Maritime surveillance using a wideband hydrophone
Wilson, Jason K.
Rice, Joseph A.
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Undersea acoustic modems acquire wideband acoustic time series through an electro-acoustic transducer and use on-board digital signal processing for receiving acoustic communications. These component devices can potentially serve a dual use for passive sensing of radiated acoustic energy from maritime vessels. This thesis examines the characteristic Lloyd's mirror interference pattern present in the acoustic spectrogram of a passing surface target and applies two-path ray theory and waveguide invariant theory to an analysis of the phenomenon. The two theories are shown to be mathematically equivalent under certain conditions. In combination with the Doppler shift from a target tonal, these theories permit a calculation of target range and speed at the closest point of approach (CPA). Such analysis is applied to spectrograms obtained in a controlled experiment at the approaches to San Diego Bay. For targets passing within 185 meters of the receiver, the resulting Lloyd's mirror pattern permits calculation of the range to within 9%. Target speed obtained from the Doppler shift is within 4% of the ground truth value.
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