A model-experiment validation of near-range phase center breakdown

Spatial coherence of a scattered field has helped to improve sensor navigation techniques and field imagery. Under the phase center approximation (PCA), a bistatic sensor geometry is approximated as a monostatic phase center. In the far field, the approximation is valid, and signals with common phase centers are highly coherent. The approximation fails when a non-trivial spatiotemporal delay appears in the sensor’s near-field, and signals that share phase centers are less coherent. A model by Brown and Blanford shows this near-field degradation of PCA, using comparisons between the van Cittert-Zernike Theorem and a point-based scattering model. Experimental validation of the model was performed using an in-air sonar mounted on a linear actuator. The sonar collected returns from a shallow bed filled with plastic beads, which approximates rough interfaces typical of underwater environments. Multiple trials were conducted using a variety of transmitters, receiver placements, and ping intervals. These geometries were simulated using the point-based scattering model and the two sets of data were compared in order to validate the model. Results from this model-data comparison, along with future applications for sonar imaging and navigation, will be discussed.