Accession Number : AD0856029

Title :   The Effect of Periodic Bottom Layering on Acoustic Reflectivity.

Descriptive Note : Technical rept.,

Corporate Author : SACLANT ASW RESEARCH CENTRE LA SPEZIA (ITALY)

Personal Author(s) : Hastrup, Ole F.

Report Date : 01 JUL 1969

Pagination or Media Count : 33

Abstract : An inspection of a large number of cores taken in the Atlantic and Mediterranean shows that deep sea sediments are frequently deposited by turbidity currents, thereby causing alternate layers of clay and sand that in many cases are vertically distributed in a periodic way. It is shown that such a periodicity in the layers causes bands with low reflection losses in the frequency domain where the thickness of a combined clay-sand layer equals half the acoustic wavelength. This effect has been demonstrated by experimental data obtained from bottom reflection measurements in the Tyrrhenian abyssal plain near Naples. The periodicity of a composite clay-sand layer has been computed by Fourier transforms of the sediment density curves. The frequency obtained in this way, corresponding to the half-wavelength criterion, agrees very well with the low-loss frequency band determined from the experimental reflection-loss frequency curves.

Descriptors :   (*UNDERWATER SOUND SIGNALS, REFLECTIVITY), (*OCEAN BOTTOM TOPOGRAPHY, UNDERWATER SOUND SIGNALS), (*OCEAN BOTTOM SAMPLING, SEDIMENTATION), SONAR SOUND ANALYZERS, SEDIMENTARY ROCK, CLAY, SAND, OCEAN CURRENTS, ACOUSTIC PROPERTIES, DENSITY, SOUND TRANSMISSION, UNDERWATER SOUND, ATLANTIC OCEAN, ANTISUBMARINE WARFARE, ECHO RANGING, MEDITERRANEAN SEA, REVERBERATION, OCEAN BOTTOM, SONAR SIGNALS, REFLECTION.

Subject Categories : Physical and Dynamic Oceanography
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE