T. T. Hsu
L. Carin
Dept. of Elec. Eng., Polytechnic Univ., Six Metrotech Center, Brooklyn, NY 11201
L. B. Felsen
Boston Univ., Boston, MA 02215
A finite difference time-domain (FDTD) code has been used to assemble a comprehensive data base of realizations for short-pulse plane wave scattering by a fluid shell model target submerged in the presence of a randomly distorted bottom interface. The entire problem is two dimensional with the scattered acoustic pressure observed along an elevated track above the target and parallel to the mean bottom boundary. Two bottom topographies are examined: (1) a smoothly deformed interface between the wated column and a fluid bottom; (2) a collection of soft randomly pitched thin flat strips. The database furnished by the ensemble of realizations for the randomly irregular bottom, in which the deterministic target remains unchanged, is subjected to wave-oriented data processing that yields space-wave number and time-frequency phase space distributions extracted via windowed transforms and refined by locally applied high resolution algorithms. The processing is applied to the target alone, the cluster alone, and the target--clutter combination. Target resonances are regarded as a major discriminant which one needs to enhance by input signal shaping and output filtering while simultaneously de-emphasizing the corrupting effect of the clutter. Statistical measures pertaining to the clutter are given consideration, as is the effect of system noise added to the data. Results are presented and discussed. [Work supported by ONR and AFOSR.]