Numerical modelling of multiple scattering between two elastical particles

Abstract

-Multiple acoustical signal interactions with sediment particles in the vicinity of the seabed may significantly change the course of sediment concentration profiles determined by inversion from acoustical backscattering measurements. The scattering properties of high concentrations of sediments in suspension have been studied extensively since Foldy's formulation of his theory for isotropic scattering by randomly distributed scatterers. However, a number of important problems related to multiple scattering are still far from finding their solutions. A particular, but still unsolved, problem is the question of particle proximity thresholds for influence of multiple scattering in terms of particle properties like volume fraction, average distance between particles or other related parameters. A few available experimental data indicate a significance of multiple scattering in suspensions where the concentration is higher than 20 g/I of sand particles. This paper reports an attempt to illuminate and to solve the proximity threshold question, by an in-depth numerical study of the interaction of ultrasonic signals with two canonically shaped elastical particles. Introductory experimental results seem to create evidence for the applicability of this new numerical model.

Interference of Echo-Signals from Two Buried Spherical Targets

“…The form-function for two spherical scatterers of the same radius a is naturally defined as (see [6]),…”

“…The simplest realistic problem of multiple scattering by finite bodies appears to be that by two spheres. Many publications on this subject can be found in [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. However, an important case of buried scatterers has not been studied in these papers.…”

“…In [6] it is shown that in the case of two spherical scatterers in water it is possible to neglect the multiple scattering between scatterers if d > 8a. When targets are buried in the attenuating bottom, the condition d > 8a is more than sufficient to neglect the multiple scattering between spheres.…”