Using Shadows in Circular Synthetic Aperture Sonar Imaging for Target Analysis
Circular synthetic aperture sonar (CSAS) enhances azimuth resolution and coverage but sacrifices seafloor shadow information—critical for target recognition and 3D reconstruction—due to its omnidirectional imaging. This work presents the first systematic approach to recover and exploit shadows from CSAS data: multi-view images are generated via sub-aperture filtering, clear shadows are extracted using a fixed-focus shadow enhancement (FFSE) technique, and an interactive visualization interface facilitates manual segmentation. Subsequently, a space-carving method infers the 3D shape of targets from shadow contours. By moving beyond the conventional reliance on intensity-only CSAS imagery, the proposed framework significantly improves target identification and demonstrates the efficacy and potential of shadow information for underwater 3D reconstruction.