Scattering from inclusions in Marine Sediments: SAX04 Data/Model Comparisons

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Service, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188) Washington, DC 20503. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) 08-14-2008 REPORT TYPE Final Technical DATES COVERED (From -To AUTHOR(S)Ivakin, Anatoliy N. 5f. WORK UNIT NUMBER PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Applied SPONSOR/MONITOR'S ACRONYM(S)APL-UW SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)Office of Naval Research 875 North Randolph St. Arlington, VA 22203-1995 SPONSORING/MONITORING AGENCY REPORT NUMBER DISTRIBUTION AVAILABILITY STATEMENTApproved for public release; distribution is unlimited SUPPLEMENTARY NOTES ABSTRACTThe role of discrete scatterers in marine sediments is evaluated based on acoustic and environmental measurements at the shallow water sediment acoustics experiment, SAX04, and shown to be significant. The sediment at SAX04 site was complicated and characterized as a mostly medium sand / mud mixture. Analysis of the sediment samples showed presence of a small volume portion of arger particles, such as coarse sand fraction and shell fragments, which were considered as inclusions, or sparsely distributed discrete scatterers, embedded in a homogeneous effective fluid with parameters corresponding to medium sand or mud sediment frame. This analysis provided also the size distributions for both types of inclusions, coarse sand particles and shells, which were used as inputs to a model of incoherent discrete scattering in the sediment. It is demonstrated that this approach in general is capable to provide a reasonable explanation of both frequency and angular dependencies of the SAX04 bottom backscattering strength, and discrete scattering from the sediment inclusions can be a significant mechanism of the SAX04 high frequency reverberation in a wide range of grazing angles (15 to 50 degrees) and frequencies (30 kHz to 500 kHz). SUBJECT TERMSbackscattering strength, medium sand and mud sediments, shell fragments, coarse sand inclusions, particle size distribution Abstract-The role of discrete scatterers in marine sediments is evaluated based on acoustic and environmental measurements at the shallow water sediment acoustics experiment, SAX04, and shown to be significant. The sediment at SAX04 site was complicated and characterized as a mostly medium sand / mud mixture. Analysis of the sediment samples showed presence of a small volume portion of larger particles, such as coarse sand fract...

Acoustic Backscattering From a Sand and a Sand/Mud Environment: Experiments and Data/Model Comparisons

“…For SAX04, the volume scattering models predict (and the data below 130 kHz confirm) a nearly constant scattering level as frequency increases but the data indicate a much sharper increase above 200 kHz. Ivakin's results [1] demonstrate that scattering from shells is a viable candidate for explaining the data above 200 kHz.…”

“…(Modeling of the higher frequency data is presented in [1]). The model to be used treats sand sediment as a fluid but with a density determined by using the effective density fluid model (EDFM) [10].…”

“…4(d)] can be developed along the lines of the volume scattering model presented in [11] and [16]. The backscattering cross section is given by the expression [compare to (1)…”

“…In a previous examination of these data [3], scattering from discrete scatterers (e.g., shells and shell fragments) was proposed as one mechanism, which is not included in the type of model used, to explain this behavior. This possibility is explored further in [1] and will be discussed again below when examining data from the full range of frequencies used in SAX99 and SAX04. Second, the model correctly predicts the increase in overall backscattering level as a function of frequency.…”

“…In [1], the possibility that scattering from discrete scatterers is responsible for backscattering is examined. As part of that effort the experimental results shown in Fig.…”