This Article is provided as a backgrounder to the news Release from Kraken Sonar Systems Inc on their acquisition of all Intellectual Property (IP) rights to the AquaPix® Synthetic Aperture Sonar (SAS) technology platform from Marport Deep Sea Technologies Inc. To Read the news release CLICK HERE
A number of different underwater activities rely on high quality seabed imaging. Offshore exploration, ocean science, seabed mapping and military missions are examples of applications with growing demands for better seabed image resolution.
Until recently, sidescan sonars and multibeam echo-sounders have been the leading technology for detailed mapping and imaging of the seafloor. However, Synthetic Aperture Sonar (SAS) provides ultra-high image resolution with superior area coverage rates. This technology is now commerciallky available from Kraken Sonar Systems Inc. a marine technology company engaged in the design and development of high performance SAS and Acoustic Velocity Sensors for military and commercial applications.
SAS offer high resolution imagery at longer ranges than conventional side-scan sonars. This is done by replacing traditional sonar hardware with sophisticated signal processing software. The principle of SAS is that the receive transducer array is synthesized in software by the coherent recombination of many sonar pings overlapping an area of interest. This represents a major savings in sonar hardware and enables much higher resolution than is possible with conventional sonars.
Synthetic Aperture Sonar provides constant image quality unmatched by conventional sonars and is a key technology whenever high resolution is required. In addition, Interferometric SAS (InSAS) can deliver high quality 3D bathymetric images that meet the demanding standards for todays hydrographic surveys. AquaPix® can provide highly detailed seabed imagery (3 cm) out to a range of 300m from each side of an underwater vehicle (600m swath). The bathymetric data resolution exceeds 25cm to full range while delivering very high depth accuracy, and is in compliance with IHO S44 special order requirements.
Interferometric SAS is strongly related to its airborne cousin – interferometric Synthetic Aperture Radar (SAR). While interferometric SAR has transitioned into a commercial off-the-shelf product, interferometric SAS has for a long time remained at the research stage. Some of the reasons for this delay have been the challenges in obtaining very high navigation accuracy through the ocean, as well as the high-computational cost of SAS imaging software. The introduction of stable unmanned underwater vehicles, cheaper and more powerful data-collection and processing electronics, combined with advanced micro-navigation and auto-positioning methods has recently brought Interferometric SAS forward as a viable alternative to conventional side scan sonar.
A further by-product of Synthetic Aperture Sonar is a highly accurate ground velocity estimate that holds great potential for underwater vehicle navigation. Such micronavigation limits the drift of aided inertial navigation systems and significantly improves positional accuracy requirements for long endurance seabed surveys. Kraken also has plans to develop a series of acoustic velocity sensors using SAS techniques.
SAS hardware (transducer arrays and electronics) and signal processing have been a research topic at the NATO Undersea Research Centre (NURC) in La Spezia, Italy for many years. For over 12 years, this research effort was led by Dr. Marc Pinto, who now serves as Krakens Chief Technology Officer.
He has participated in the development of SAS since the early 1990s and holds two SAS technology patents, has authored 50 related publications and is recognized internationally as a subject matter expert. Prior to NURC, Dr. Pinto was the Head of the Advanced Sonar Studies Group at Thales Underwater Systems in Brest, France specializing in advanced mine countermeasures sonar including SAS.
His recent research led to the development of the AquaPix® Interferometric Synthetic Aperture Sonar. In parallel with the hardware design, Dr. Pinto and other sonar scientists at Kraken have developed a powerful signal processing software application called INSIGHT (INterferometric Sas Imaging Georeferenced High-fidelity Toolbox) thats used to produce highly detailed seabed images with co-registered 3D bathymetric data.
The AquaPix® sonar system engineering effort was led by Sean Chapman, Krakens Chief Sonar Engineer. Mr. Chapman joined the U.K. Defence Research Agency in 1984 and served as technical leader of DERAs SAS development program. Prior to Kraken, he served as Chief Sonar Engineer for Ultra Electronics UK.
Both AquaPix® and INSIGHT were developed by Krakens team of scientists and engineers in a record time span of under 18 months. The first system was successfully trialed in Halifax, Nova Scotia in August, 2012 onboard an ISE Explorer AUV owned by Defence Research & Development Canada. Successful sea trials have since been carried out with other military organizations in both cold and warm water environments and integrated onboard several different types of Autonomous Underwater Vehicles.
The innovative sonar design exploits a dual row frequency multiplexed transducer array enabling on-the-fly selection of the vertical beamwidth of both the transmitter and the receiver in order to optimally suppress multipath. Two beams with different beamwidths are transmitted at the same time, at different frequencies, and the best beam is dynamically selected by frequency filtering, a technique inspired from Orthogonal Frequency Division Multiplexing (OFDM) techniques used in radio communications. The multiplex also provides the high level of spatial overlap required to robustly implement adaptive focusing techniques.
The AquaPix® sonar solution is modular in design, using broadband piezo-composite ceramic arrays which are fully encapsulated for robustness against harsh environments. The use of piezo-composite ceramics not only provides unsurpassed bandwidth and flexibility, but also delivers repeatability in manufacture of sonar arrays with precisely defined beam patterns to provide the spatial filtering crucial to achieving high performance. Transmit and receive electronics are also fully encapsulated within the sonar array modules, with small, flexible cables for connectivity to a host pressure vessel.
The pre-amplifiers and sampling rates exploit many years of SAS science and engineering development and achieve true 24 bit sampling with a power consumption of less than 150mW per channel. The transmit electronics achieve 97% efficiency, with fine phase and amplitude control. The modular arrays are designed to be integrated into a range of unmanned maritime platforms such as Autonomous Underwater Vehicles (AUV),
Other features and capabilities of the AquaPix® system include:
- Ultra-high resolution – 3cm across entire swath
- Swath widths of up to 600m 15x sonar altitude
- Superior area coverage rate
- Low to high speed operation
- Shallow water to full ocean depth
- Co-registered imagery and 3D bathymetry
- Advanced sonar array design mitigates multipath
- Very tolerant of UUV yaw / crabbing action
- Low cost
- Modular design integrates to AUV, ROV, ROTV and towfish
- Superior image resolution and area coverage rate over SSS
- Compliant to IHO SP44 hydrographic survey standard
- Interfaces to industry-standard visualization software
- Robust sonar design uses latest technologies
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About Kraken Sonar Systems Inc.: Kraken is a marine technology company engaged in the design and development of high performance Synthetic Aperture Sonars and Acoustic Velocity Sensors for military and commercial applications. For more information, please visit: www.krakensonar.com
About Marport Deep Sea Technologies Inc.: Marport is an award-winning designer and manufacturer of sonar systems and sensors for underwater defence and commercial fisheries. For more information, please visit: www.marport.com
FOR FURTHER INFORMATION PLEASE CONTACT:
Kraken Sonar Systems Inc.: Sheri Squires, Communications Coordinator, (709) 757-5757 extension 288; firstname.lastname@example.org
Marport Deep Sea Technologies Inc.: Cyril McKelvie, President and CEO, (613) 287-2011; email@example.com