Near- and far-field simulations of coherent backscattering from scatterers in finite sized aggregations

Abstract

Classification of scatterers is a difficult but important step in active sonar applications. Active sonar signals in an ocean environment are scattered by surface roughness, and volume inhomogeneities in the bottom and water column. Fish schools may be important water-column clutter sources and, under some circumstances, may preferentially backscatter sound because of acoustic coherent backscattering enhancement (CBE). Here, the addition of in-phase scattered waves from propagation path pairs can readily explain a scattered intensity enhancement of a factor of two in the direction opposite to that of the incident wave. This presentation describes CBE simulations for finite sized aggregations of point scatterers using the Foldy (1945) equations that show much larger enhancements are possible in the far-field of the scattering aggregation. The simulations are validated in the near field with the theory from Akkermans et al. (1986), and with existing CBE optics and acoustics experiments from Wolf and Maret (1985) and Aubry et al. (2007). The dependence of the width of the CBE backscattered peak in the far-field is reported. Extension of these results to sonar pulse scattering from schools of fish is also very briefly discussed. [Work supported by the Office of Naval Research.]