manned counterparts. First is the size of the vessel. An unmanned submersible can be a fraction of the size of a manned submersible. The Bluefin-21 is only 21 inches wide. A small manned submersible is at least 6 feet in diameter. This is a dramatic increase in size, materials, and cost. The second distinct advantage that an unmanned submersible has over its manned counterpart is the ability to operate for days, weeks, or even months at a time. A manned vessel needs many life support systems such as waste management, water management, air management, and many types of storage for food, clothing, toiletries, etc.

References

BBC (2014, April 14). Missing flight MH370: Robotic submarine to begin search. British Broadcasting Company (BBC). Retrieved from http://www.bbc.com/news/world-asia-27017928

General Dynamics (2017). Bluefin-21 Autonomous Underwater Vehicle (AUV). Retrieved from General Dynamics Mission Systems' website on November 28, 2017 from https://gdmissionsystems.com/products/underwater-vehicles/bluefin-21-autonomous-underwater-vehicle

Ashtead Technology (2017). Teledyne RDI 300Khz Workhorse Navigator DVL Product Page. Retrieved from Ashtead Technology website on November 28, 2017 from http://www.ashtead-technology.com/rental-equipment/rdi-300khz-navigator/

Encyclopædia Britannica (2017, July 25). Indian Ocean. Retrieved from Encyclopædia Britannica website on November 28, 2017 from https://www.britannica.com/place/Indian-Ocean