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Auto-focus for circular synthetic aperture sonar

A method of focusing fully-coherent circular synthetic aperture sonar (CSAS) imagery is provided. A k-space representation of the CSAS image is generated using the two dimensional Fast-Fourier Transform (FFT). Sub-aperture images are generated by windowing the k-space representation and applying the two dimensional inverse FFT to the windowed spectrum. All adjacent complex sub-aperture images are correlated, the correlation peaks are detected and the relative shifts in X and Y as a function of look-angle are recorded. The relative shifts between adjacent sub-apertures are integrated and the means are subtracted to find the absolute shift as a function of look-angle. A motion-solution is calculated by exploiting the relationship between apparent scene shift and actual vehicle sway. The motion estimation is used to generate a phase-correction matrix that is multiplied by the k-space representation of the fully-coherent image.

Timothy M. Marston

Patent Number: 
Patent Issue Date: 
February 20, 2015
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