APL Colloquium

December 7, 2001

Colloquium Topic: On Environmental Limits to Sonar Performance

The primary objective of the forth-coming Office of Naval Research (ONR) Acoustic Observatory (AO) Robust Passive Sensor (RPS) Project is the exploration of, first, the environmental space-time coherence properties of acoustic propagation and, second, dynamic shipping interference. It is postulated that these two mechanisms jointly may impose the upper performance bound on future low frequency passive sonar systems in the littorals. The scientific and technological objectives of this effort are: (1) to develop environmentally matched spatial aperture design methods (topology); (2) to provide a calibrated test-bed facility to establish the absolute performance dB budget for existing and future high gain sonar systems and (3) to develop passive sonar adaptive beamforming (ABF) algorithms for high traffic areas where performance is limited by high bearing rate sidelobe and mainlobe interference. An implicit RPS goal is to create a sonar system self-assessment module that continuously evaluates the performance of sonar and adaptively matches both the available array aperture utilization and processing algorithms to the presumed bottom-limited, time variable and discrete shipping rich environment. The objectives include, first, the development of a real-time array performance dB budget assessment procedure and, second, the control of adaptive beamformer (ABF) parameters to provide robust and computationally efficient spatial processing. In this presentation, the measurement of horizontal propagating wavefront coherence distance and its role as a limiting factor in large aperture Array Signal Gain (ASG) performance is discussed. The relation of ASG to the optimum design of the array aperture is considered. Likewise, the importance of estimated Array Noise Gain (ANG) in matching an ABF configuration to the shipping interference environment is considered. Accordingly, the prediction of performance of a high gain array with adaptive nulling of loud commercial shipping traffic is presented. This prediction is based on a simple omni-directional hydrophone measurement of the ambient noise floor and relative shipping sound pressure levels. Finally, an overview is given of the planned AO facility and its relation to the performance of future high gain sonar systems.

Colloquium Speaker: Norman Owsley

Dr. Norman Owsley received the B.S.E.E. (¹63) from Lehigh University, and the M.S.E.E. ('65) and Ph.D. ('68) from Duke University where he was a NSF Intern and held a NASA fellowship working on the Mariner Mars probe adaptive FSK telemetry system. In 1968, Dr. Owsley joined the U.S.Navy Underwater Sound Laboratory, working on adaptive signal processing methods for both active and passive sonar. He was a NATO Exchange Scientist to Norway and was awarded Special Achievement Awards in Engineering and Science, the Naval Undersea Systems Center (NUSC) Chair in Signal Processing, the Navy Meritorious Service Award, the American Defense Preparedness Association Bronze Medal, the NAVSEA Scientist of the Year, the American Association of Naval Engineers Gold Medal, the Federal Laboratories Award for Technology Transfer and the ONR Capt. Robert Conrad Award. He holds eight US patents, has published fifty articles and papers and co-authored the book Array Signal Processing published by Prentice-Hall. Dr. Owsley¹s work during his Navy career has spanned all aspects of high performance sonar, array design and acoustic communications. He was the innovator of the Multiline Towed Array technology which is currently scheduled for a NAVSEA Advanced Sonar Technology Office(ASTO) Advanced Development Model sea trial in 2002. Dr. Owsley is a Fellow of the Institute of Electrical and Electronic Engineers (IEEE). In 1999, he retired from the Navy and spent the next two years at the MedAcoustics Corporation developing an acoustic heart sound analysis. In 2001, Dr. Owsley became a Research Professor at the University of Rhode Island and is currently supporting the ONR Ocean Acoustic Observatory Shallow Water Testbed Project as an IPA assignee.