High frequency propagation and scattering from water saturated granular sediments: laboratory study
Résumé
Sound backscattering and reflection from water-saturated granular sediments at frequencies from 150 kHz to 8 MHz at normal and oblique incidence was studied in controlled laboratory conditions. Two kinds of natural sediments, well sorted medium and coarse sands and two comprised with glass beads of corresponding grain size, were taken for the study, degassed, and their surface was flattened. At oblique incidence, intrinsic scattering due to the sediment granular structure can be considered as a dominating mechanism of backscatter. Comparison of frequency dependencies of the backscattering strength for sediments with different mean grain size shows the existence of a scaling effect that allows a description of the backscattering strength as a scaling function of one parameter, the mean grain size/wavelength ratio. Comparisons with previous results obtained for moderately sorted sands shows effects of the grain size distribution width. Comparisons for sand and glass beads of the same size demonstrate effects of the grain shape. Possible applications to remote sensing of marine sediments, and particularly determining the sediment mean grain size, are discussed. [Work supported by ONR and CNRS].