Unmanned Underwater Vehicles in Search and Rescue (UNSY 605, 2.4)

          Search and Rescue (SAR) is a challenging mission that broadly covers locating and recovering distressed persons in all environments. Unmanned maritime systems currently have the potential to multiply the searching, communications, and networking capabilities of the rescue force. The highly dynamic nature of the actual rescue phase, especially in rough seas, urban/complex terrain, or inclement weather is beyond the capabilities of current or forecasted unmanned systems, so this research project will focus on a platform that will complement the search phase and support the rescue.

Bluefin-21 and the Search for Malaysian Airlines Flight MH370

          In April of 2014 a Bluefin-21 Autonomous Underwater Vehicle (AUV) was employed in a city-sized area in the Indian Ocean which potentially had the wreckage of MH370, and Boeing 777 with 239 people on board (Kaye, 2014). Built by Bluefin Robotics, the torpedo-sized AUV has a depth rating of 4,500m and endurance of 25 hours, making it ideal for wide area searches (Bluefin 2015). Another strength of Bluefin 21 is the field-replaceable payload sections.

Proprioceptive Sensors

• Inertial Navigation System (INS): The Bluefin’s INS drifts less than 0.1% of distance traveled per hour, which is critical when navigating underwater (Bluefin, 2015).
• Global Positioning System (GPS): A GPS is installed to determine an initial fix and can be used to update the INS when the vehicle surfaces (Bluefin, 2015).
• Ultra-Short Baseline (USBL) Tracking: USBL is a relatively short range tracking system that allows the Bluefin to home to the recovery vessel (AML, 2015).
• Stress, Fault, and Leak Sensors: The Bluefin 21 is equipped with numerous internal fault sensors. For operating at extreme depths, stress and leak detectors alert the AUV of impending structural failure, triggering an emergency ascent (Bluefin, 2015).

Exteroceptive Sensors

• Doppler Velocity Log (DVL): DVL enables the INS to be updated with high frequency water and bottom-referenced velocity, reducing drift. These instruments are limited to around 500m and not practical for deep water operations (TRD, 2013).
• Sound Velocity Sensor (SVS): SVS increases the accuracy of instruments such as DVLs, echo sounders, or anything else that relies on the speed of sound in water for timing calculations (AML, 2015).
• EdgeTech 2200-M 120/410 kHz Side Scan Sonar: The Bluefin-21 can be outfitted with numerous sensors. For the MH370 search, the EdgeTech 2200-M was chosen. This sonar has a depth rating of 6000m with a resolution of 25cm (EdgeTech, 2015), which is suitable for long range searches for large objects.

Answers to Key Research Questions

• What is one modification you would make to the existing system to make it more successful in maritime search and rescue operations?

• I would develop and install a sensor that could fulfill a function similar to look-up/shoot-up on a fighter radar. This would allow the unmanned system to remain in the relatively constant subsurface environment, avoid inclement weather, and conduct wide area scans for life rafts or floating wreckage.

• How can maritime unmanned systems be used in conjunction with UAS to enhance their effectiveness?

• The two systems could either fuse or cue their respective sensors using a datalink. For example, if an RQ-4 Triton identified a point of interest with one its sensors, it could direct the UMS to shift sensors to that point, and vice versa. If a UUV was in use, then it would periodically have to surface to join the network and receive updates. 

• What advantages do unmanned maritime systems have over their manned counterparts?

• The most obvious advantage is that it keeps additional people from entering a potentially hazardous area. Especially in the case of a UUV, the vehicle can be made much smaller (or payload capacity increased) by eliminating a crew compartment and life support systems.

• Are there sensor suites that are more effective on unmanned systems?

• I would propose that the sensors themselves are not more effective, but the unmanned system allows them to get closer to the target at a lower cost, which improves their performance. For example, lets install the same sonar imaging capability of the EdgeTech 2200 on a manned system. First, it could be a surface vessel, which would increase slant range, resulting in decreased resolution. Second, it could be installed on a submarine capable of Bluefin-21 depths, however vehicle would have to be equipped with all the systems needed to support life at 14,000 foot depths.

References

Kaye, B. (2014, April 18). Drone Risks Damage at Record Depth in Search for Malaysian Plane. Reuters Business. Retrieved from http://www.reuters.com/article/2014/04/18/us-malaysia-airlines-idUSBREA3A06W20140418

Bluefin Robotics. (2015). Bluefin-21 Summary. Retrieved from http://www.bluefinrobotics.com/products/bluefin-21/

AML Oceanographic. (2015). USBL / SBL / LBL (Acoustic Positioning). Retrieved from http://www.amloceanographic.com/Technical-Demo/USBL-SBL-LBL_2

Teledyne Technologies Inc. (2013). Workhorse Navigator Doppler Velocity Log. Retrieved from http://www.rdinstruments.com/navigator.aspx

EdgeTech. (2015). EdgeTech 2200 Modular Sonar System. Retrieved from http://www.str-subsea.com/sales/edgetech-2200-modular-sonar-system