Radiative transfer and multiple scattering of diffuse ultrasound

Radiative transfer and multiple scattering of diffuse ultrasound" (1994). Faculty Publications from the Department of Engineering Mechanics. Paper 6. A model is presented for the mtltiply scattered incoherent field in a continuous polycrystalline elastic medium. Unlike a previous, development based upon energy conservation considerations [J.] for a medium containing discrete random scatterers, the pt(sent model has been developed from the wave equation and first principles. Appropriate ensemble averaging of the wave equation leads to Dyson and Bethe-Salpeter equations which govern the mean Green's function and the covariance of the Green's function, respectively. These equations are expanded for weak heterogeneity and equations of radiative transfer are obtained. TIt e result is valid for attenuations that are small compared with a wave number: odk • l. Polarization effects are included, as before, through five elastodynamic Stokes parameters, one longitudinal and four shear. The theory is applied to a statistically homogeneous and statistically iso topic half-space composed of cubic crystallites illuminated by a plane wave. Results for the ang • lar dependence of backscattered intensity are presented. It is anticipated that this approach mzy be applicable to microstructural characterization through the study of the time, space, ultrasonic frequency, and angular dependence of multiply scattered ultrasound in elastic media.