Improvements to Automated Change Detection Tools for SAS Images

The process of reviewing seabed survey imagery for defence applications is time consuming for naval operators, and this workload is expected to increase with the large data volumes generated as high resolution synthetic aperture sonar (SAS) comes into service. Change detection is a means of reliably detecting newly occurring, moved, or removed seabed objects. It is particularly effective in cluttered environments such as harbours, or in areas that are routinely surveyed. While this technique offers a robust solution to the workload problem, in-service operator tools for post-mission analysis of survey imagery that are specifically designed for change detection are lacking. Coherent change detection (CCD), operating on complex-valued SAS imagery, offers the possibility of detecting very subtle seabed changes, and is an area of current research interest that is not yet implemented in operational tools. Automated change detection (ACD) processing performed on-board the sonar platform during the survey will provide the largest operational utility.Recognizing the complementary aspects of the three nations’ naval research programs in this area, the US (NSWC-PCD, ARL Penn State), Canada (DRDC), and Norway (FFI) have formed a collaborative project to advance operator aids for change detection: Coalition Underwater Mine and IED Defeat (CUMID). Goals of the joint program are to: improve robustness of image-based ACD algorithms; draft requirements and specifications for ACD performance assessment, including both evaluation of past or ongoing performance and prediction of future performance; and architect operator displays, tools, and decision aids. The envisioned final output of the collaboration is a set of well-crafted requirements and recommendations that can be implemented in a manner fitting national priorities and capabilities.This paper provides an overview of current change detection practice (the state of the art), the coalition project, activities ongoing in the participating nations’ research programs, highlights of workshop outputs, and plans for the future.