By Brett Chereskin
Abstract
This paper provides an explanation
of the sensors and capabilities of the Bluefin-21 autonomous underwater vehicle
(AUV). There are four topics address within this paper. The first is an
analysis of marine sensors that support underwater search and rescue. The
second topic proposes modification to the AUV that would increase search and
rescue capability. The third topic proposes possible sea to air unmanned system
coordination, and the final topic weighs the pros and cons between manned and
unmanned systems in maritime sensor technology.
Introduction
The Bluefin-21 is an autonomous underwater vehicle (AUV) that is
build by Bluefin Robotix. This advanced maritime AUV has recently been used in
the search for Malaysia Airline flight MH370 and contains many sensors that are
perfectly suited to the underwater search and rescue mission (Chand, 2014). Understanding
the available sensors used on the Bluefin-21 will help determine if any
modification can be made that will increase it’s capabilities as well as if
integrating with unmanned aerial systems (UASs) could provide an increase to
its mission success. Additionally, by analyzing the advantages of sensors
suited to unmanned systems a clear understanding of this topic will be
gained.
The Sensors of Bluefin-21
The Bluefin-21 can be fitted with multiple
sensors depending on the mission requirement. One of the most commonly used
sensors for maritime search and rescue on the Bluefin-21 is the EdgeTech 2200-M
120/410 kHz side scan sonar (Chand, 2014). The EdgeTech 2200-M gathers side
scan and/or sub-bottom data using EdgeTech’s proprietary technology in water
depths up to 6000 meters (EdgeTech, 2015).
This proprioceptive sensor is specifically deigned for use in the
maritime environment due to the fact that only in water will acoustic/ FM sonar
sensors provide the best wave propagation and resolution. To note, one of the greatest advantages of
this particular sonar imagining sensor is that is uses full spectrum signal
processing that sends out a broad band transmitting pulse. One benefit of a
full spectrum system is the relative power savings over a conventional
continues wave sonar system. In order to obtain the same resolution, conventional
sonar would required 100 times more power compared to the full spectrum sonar
system (EdgeTech, 2015).
Possible Modifications
Upon analysis of the EdgeTech 2200-m on the
Bluefin-21, other than attempting to decrease weight and power consumption,
which are key to any unmanned system, I propose that the ability to network
multiple sensors via underwater acoustic networks should be integrated. Due to
the temporal constraints of any search and rescue mission, being able to cover
larger amounts of area in less time is essential. The Bluefin-21 uses an INS to
accurately track its positions, but allowing the position data to georeference
the EdgTech’s imagery would be the first step in the multi-sensor integration
(Bluefin-21, 2015). After georeferenceing, multiple sensors would need to
communicate the data in order to run algorithms that would optimize participating
AUV tracks so the multi-sensor system could map the largest possible area the least
amount of time.
Aerial Integration
In
order to network multiple sensors via underwater acoustic networks,
consideration must be made to the limitations of acoustic communication networks. Underwater acoustic communications are
generally recognized as one of the most difficult communication media in use
today (Stojanovic, 2009). Due to this limitation, an alternative could be the
introduction of an aerial command and control node, specifically an unmanned
aerial system capable of extended transit and loiter times as well as beyond
line of site communication of high bandwidth datasets. The multiple
Bluefin-21’s could surface at regularly scheduled intervals and upload key data
to the command and control UAS. The UAS would not only send the AUVs datasets
to the mission command center at real near time, but it could also provide
mission parameter changes to all other AUVs participating in a particular
mission set.
Unmanned vs Manned
In
terms of maritime sensors, there are a few key reasons why the use of AUVs over
manned systems is beneficial. One major reason has to do with sensor depth. In
terms of maritime sensor operation, it is known that attenuation of sonar
pulses and noise are a limiting factor in obtaining high-resolution products (Stojanovic,
2009). If sensors were limited to shallow depths due being mounted on manned
systems, the resolution during deep-water search and rescue would be limited.
If the system is mounted on an AUV like the Bluefin-21, which is capable of
diving to 4500 meters, it would be able to retrieve higher resolution products,
and possible dive deep enough to obtain true camera imagery of the bottom of
the ocean (Bluefin, 2014).
Conclusion
The
integration of unmanned systems into maritime search and rescue has taken
previously existing sensor technology to the next level. The ability to take
these sensors deeper and coordinate and optimize multi-sensor operations will
save lives in the near future. By further integrating the unmanned aerial layer
into the maritime layer, it will speed up data transfer and facilitate ad hoc
mission changes.
References
Chand , N. (2014). Unmanned/Autonomous Underwater Vehicles. SP’s
Naval Forces, Jun 2014 Issue. Retrieved from http://www.spsnavalforces.com/story.asp?mid=37&id=6
EdgeTech Corp. (2015). 2200-M
Modular Sonar System. Retrieved from
BlueFin Robotix Corp. (2015). Bluefin-21
Summary. Retrieved from http://www.bluefinrobotics.com/products/bluefin-21/
Stojanovic, M., & Preisig, J. (2009). Underwater
Acoustic Communication Channels Propagation Models and Statistical
Characterization. IEEE Communications Magazine Retrieved from http://web.mit.edu/millitsa/www/resources/pdfs/chmj-print.pdf
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