Adaptive frequency filtering for forward-looking sonar imagery spectral registration

In the last few years, forward-looking sonar devices have emerged as a powerful perception alternative for those underwater environments with reduced visibility. Thanks to its capability to deliver high quality acoustic images at a near-video frame rate, they can be regarded as the analogous tool of optical cameras for operations conducted in turbid waters. However, despite the analogy, the particularities of forward-looking sonar imagery pose a significant challenge to the techniques typically used on optical images and, especially, to the key step of image registration, essential in applications like mosaicing, sonar-aided navigation or image denoising. In this sense, previous investigations have encouraged the use of spectral registration methods as a promising alternative over the traditional feature-based registration approaches used on optical images. In this paper, we propose to improve the spectral registration of forward-looking sonar images with an adaptive filtering technique that allows to cope with the noise and variability inherent to the forward-looking sonar image registration problem. Results show that by using the proposed filtering we achieve a more accurate pairwise alignment of the sonar images that can benefit subsequent processing in many applications.