Pier-Side, Bow Sonar Calibration Methodology for Wave Piercing Hull Forms Navy SBIR FY2006.2 Sol No.: Navy SBIR FY2006.2 Topic No.: N06-139 Topic Title: Pier-Side, Bow Sonar Calibration Methodology for Wave Piercing Hull Forms Proposal No.: N062-139-0485 Firm: Applied Physical Sciences Corp. 475 Bridge Street Suite 100 Groton, Connecticut 06340 Contact: Jason Rudzinsky Phone: (860) 448-3253 Web Site: www.aphysci.com Abstract: The DD(X) destroyer relies on sophisticated, dual frequency bow sonar for mine-avoidance, ASW, and torpedo defense. Existing approaches to in situ bow sonar calibration that use booms to extend hydrophones beyond the sonar, along with legacy nearfield-to-farfield projection algorithms, will not work for DD(X) due to the ship's strict radar cross section requirement and unique hull and sonar array shapes. Here we propose an innovative calibration system for the DD(X) bow sonar's mid- and high-frequency components - both transmit and receive - which can be utilized pierside or in a harbor setting. The proposed system features three main components: a nearfield transducer array used to measure the sonar's transmitted fields and to ensonify the sonar's receivers; algorithms to accurately project the nearfield responses to the farfield; and an acoustic positioning system which eliminates the need to fix the nearfield array to the hull. The nearfield array is comprised of multi-mode transducers, which can operate in both omnidirectional and dipole modes. In Phase I, we'll mature the proposed algorithms, develop a preliminary system design, and specify deployment and quality control concepts. Benefits: Maintaining high performance of sophisticated sonar systems is a critical aspect of current and future naval missions. Advanced target localization, tracking and classification algorithms can be sensitive to errors originating at the sonar. For example, APS is developing a mine localization algorithm for the DD(X) bow sonar under separate SBIR funding (Topic N04-218). This localization algorithm relies on accurate estimates of the vertical angle of arrival of multipath returns from a target. Errors in the sonar calibration can compromise the direction-of-arrival estimator and in turn, degrade the performance of the localization algorithm. Additionally, existing approaches to in situ calibration of various Navy sonars, which in principle eliminate the need to test the sonar at a dedicated test facility, are not appropriate for modern hull shapes and sonar calibration requirements (e.g., the need to know detailed beampattern information). The system developed here would allow for intermittent recalibrations while a ship is pierside anywhere in the world and would provide sufficient detail to provide for advanced diagnostics and assessments of the effects of sonar distortions on advanced sonar signal processing algorithms. The system concept proposed here can easily be migrated for use with commercial sonars (e.g., multibeam bathymetry survey sonars) and could potentially be a featured in situ sonar calibration service to the commercial shipping industry. Return