Bluefin-21’s Sensors and Advances in Maritime Sensors

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 

            http://www.str-subsea.com/file_download/22/EdgeTech+2200+Modular+Sonar+System.pdf

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

Article Summary of "Electro-optical sensor payloads for small UAVs"

During my pursuit of a Masters in Unmanned Systems, the topic of shrinking sensors to fit small UASs came up in a discussion during class. I decided to search the internet to see what information could be found. Below you will find a summary of an article that address the constraints and challenges of fitting Electro-Optic/ Inferred (EO/IR) sensors on small UASs.
   
The following is a summary of article titled "Electro-optical sensor payloads for small UAVs" which could be found at this LINK.

This photo shows the relatively small size of the ScanEagle UAS which was studied in this article

Summary: 

Development in unmanned systems has been increasing exponentially over the past few years, and the sensors that accommodate these systems are progressing as rapidly as the systems themselves. Development is occurring in ground and marine based unmanned systems, but the requirement to shrink sensors is truly a requirement coming from the airborne sector of the unmanned world. In the world of small UAS, grams of payload directly correlate to proportionally large amounts of loiter time.

In the past, EO/IR sensors were developed for large UASs, low flying helicopters, or large manned platforms. Today, the developments in small UASs, both in the civilian and military sectors, have created a paradigm shift in the development of these EO/IR sensors. Previously, developers of EO/ IR sensors were able work "off the shelf" camera technology into operational, multi-function payloads. Today, due to the shrinking size of the air vehicles and changing mission requirements, engineers have begun to focus on building light weight solutions from ground up. This has allow requirements to truly drive development, and new EO/ IR sensors are not only lighter, but more effective for future unmanned missions. 

The author uses two examples to highlight how a paradigm shift in engineering and a fundamental change in thinking altered small UAS sensors. The first example utilizes the change from uncooled to cooled EO/IR sensors. Originally, the use of improved glass optics and uncooled IR systems cut weight and would provide adequate mission accomplishment. Today, the capability of small UASs has increased as well as the altitudes they are able to fly, and the additional weight associated with a cooled system now outweighs the limitations of the uncooled variant. The other example studies the transition from the lightweight and less precise 2 axis stabilization system to a 4 axis stabilization system. Like the cooled vs uncooled scenario, the increase in small UAS capability through UAS specific engineering requires a more stable platform which is more capable of allowing higher precision payloads to be carried.    

The article concludes by discussing how the shrinking of what were once only large UAS sensors will bring advanced functions like 3D mapping into smaller and more affordable system. Not only will the airborne systems benefit, but both ground and marine systems will benefit as well.  


Brett Chereskin