Sediment roughness characteristics measured by broadband spectral analysis of acoustic echoes

Abstract

Acoustic signals scattered from the sea floor at nearly vertical incidence contain information about the physical properties of the sea floor. Signals may be decomposed into spatially coherent and spatially incoherent components the relative magnitudes of which are primarily a function of small scale bottom roughness. Experimental interping coherence functions derived on the basis of a linear system scattering model are shown to characterize contrasting sediment lithologies. The use of interping coherence as a sediment remote classification criterion and hence as a tracer of gross geotechnical properties is explored.

Remote acoustic classification of marine sediments with application to offshore Newfoundland

“…We discuss the implementation of an automated sediment classification-of data collected in the outer Placentia Bay area of offshore Newfoundland, extending work reported by Dunsiger and Cochrane (1981) and Dunsiger et al (1981~).…”

“…The inter-ping coherence or y function as discussed by Dunsiger and Cochrane (1981) and Dunsiger et al (1981~) is defined as:…”

“…When internal layering is indistinct Q4, becomes highly erratic and unpredictable as the two cross-spectra approach random fluctuation noise levels. Dunsiger and Cochrane (1981). An approximate gravel designation has been added.…”

“…Shells are numerous on photographs of Placentia Bay soft-sediment surfaces. There is evidence that shells are responsible for patches of high scatter (apparently surface scatter with highly complex arrivals) in Sable Island sands (Parrott et al 1980;Dunsiger et al 1981~). Scattering from shells deposited on or embedded in soft sediments could be considerable but the effect is not easily delineated with the ground truth available.…”

“…The former is primarily a frequencydependent measure of combined surface and volume scattering (Dunsiger and Cochrane 198 1;Dunsiger et al 1981~); and latter is a frequency-dependent measure of the character of internal layering of a sediment. The work is a follow-up to that of Dunsiger and Maclsaac Can.…”