The Next Wave - Swarming Underwater Drones

Experimentation with large numbers of low cost quadrotors operating in swarms has produced some interesting results, including potential for future military applications.  Now some researchers in Germany are working to transition these concepts to the underwater realm, building autonomous underwater vehicles (AUVs) that behave like fish in a school.  A team at the University of Luebeck's Institute of Computer Engineering has developed an affordable AUV designed for environmental surveys called MONitoring System and Underwater Navigation Robot (MONSUN) II.

MONSUN II is a 4 kilogram AUV equipped with a series of vertical and horizontal thrusters to maneuver and maintain orientation.  The vehicle maintains its position relative to other AUVs in the school using infrared sensors and a nose camera with a form of computer image recognition called "blob detection." 

The swarming technology demonstrated by MONSUN vehicles is designed to overcome several of the limiting factors inherent in unmanned underwater vehicles. The most important capability a swarm brings AUVs is redundancy. Rather than relying on a singular, expensive platform, MONSUN uses a number of low-cost, homogenous robots that can alter their role within the swarm.  While a portion of the AUVs conduct tasks underwater, the others act as communication relays.  If one of these vehicles has a mechanical failure or is lost, the swarm continues to operate.

Another challenge with conventional AUV operation is underwater navigation.  Because at least one of the AUVs will always be at the surface, the entire swarm can get an idea of its position relative to the fix from the surfaced vehicle's GPS. Currently, MONSUN uses very short range infrared sensors to maintain the relative position of each vehicle, but eventually, the vehicles will be equipped with acoustic modems capable of communicating with each other out to approximately 50 meters.  A second well known UUV issue is limited duration and energy consumption. The MONSUN AUVs are positively buoyant, so the surfaced vehicles can save battery power by turning off their vertical thrusters and cameras. In this manner, the energy load is balanced throughout the swarm, leaving the vehicles underwater to continue their surveys, and extending the mission duration for the entire swarm. The surfaced vehicles can also transmit data collected by the swarm to a ship or other base.

Surfaced AUVs acting as relays provide position data to the swarm.
In tank testing, the Luebeck researchers have demonstrated cooperative vehicle behavior using two of the AUVs (see above video). More complex swarm algorithms have been examined virtually with the Institute's Marine Robot Simulator.  Future improvements are planned for the software that integrates the AUVs cooperative behavior and the vehicles themselves.

This technology is interesting, and has likely scientific uses, but what about naval applications?  Force protection hull inspections  are a common task for explosive ordnance disposal divers and increasingly ROVs.  These dives require a methodical, meter by meter inspection of a ship's underwater surfaces, usually in the dirty, low visibility water of a sea port.  A dozen low-cost AUVs may be able to inspect larger numbers of ships in busy ports as they come and go.

The advent of unmanned systems continues to reduce the risk to sailors performing mine countermeasures, but these operations remain extremely time consuming. Large numbers of smaller AUV's operating together in a swarm might enable more rapid localization and identification of sea mines in a given area, allowing higher end, specialized UUVs to positively identify and neutralize them.

In the future, the ability of AUV swarms to dwell quietly, execute a coordinated hunt, and mass for an attack may enable some interesting offensive capabilities.  One tactic might involve air dropping a group of AUVs into a choke point before an enemy ship transits.  Like current generations of smart mines, the AUVs could listen silently and discriminate between targets and neutral shipping based on acoustic or other signatures.  Unlike mines however, the AUVs would move to thwart detection and mass to envelop a ship with small shaped charges.

Similarly, in an anti-submarine warfare role, underwater drone swarms could operate as a mobile sonobuoy fields, repositioning through various acoustic layers in response to the movement of a target sub, and relaying their tracking data to air platforms to prosecute the submarines.  

Sooner or later, much as UAV technology has become accessible to the masses, so will cheaper AUVs.  The resulting technical and tactical experimentation will be interesting to watch.


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