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Pixel-Perfect Imaging

By Nick Swift

Recent trials have produced this high-resolution image of a wrecked tug vessel. This image was taken in a single run of the site, in water depths of approximately 7 meters.
Although AUVs have been more routinely deployed for military, maritime security, oceanographic research, mapping, environmental monitoring and other underwater surveying applications, the sonar technologies that they are equipped with have yet to be fully optimized. However, Solstice—Sonardyne's (Yateley, England) new generation of search-and-classify side scan sonar with integrated swath bathymetry—has been developed without compromise for AUV deployment and specifically optimized for shallow-water environments.

Considerable market research has revealed that users not only want a system that will compete with the resolution and performance of a synthetic aperture sonar (SAS), but also has the operational benefits and costs associated with conventional side scan. Additionally, it should be ultralow power to increase the operational capability of the host platform and modular, enabling the system to be optimized for any platform, large or small. Equally important is the ability of the system to be operable by a broad range of users, providing a new capability for applications as diverse as habitat monitoring and broad change detection in maritime security scenarios.

To understand Solstice, one must put aside any preconceived ideas about side scan. Sonardyne has created a seabed imaging tool that has transitioned some of the juicy bits from SAS technology, such as auto-calibration and back-projection imaging, into a new design that rivals the SAS system for performance but can be operated as simply and cost effectively as a conventional side scan.

Designed for use on a variety of underwater platforms, Solstice is a low-power (only 18 watts), compact sonar that provides world-class imagery and coregistered bathymetry of the seafloor beneath it (±100 meters swath width). Although optimized for deployments between 7 and 10 meters above the seabed, Solstice can perform well anywhere from 4 to 20 meters. In particular, real-world trials have shown that Solstice is able to provide bathymetry in extremely shallow-water areas (even down to 2 meters) where the use of multibeam systems would be hazardous and time consuming.

The imagery produced by Solstice is designed to be of the highest quality possible from conventional sonar. The sonar provides a high-fidelity image by using a back-projection beam-forming technique to focus at every single pixel in the image, unlike most conventional side scans that have a fixed focus. In addition, several other proprietary technologies (array real-time auto calibration, multiping integration and image stabilization) allow Solstice to continue providing this high-fidelity imagery, even as platform stability and acoustic conditions deteriorate. This is often the case with shallow-water deployments on smaller vehicles. However, the unique Solstice array design gives unparalleled performance in shallow-water environments, maintaining 100 percent ground coverage.

Testing, Trials and Integration
This year, the development program reached a major milestone as it moved from engineering development to delivering the first production units to customers. One such customer is Bluefin Robotics (Quincy, Massachusetts), developer, builder and operator of AUVs and related technologies for defense, commercial and scientific customers worldwide.

Solstice has been integrated with a Bluefin-12 AUV, a model most commonly used for offshore survey, search and salvage, environmental monitoring and unexploded ordnance survey operations. The free-flooded and modular mechanical design of the Bluefin-12 makes it an ideal candidate for the quick integration of payloads for rapid test and demonstration. These elements combine to create a flexible hardware, software and electrical interface that allows for the integration of new payloads with minimum development work. The Bluefin-12 is available in 1,500-meter and 200-meter depth-rated models, each with the ability to integrate flexible payload arrangements based on individual mission requirements. To continue this article please click here.

Nick Swift is a qualified business development manager, with extensive experience across the defense and energy markets and a master of business administration degree. Prior to becoming head of the maritime security division at Sonardyne in 2012, he held commercial responsibility for the company's geophysical products and markets.

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