4pUW4. Conjugate mirror array performance in the presence of surface and bottom roughness.

Session: Thursday Afternoon, May 16

Time: 2:20

Author: Terry E. Ewart
Author: Daniel Rouseff
Author: Darrell Jackson
Location: Appl. Phys. Lab. and School of Oceanogr., Univ. of Washington, Seattle, WA 98105


Dowling and Jackson [J. Acoust. Soc. Am. 91, 3257--3277 (1992)] provided a study of the temporal/spatial effects of an internal wave field on phase conjugate arrays. In the present work the effects of interface roughness on phase conjugate arrays are simulated. The stochastic surface wave field is generated to include realizations of the sea surface height that evolve in time. The time variability of the surface also includes the effects of the acoustic travel time, so that each realization is ``as viewed'' in the frame of the acoustic wave from source-array-to-receiving-array and the return after phase conjugation., The acoustic wave propagation is accomplished using a parabolic equation marching algorithm that includes this random rough surface. Bottom penetration and absorption are included. Coupling of the surface wave field with the bottom/sub-bottom randomness can produce an increased degradation of the return field. Thus even if the processing time to produce the conjugate field approached zero, degradation of the conjugate array focus will occur. A discussion of the relevance of this work to conjugate array applications will be presented. [Work supported by ONR.]

from ASA 131st Meeting, Indianapolis, May 1996