Accession Number : ADA291088

Title :   Theoretical Estimates of High Frequency Acoustic Attenuation and Backscattering from Suspended Sand Particles in the Ocean and in an Estuary,

Corporate Author : DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION CANBERRA (AUSTRALIA)

Personal Author(s) : Thuraisingham, R. A.

PDF Url : ADA291088

Report Date : NOV 1994

Pagination or Media Count : 25

Abstract : Theoretical estimates of high frequency sound attenuation and backscattering strengths from suspended sand particles in the ocean and in an estuary are given. The estimates are obtained using the measured volume concentrations of suspended particle in the upper layers of the ocean, from the particle size spectra near the clear water minimum, and from measurements of suspended sediments at different depths from the bottom of an estuary. Estimates are given for frequencies in the 1-10 MHz region. Contributions to acoustic attenuation from scattering, viscous drag and thermal conduction are evaluated separately using existing theoretical models. Contribution to attenuation from thermal conduction is negligible at the frequencies used. For particles in the sub micrometer to 10 um range attenuation is predominantly due to viscous drag. For large particles scattering is the main cause of attenuation. Estimates reveal attenuation and backscattering near the bottom of the estuary is quite high. At 5 MHz, attenuation at a depth of 80 cm and 10 cm from the bottom are approximately 0.1 dB/m and 10 dB/m respectively. At this frequency backscattering strength at 80 cm and 10 cm depths from the bottom, are approximately - 25 dB and -5dB respectively. (AN)

Descriptors :   *BACKSCATTERING, *ACOUSTIC ATTENUATION, *OCEAN MODELS, HIGH FREQUENCY, OCEAN SURFACE, PARTICLE SIZE, SAND, ESTIMATES, PARTICLE SPECTRA, SUSPENDED SEDIMENTS, THERMAL CONDUCTIVITY, ACOUSTIC SCATTERING, MIXED LAYER(MARINE), DRAG, VISCOSITY, UNDERWATER ACOUSTICS, OCEAN BOTTOM, DISPERSIONS, SOUND RANGING, ESTUARIES.

Subject Categories : Physical and Dynamic Oceanography
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE