ASA 125th Meeting Ottawa 1993 May

5aSA4. Time-frequency domain processing of acoustic echoes from elastic shells in water.

G. C. Gaunaurd

Naval Surface Warfare Ctr., White Oak Detachment R-14), Silver Spring, MD 20903-5000

H. C. Strifors

National Defense Research Establishment, Sundbyberg, Sweden

Acoustic echoes have been studied from submerged elastic shells in either the frequency or the time domains in a number of earlier works. They are now studied and processed in the combined time-frequency (t-f) domain, using both idealized and realistic incident pulses. In a first analysis, (Gaussian) time-windowed Fourier transforms are used, and later, pseudo-Wigner distributions (PWD) are used, and applied to the cases of both ideal and realistic incident pulses. These echo processing techniques extract in various ways the time evolution of the resonances that the target in question may contain within the chosen (broad) operational band. Suitable choice of viewing windows and carrier frequencies serves to generate (t-f) domain displays in which clearly recognizable resonance features become evident. These can then be linked to particular target characteristics. The adjustable widths of the time windows control the amount of detail in the displays. The resulting three-dimensional plots will be shown in an informative colorized format for various cases dealing with elastic shells in water. This will illustrate the target-ID or target characterization merits of this approach, over those obtainable from the usual (monostatic) sonar cross sections.