Stochastic features of scattering

Abstract

The characteristics of scattering of scalar waves in stochastic random media are investigated in through the behaviour of the meanfield, scattering attenuation, and transmission fluctuations of amplitude and phase. Coherent scattered waves develop with increase of perturbation level, with the strength of the coherency varying with the type of media. The frequency content of the coherent scattered waves is close to that of the incident waves, and the phase is dependent on the statistical effect of the heterogeneities along the propagation path. The normalized scattering attenuation (Qs-1/ ε2) is stable at low normalized wavenumbers (ka < 1) regardless of the perturbation strength, but varies with the perturbation strength at high normalized wavenumbers (ka > 1). The coherent scattered waves, which strengthen with the perturbation level, add energy to the primary waves and reduce the apparent scattering attenuation. Stable measurements of normalized scattering attenuation can be made for sufficiently large distances. An empirical distance criterion for such stable measurements of scattering attenuation is presented in terms of propagation distance, incident wavelength, and the correlation length of the heterogeneities in the medium. The transmission fluctuation of amplitude and phase shows a high variation at large spatial lags, and the trend of the variation is dependent on the nature of heterogeneities. The ensemble average of amplitude fluctuation closely follows the theoretical prediction, but rather poor agreement is displayed for phase fluctuation. The effect of self-averaging during propagation in random media can not replace the ensemble averaging for mean transmission fluctuations of the amplitude and phase in random media.