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Studies on the Technology of Passive Time-Reversing Location

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Tutor: NiMing
School: National University of Defense Science and Technology
Course: Underwater Acoustics
Keywords: time-reversing,vertical linear array,horizontal linear array,dismatch of environ
CLC: TN911.7
Type: Master's thesis
Year:  2010
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Abstract:
In order to overcome the difficulties in the signal processing of underwater acoustic caused by the multiple paths effect, the performance of the passive time-reversing location in the shallow ocean is researched in this paper. The performances of time reversal focusing of vertical linear array and horizontal linear array in the shallow ocean are studied, the main contents are as follows.1. The changes of the vertical linear array¡¯s passive location performances with the aperture, the number of the sensors and the frequency band of the source wave are studied. Through the simulation analysis using the computer, it comes the conclusion that a vertical linear array has good passive detection performance if it has huge aperture, enough receiving sensors and uses a width frequency band signal as the source wave.2. Through the computer simulation, it comes the conclusion that the horizontal linear array fixed on the bottom of the sea needs more huge aperture to realize effective passive time-reversing location in the same sea areas. A combined horizontal linear array composed with three single ones is introduced to minish the range of dead angle effectively.3. The performances of the detection of the vertical linear array in noise environment are analyzed. The performance of the vertical linear array¡¯s detection under noise environment can be improved effectively through augmenting the aperture and increasing the number of sensors. Then the influences to the performance of the horizontal linear array¡¯s detection caused by the dismatch of the environment are discussed and the performance to detect more than one target of a horizontal linear array with huge aperture is studied.4. In order to gain the ocean acoustic parameters of the actual ocean areas, the method for inverse algorithms to gain ocean bottom parameter based on single floor sea bottom model is introduced. The sensitivity to the aim function of every parameter has been analyzed, and it will minish the calculational amount and improve the efficiency by grouping inverse algorithms based on the different sensitivity.5. In the process of the ocean experimental data, it realizes exact target location by using the time-reversing method to process the exploded sound and linear frequency modulation wave. It proves that the method of time-reversing processing is feasible in the actual application.
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