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Abstract: The towing operation mode of side-scan sonar system (SSS) easily results in dislocations and distortions of targets in the SSS strip image, brings difficulty to the mosaic of these strip images by the geocoding method or the tessellation-line method and affects the recognition and understanding for seabed relief. Therefore this study proposes a new method, namely the segment-image mosaic method based on corresponding features of the two adjacent SSS strip images. Through SSS image preprocessing, segment match based on corresponding features and image fusion in the common coverage area based on wavelet transformation, this new method overcomes the drawbacks of the traditional methods of image mosaic, fulfils well the mosaic of SSS strip images and finally a whole-area SSS image is formed. Experiments have verified that the mosaic image formed by the new method can correctly reflect the position, shape and distribution of seabed targets, which is helpful to understand seabed relief.
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1 Introduction
Side-scan sonar system (SSS), as a conventional seabed survey equipment, is mainly used for acquiring high-resolution sonar images of seabed relief, which can intuitively reflect the position, type, shape, size and other attributes of the seabed objects. To weaken the influence of the hull noise on SSS images, the towfish, namely the transducer of SSS, is often towed behind the survey ship in actual SSS measurement. Under the towing operation mode, the factors like ship attitude, waves, currents and hull manipulation may result in inaccurate towfish position estimated by ship position and cable length, and then cause inaccurate location of the SSS image [1]. Moreover, marine reverberation, fish school, suspended solids and other disturbances are likely to bring about noise to the sonar image, some of which may result in misjudgment for the seabed features [2]. Besides, influenced by vessel speed, vessel heading, sound speed in the water, incident angle of acoustic beam, seabed gradient and other factors, the SSS image often has different degree deformations and dislocations along and across the track line [3, 4]. All these factors result in low-quality image in the mosaic of adjacent SSS strip images (see Fig. 1).
In the mosaic of sonar images, the traditional methods, such as the tessellation-line method and the geocoding method, are...