A broadband, bistatic model for the spatial coherence of diffuse scattering

Spatial coherence describes the similarity of two spatially-separated observations of a signal. It is a property that finds use in many applications but is of particular importance within the field of active sonar. The van Cittert-Zernike theorem (vCZT) is a well-known optical model describing the spatial coherence of a radiated field that has been previously applied to acoustic problems, including coherence-based micronavigation. The limiting assumptions of the vCZT hold for some active sonar applications but are not valid for classes of sonar systems that operate in bistatic geometries with a wide transmit bandwidth. To address this gap in the existing work, this paper describes the development of a spatial coherence model for rough interface scattering in broadband, bistatic applications. The proposed model builds on many of the same foundational principals as the vCZT but removes monostatic assumptions and allows frequency-dependent parameters to be applied across a wide bandwidth. The broadband, bistatic model is experimentally validated with an in-air scattering experiment. Finally, limitations of the model are discussed and potential extensions of this work are presented.