Abstract:

Acoustical and bathymetric data were collected near the Mid-Atlantic Ridge as part of the Acoustical Reverberation Special Research Program (ARSRP) in 1993. The wideband time-domain envelope statistics of backscatter from prominent bathymetric features exhibit a non-Rayleigh character which previous researchers have described as event-like. The envelope probability density functions (pdf's) show enhanced tails at high levels which can be a source of active sonar clutter. It is proposed that the origin of such clutter is single-scale, nonfractal roughness. High-resolution bathymetry reveals a power spectral density (PSD) with power-law form. Wavelet analyses reveal a single-scale character to the roughness. In order to test the hypothesis, multiscale and single-scale realizations of the measured PSDs are used in numerical simulations of time-domain backscatter. At the range and azimuthal resolutions in the experiment, the envelope pdfs for multiscale surfaces are Rayleigh, while the single-scale surfaces lead to enhanced tails as observed in the data. The conclusions drawn are that along with an interface's rms height, correlation length, and power spectral shape, one should also be concerned with its scale structure because it plays an important role in the physics of wave interaction at random interfaces.