A preliminary study of shallow-water sonar issues : signal motion loss and reverberation noise
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This preliminary investigation addresses key program elements for sonar sensing in a shallow-water environment to establish bounds on possible solutions and to reduce program uncertainty. The modeling and experimental program focuses on two issues - the potential degradation of sonar data due to signal masking by shallow-water reverberation and signal loss caused by extreme platform motions. The research program combines theoretical analysis, experimental validation in a shallow-water environment, and development of a computer model to explore parametric sensitivity. Results from an initial dock-side test show good agreement with the theoretical predictions. From the shallow-water experiments and acoustic modeling we conclude that: (1) Signal motion loss can influence the reverberation level significantly but is not the dominant factor in target detection for sonars in the frequency range of interest (>200 kHz); a high-quality (velocity-aided) inertial navigation and attitude system will be sufficient to correct for geometric distortions caused by platform motion. (2) Although surface reverberation and multipath noise can be a factor, partcularly in shadow-mode imaging, reverberation levels are rapidly attenuated at the frequencies of interest and beam patterns can be manipulated to reject most interferences; echo-mode imaging is still dominated by the contrast between target strength and bottom reverberation.
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