Deconvolution of low-frequency ocean sediment acoustic signals. I. Simulation study

Abstract

The previous paper described a Fast Field Program propagation model consisting of two contiguous, semi-infinite, constant sound-speed fluids (ocean and sediment). A point source and a receiver were placed in the ocean above the boundary and varied in range to simulate a (real world) relative type bottom loss measurement. A 100-msec, 50-Hz sinusoidal pulse was transmitted through the ocean to study the reflected and lateral acoustic wave interaction at the boundary. To obtain the acoustic impulse response of the simulated sediment, deconvolution was performed by dividing the spectrum of the sediment interacting acoustic signal by the spectrum of a transmitted (direct path) signal and computing the inverse Fast Fourier Transform. Controlled amounts of Gaussian noise were added to simulate ambient noise. Even low noise levels (S/N=20 dB) were found to degrade the process to a point where the deconvoled signal was no longer discernable. The degree of degradation was determined by comparing bottom reflectivity ratios and lateral and reflected waveforms, after deconvolution, obtained in the absence and presence of noise. Applying averaging and stabilization techniques reduced noise degradation significantly. A 16-mm motion picture camera is requested to show a 5-min film of the modeling results. [This work was sponsored by Naval Sea Systems Command, SEA 06H1-4, A.P. Franceschetti.]