Sea Technology

NOV 2018

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14 ST | November 2018 Norwegian Defence Research Establishment (FFI). These and follow-on studies informed the design of a number of SAS systems, including: the CMRE MUSCLE, which was built by Thales Underwater Systems and continues to provide a common research platform for the NATO MCM JRP; the DERA/QINETIQ technologies, which were later acquired by ATLAS ELEKTRONIK and evolved into the Vision family of systems; the Kongsberg/FFI HISAS system, with early developmental emphasis on improved SAS motion estimation by sonar micronavigation aiding of the INS; and the Kraken MINSAS family of systems, developed for broad application across the maritime marketplace. Other European suppliers of SAS systems include the companies Ultra Electronics and iXblue. SAS Development in the Asia-Pacific Region Many of the U.S. and NATO systems discussed in this article have been heavily influenced by the studies, innovations and subject matter experts originating from the Acoustics Research Group (ARG) at the University of Canterbury in Christchurch, New Zealand. The ARG, active since the early 1980s, has conducted synthetic ap- erture research that includes measuring acoustic phase stability in the ocean medium; exploration of continuous transmission frequency modulation (CTFM) for simplified broadband processing; development and evaluation of efficient image reconstruction algorithms and data-driv- en autofocusing; and methods of SAS interferometry. Development of experimental synthetic aperture so- nar systems has been undertaken by researchers in China and Japan since at least the late 1990s. Low-frequency systems were developed in the early 2000s by the In- stitute of Acoustics, Chinese Academy of Sciences and partners and, separately, by the NEC Corp. Since 2000, the Japan Agency for Marine-Earth Science and Technol- ogy (JAMSTEC) and partners have developed a series of towed SAS systems, which have been used for geologic mapping. Current, Future Trends Currently, more than a dozen nations have developed, are developing or have procured synthetic aperture so- nar systems, with several North American and European families of systems beginning to see widespread use. An active R&D community, empowered by the maturation of SAS technologies worldwide, has been developing new capabilities that include: SAS interferometry for high-res- olution bathymetry, extended ranges, circular SAS tomo- graphic imaging, buried munitions mapping, automated target recognition and change detection, and through- the-sensor characterization of the ocean environment. Improvements in materials, transducers, electronics and processing will lead to new uses that include exploita- tion of frequency agility and increased bandwidth, cali- brated data products (e.g., direct estimation of target or backscatter strength), as well as continued reduction in the size, weight, power and cost of these systems. Synthetic aperture sonars are currently being fielded in areas that include geological mapping, infrastructure surveys, environmental remediation, marine salvage and archaeology, and mine countermeasures. If the current trend of innovation is any indication, the number and va- riety of SAS-based applications will continue to grow, re- sponding to increasing demands for precision, wide-area mapping and greater understanding of the undersea en- vironment. Acknowledgments We thank Jose Fernandez and Dr. John Lathrop for sharing their vast knowledge and memories of SAS devel- opment at NSWC PCD, Tony Waterman for his consider- able support locating historical documents in the NSWC PCD Technical Library, and members of the SAS R&D community who kindly shared their insights and reviews of this article. References For a list of references, contact Daniel Sternlicht at ST Dr. Daniel D. Sternlicht is the distinguished scien- tist for littoral sensing technologies at the Naval Surface Warfare Center Panama City Division, leading new developments in maritime recon- naissance and surveillance for Navy and Marine Corps missions. He received a Ph.D. in electrical engineering and applied ocean science from the University of California, San Diego, and Scripps Institution of Oceanography. Dr. Michael P. Hayes is an associate professor at the Department of Electrical and Computer En- gineering and head of the Acoustics Research Group at the University of Canterbury, Christ- church, New Zealand, where he also received a Ph.D. in electrical and electronic engineering. Dr. Roy E. Hansen is a principal scientist in syn- thetic aperture sonar and AUV development at the Norwegian Defence Research Establishment (FFI). He is also an adjunct professor in acoustic imaging at the Department of Informatics, Uni- versity of Oslo, Norway. He received a Ph.D. in physics from the University of Tromsø, Norway. "If the current trend of innovation is any indication, the number and variety of SAS-based applications will continue to grow, responding to increasing demands for precision, wide-area mapping and greater understanding of the undersea environment."

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