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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.

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Lobster pots (approximate dimensions 800 mm x 400 mm) observed at different ranges using Solstice (Image courtesy of GDMS)

Please contact us to find out more.

In brief

Just because your expeditionary forces operate small Autonomous underwater vehicle (AUV) systems, it doesn’t mean they should not be ambitious as to which payloads to carry. When deploying from a Rhib or other confined spaces, then low-logistic one-person operated instruments are a necessity. This requirement has seen the proliferation of small AUVs. In January of 2022 a number of this units manufactured by OceanScan-MST were delivered to Denmark’s Frederikshavn naval base. Though the AUVs are small, their payload requirements weren’t.

The challenge

The customer wanted to equip these AUVs with the latest generation of 4K digital stills cameras and 3D lasers. Fitting the equipment to an AUV already packed with sonar payloads and other navigation instruments is challenging. Fortunately our technology partner Voyis and their next generation optical systems were at hand. They had to work closely with OceanScan-MST to understand the constrains and develop the right mechanical design to integrate the popular Recon LS System.

The solution

The solution was to develop an OEM version of the Recon LS where each of the components was delivered and carefully integrated to the AUV. The integration to the platform is of paramount importance as the product has been very carefully designed to optimally illuminate the scene.

The result

The Light Autonomous Underwater Vehicle (LAUV) supplied by OceanScan-MST were equipped with an identification capability enabling each of the AUVs to search for contacts with the combined sonar and laser pair and enabling re-acquisition with the same AUV. This means improved probability of detections, increased area-coverage-rates and mission tempo and imaging with an amazing fidelity to support other missions beyond mine countermeasures.

If you would like to know how Forcys and its technology partners can support your expeditionary needs please do not hesitate to get in touch.