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Experimental analysis of the effects of bistatic target scattering on synthetic aperture sonar imagery

Downward looking synthetic aperture sonar (SAS) systems, such as those used to detect surficial and buried unexploded ordinance, may use arrays with large spatial extent compared to the depth of the targets they are imaging. With such systems the targets are in the near field of the physical array formed by the projector and receiver. Beamforming algorithms, data representation schemes, and automated target recognition algorithms can benefit from considering the bistatic scattering patterns of targets in this geometry. In downward looking SAS systems, resonant scattering behavior may be used to discriminate targets from clutter because scattering from the sediment-water interface may obscure the geometric scattering response of targets. An experimental analysis of the effects on SAS imagery due to bistatic collection geometries was conducted using an in-air laboratory setup with resonant targets. This data was used to develop a signal processing algorithm that may help improve target localization, detection, and identification by focusing re-radiated resonant energy from targets. Results from the application of this algorithm are compared for an approximately monostatic and a truly bistatic SAS collection geometry using an aluminum pipe target.