By Paolo Franchi In Memorandum Reports
High-resolution, multi-chromatic, multi-view and resonance synthetic aperture sonar imaging. Xenaki, Angeliki; Pailhas, Yan; Dugelay, Samantha. CMRE-MR-2019-024. June 2020.
Synthetic aperture sonar (SAS) provides high-resolution acoustic imaging by coherently processing the backscattered acoustic signal recorded over consecutive pings. Traditionally, object detection and classification tasks rely on high-resolution seafloor mapping achieved with wide-beam, broadband SAS systems. However, frequency or aspect-specific information is crucial for improving the performance of automatic target recognition algorithms. For example, low frequencies can be partly transmitted through objects or penetrate the seafloor providing information about internal structure and buried objects, while multiple views provide information about the object's shape and dimensions. Sub-band and limited-view processing, though, degrades the SAS resolution. To overcome the resolution limitation in multi-chromatic and multiview imaging, we formulate SAS imaging as an l 1-norm regularized least-squares optimization problem, which improves the resolution by promoting a parsimonious representation of the data. The optimization problem is solved in a distributed and computationally efficient way with an algorithm based on the alternating direction method of multipliers. The resulting SAS image is the consensus outcome of collaborative filtering of the data from each ping. The potential of the proposed method for high-resolution, narrowband and limited-aspect SAS imaging is demonstrated with simulated and experimental data.