Processing of forward scattered acoustic fields with intensity sensors

In bistatic scattering geometries, the detection of a signal scattered in the forward direction by a stationary object can be difficult because the incident and scattered waves combine into a simultaneous mixture. Reverberation can complicate the measurements even further. At opposite ends of the forward scattering phenomenon are the Rayleigh scattering region, where the scattered wave is masked by the incident wave; and the geometrical optics region, where the two wavefields interfere to form an acoustic shadow. Pressure sensors can only provide an estimate of the magnitude of the intensity associated with an equivalent plane wave field, while true intensity sensors measure simultaneously the acoustic pressure and particle velocity components (or a related quantity such as acceleration, displacement, or pressure gradient) at a single "point" in space. The coherent measurement of both acoustic field parameters provides not only the magnitude of acoustic intensity but the phase between acoustic pressure and velocity. It is hypothesized that processing methods could be developed which exploit the relationship between these types of coherent measurements in order to extract information regarding the presence and nature of an object residing on or very close to the bistatic baseline. In this paper, this hypothesis is explored computationally using a rigid prolate spheroid as a canonical scattering body.