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Low Frequency Active Sonar (Generic UK) Performance Assessment in the Operationally Significant Area of the Northwest Approaches to the United Kingdom

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Master's thesis

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The goal of this research was to make a performance assessment for a generic UK Low Frequency Active Sonar LFAS operating in the northwest approaches to the UK. Five diverse and operationally significant sound speed and geoacoustic transects of the region in winter and summer were considered. The intention was to use an operational, ray theory based, acoustic propagation loss model for the performance assessment at 400 Hz and. 800 Hz for various sourcetarget depths. Prior to the assessment the ray model was compared with a finite element primitive equation transmission loss model RAM to, firstly, validate the propagation loss algorithms, and, secondly, to make any required corrections to the ray model propagation loss output as a result of variable geoacoustic conditions. Results show that the ray model compares favorably with RAM and only minor corrections were required. RAM was also used to evaluate the effect of the South East Icelandic Front in summer on acoustic propagation at the frequencies of interest. Results demonstrate that, depending upon sourcereceiver dispositions, the inclusion of range dependent sound speed profiles and geoacoustic parameters are a necessity. LFAS performance results demonstrate that the system is able to achieve good results with lower frequencies performing better than high frequencies. However, high reverberation levels are a severe limiting factor. Investigation into advanced signal processing techniques suggest that the utilization of inverse beamforming techniques has the potential to improve detection opportunities by suppressing reverberation.

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  • Acoustic Detection and Detectors

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