Rotation estimation for two-dimensional forward-looking sonar mosaicing

Abstract

Two-dimensional forward-looking sonars are becoming standard sensors in both remotely operated and autonomous underwater vehicles, increasing the possibility of mapping under low visibility conditions. Due to the inherent nature of sonar image formation, the ideal mapping strategy relies on maintaining the same orientation, so as to minimize intensity alterations due to viewpoint changes. However, this is not always possible and therefore it is necessary to deal with the registration of sonar images under rotational movements. Previous investigations have discouraged the use of feature-based techniques and have suggested the use of global methods that are robust to noise, low-resolution and inhomogeneous insonification and can deal with the decoupled estimation of roto-translations. In this paper we review several candidate methods and assess them by using real data gathered under different conditions. By identifying the best approach for rotation estimation we aim to extend the applicability of sonar mosaicing to more diverse scenarios. Results indicate that applying phase correlation directly to polar frames leads to the highest accuracy under most cases.