Sequential focus evaluation of synthetic aperture sonar images

A synthetic aperture sonar (SAS) system borne by an autonomous underwater vehicle is state-of-the-art for highresolution sea floor mapping. In the application of automatic target recognition, e.g., for naval mine hunting, the high-resolution SAS images serve as input to a detection and classification post-processing stage, which highly relies on excellent image quality. Future autonomous mine hunting systems must include an assessment scheme to ensure sufficient quality for performing target recognition. We propose to assess the focusing capability during the reconstruction of an SAS image to evaluate its quality by probing the instantaneous cross-range resolution of a synthetic sub-aperture and comparing it with its theoretical resolution.