Video Enhancement for Underwater Exploration Using Forward Looking Sonar

The advances in robotics and imaging technologies have brought various imaging devices to the field of the unmanned exploration of new environments. Forward looking sonar is one of the newly emerging imaging methods employed in the exploration of underwater environments. While the video sequences produced by forward looking sonar systems are characterized by low signal-to-noise ratio, low resolution and limited range of sight, it is expected that video enhancement techniques will facilitate the interpretation of the video sequences. Since the video enhancement techniques for forward looking sonar video sequences are applicable to most of the forward looking sonar sequences, the development of such techniques is more crucial than developing techniques for optical camera video enhancement, where only specially produced video sequences can benefit the techniques. In this paper, we introduce a procedure to enhance forward looking sonar video sequences via incorporating the knowledge of the target object obtained in previously observed frames. The proposed procedure includes inter-frame registration, linearization of image intensity, and maximum a posteriori fusion of images in the video sequence. The performance of this procedure is verified by enhancing video sequences of Dual-frequency Identification Sonar (DIDSON), the market leading forward looking sonar system.