Aineto, Manuel M. (1998) Adaptive filtering of reverberation for active sonar signal detection. PhD thesis, University of Warwick.

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Abstract

The extremely high absorption of energy of electromagnetic waves in underwater environments restricts the range of signals to be used to acoustic signals. In addition the sea is a complex medium in which many kinds of environmental changes, mul­tipath propagation phenomenon, masking of the signals of interest by noise and/or reverberation signals, and attenuation, among others, will affect the propagation of sound through it.
On one hand, environmental changes will cause different degrees of nonstationarity at the signals to be processed. On the other hand, the use of acoustic waves will imply that, for the active sonar case, different Doppler shifts of the signals to track will take place as the relative radial velocity of the sonar platform to the contact varies. This will cause that in some instances the contact signals share not only time, but also frequency bins with the noise and/or the reverberation signals. For the noise-limited case, an optimum solution for signal detection based on the correlation receiver or Matched-filter, exists. However, for reverberation-limited environments there is not any optimum solution which is feasible to be implemented in a practical system. Adaptive filters grew out of the demand of systems capable of operating in uncertain, time-varying environments. Due to the wide range of applications for which they have shown to be useful, considerable amount of work has been dedicated during the last few years to their development. The preliminary part of the thesis presents a basic model of the underwater environment for the active sonar case upon which the suitability of certain adaptive structures for active echo detection and rang­ing is initially based. A classification and the description of some existing adaptive systems and their main characteristics are presented too. Subsequent parts of the thesis include the theoretical development of a generic adaptive algorithm which will operate with complex data sequences. Several sets of experiments are carried out and the results presented in order to investigate the suitability for the application of interest of several adaptive systems and algorithms. Adaptive processing the received signals as presented here must be understood as a preprocessing stage of the overall active sound navigation and ranging (sonar) problem. The study is restricted to the narrowband case.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Signal processing -- Digital techniques, Sonar, Electromagnetic waves, Wave guides, Underwater acoustics, Acoustical engineering
Official Date:	August 1998
Dates:	Date Event August 1998 Submitted
Institution:	University of Warwick
Theses Department:	Department of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Lawson, Stuart,1946-
Sponsors:	Defence Evaluation and Research Agency
Extent:	xvi, 228 leaves : illustrations
Language:	eng

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