If you have to operate side-scan sonars and synthetic aperture sonars (SAS) in very shallow waters (VSW) or shallow waters (SW), the acoustic environment is particularly hostile. Higher order multi-path reverberation, unstable velocity of sound profiles, often unknown, as well as significant bathymetry, baseline decorrelation effects and generally far fewer stable platforms, all add up. The result is far less reliable end sonar products with greater impact to longer range systems. This is particularly acute in tidal and riverine environments. What to do?
Go back to the drawing board
When Solstice was developed in 2010, our technology partner Wavefront Systems decided it was time for a step up in the performance of traditional side-scan sonars. The aim was to deliver a high-frequency, high-resolution, and long-range sonar that would provide a marked improvement in the probability of detection of mine-like objects while minimising the probability of false alarms.
Solstice was designed to do just that. Step one was to design a multi-aperture array which would improve the signal-to-noise ratio extending the range over other sonars operating at the same frequency. However, longer ranges in shallow waters are susceptible to multi-path reverberation. Dr Rob Crook, Research Director at Wavefront Systems explains how Solstice overcomes this problem: “The dominant source of noise for all side-scan sonars operating in shallow waters is ‘multi-path’ reverberation. The nature of this noise means many acoustic pathways scattering from spatially unrelated regions of the underwater scene may none-the-less return to the sensor with identical flight-times. The inability of any ‘2D’ (range, bearing) sensor to discriminate between these contemporaneous pathways leads to an inevitable loss of contrast. Multi-path Suppression Array Technology (MSAT) is a physical array-based technology that offers the swathe coverage one would traditionally have associated with wide elevation beam-widths, with the shadow contrast associated with very narrow beams. MSAT allows high shadow contrast right out to the maximum range of the sensor whilst maintaining high quality imagery close to nadir.” Why is contrast important? It helps to differentiate targets from the surroundings.
In addition, Solstice implements dynamic focusing ensuring that the image will maintain the highest possible resolution at the position in space relative to the sensor, meaning that the resolution will improve as the range to the target decreases. While at longer ranges the interpolated real-time imagery drastically aids human visual perception.
What does it all mean?
The design choices lead to significant advantages for Solstice users. These are some examples of where Solstice excels.
- Simpler to operate: Solstice is simple, the area coverage rate increases with speed while the range remains constant. This makes mission planning easy. You can understand and use the constant range to plot a survey route and you can observe the area that is under consideration. The survey outcome becomes more predictable and simpler to manage.
- More robust: Systems like SAS are known to be very sensitive when mounted on an unstable platform or operating over complex seafloor environments. Any dynamic changes may impact the quality of the SAS data; mud sediments can result in complete loss of micro-navigation data, and in the worst outcome the SAS needs to revert to normal side-scan mode. SAS typically operates at a lower frequencies hence this corrupted SAS side-scan data is not suitable for most operations. Solstice MAS does not share this problem.
- High currents: In MAS the range is limited as a function of the so-called ‘crabbing angle’ but the image quality is preserved along the whole swath.
- Shallow waters: Operations in confined spaces and shallow waters (20m to 30 m depth) are difficult for SAS systems or lower frequency side-scans. These systems can become range limited as the multipath effects from surface returns has an impact on the SNR performance and this is common for all side-scan sonars. For some SAS systems, these effects can compromise as much as 50% of their swath but with Solstice MAS, the impact will typically be less than 10%.
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Leading navies are focused on technological innovation, but it is time to outpace the rate of technological change. It is time to go further than partnerships. In this article Ioseba Tena, Commercial Director at Forcys, challenges navies to go further than ever before.
In the past, the introduction of new naval technologies has been driven and dictated by navies themselves according to changing mission requirements and their understanding of the technology available. But within the evolving threat landscape, navies are starting to embrace the incessant pace of technological change by sharing more with industry. This sharing is essential if you need to develop and leverage new technologies to address present and future threats.
Threats are swiftly evolving, unpredictable and varied. Traditionally, drones were largely confined to the aerial domain. Now, unmanned underwater vehicle (UUV) threats are evolving rapidly. You must quickly develop and integrate the technologies and expertise to protect crews, vessels and critical infrastructure.
The common causes of protecting people from attack and the environment from disaster unite academics and navies. While there is some collaboration, the two communities often operate separately. Academia can be tasked to drive focused innovation, but these institutions are neither motivated nor incentivised to fund the production of fully formed security solutions. That means involving defence suppliers at the earliest possible stage in concept discussions. The best innovation will come from a well-grounded understanding of the size and scale of the challenges. Project risk, which invariably manifests itself as increased costs and time, could be reduced by inviting industry to embark in vessels to see the operational challenges first hand (a way perhaps to break the old cliché of waiting too long and then not getting what you actually needed!)
In the underwater domain, identifying, classifying and neutralising threats poses numerous challenges, largely because contacts underwater are notoriously difficult to evaluate. Intruder detection is difficult due to poor visibility, variable terrain, noise and the presence of other objects in the water such as marine life or debris. It’s no longer just large, manned, submarine platforms either; the threat could come from combat divers who are small and very quiet, or UUVs which are faster and therefore difficult to track.
It’s for this reason that naval forces cannot be islands. To gain a battle-winning advantage and neutralise threats, whether from the air or the sea, collaboration across industry, government enterprise and academia is a recognised necessity. Together we need to work towards a capability ecosystem that supports and promotes the swift and successful development of new technologies, enabling us to stay ahead of emerging threats and maintain operational advantage. This ecosystem goes beyond a narrowly-defined partnership. Industry, academia and navies must learn to communicate, innovate and learn from each other in order to ensure that forces on the front line have the necessary capabilities to carry out safe, successful operations.
Did you know that Forcys is the result of partnership between leading instrument vendors in the underwater domain? That’s why we understand that the ecosystem described above is key to the success of technology innovation. Our technology partners already have a strong legacy of working with industry, academia and government organisations. We continue to proactively look to forge relationships with academia to deliver the solutions to meet your needs, on time and on budget. Forcys and our technology partners can leverage university resources and insights to inform the next generation of technology, products and services for its customers.
For example, our technology partner Sonardyne is currently collaborating with Newcastle University on a new open standard in underwater communications. The standard, named Phorcys and funded by the Defence Science and Technology Laboratory, is a high-integrity secure waveform for underwater acoustic communications. Another good example is the collaboration between our technology partner Voyis and McGill University. They are producing a new generation of optical processing techniques for illuminating the underwater domain. Both projects have been primed with knowledge and experience from the commercial sector. The latest step is applying the technology to naval applications. At which point you will be able to find off-the-shelf technologies that meet naval capability requirements.
Government agencies and navies are increasingly recognising the importance of secure, open standards to begin using commercial-off-the-shelf (COTS) components. As you know it’s critical to minimise project risk. How? By applying extensive knowledge and expertise in underwater communication and location technologies. Our technology partners have been at the heart of no-fail delivery for commercial customers for over 50 years. This means we have the expertise to deliver allied forces the interoperability needed to conduct successful operations at home and overseas.
At Forcys we are interested in talking to anyone who would like to be part of an ecosystem driving naval technology innovation. We want to create the best defence systems in the world. Invite us to see the problem and discuss your needs.
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