Coherent backscattering of acoustic waves in the near field

Recent studies have shown that interference plays an important role in vari ous phenomena observed for waves propagating through random media. Among th ese phenomena, the so-called cone of coherent backscattering has received m uch attention in optics. In this paper, we study analytically and numerical ly the coherent backscattering of acoustic waves in a seismological context . Tn particular, we focus on the near-field detection of scattered waves an d the effect of transient sources. We show that interference results in an increase of the coda intensity as compared to the prediction of radiative t ransfer theory. After a transient regime, a spot of backscattering enhancem ent stabilizes in a sphere of radius half a wavelength centred at the sourc e of seismic waves. Several effects such as absorption, boundary conditions and scattering anisotropy are investigated. Our study demonstrates the rob ustness of coherent backscattering and may offer a possible means of discri minating single versus multiple scattering in the observed coda.