Speckle noise reduction in the mapping of submarine linear structures in synthetic aperture sonar images
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Abstract
The use of the Synthetic Aperture Sonar (SAS) in the hydrographic survey with autonomous underwater vehicle (AUV) has enabled the mapping of small objects at great depths. The SAS images from these surveys are of high resolution due to synthetic aperture technology and the AUV approach to the target of interest. Despite these advantages SAS image are highly corrupted by a granular multiplicative noise, called speckle noise, which hamper automated object identification methods. The objective of this paper was to evaluate quantitatively and qualitatively the reduction of speckle noise, as well as the increase in the contrast of features of underwater linear structures, pipelines and cables, associated to oil and gas transport in synthetic aperture sonar images using techniques image enhancement. Two images acquired by High Resolution Interferometric Synthetic Aperture Sonar (HISAS) 1030 were used, with spatial resolution of 4x4 cm and radiometric resolution of 8 bits. From the results, it was verified that the speckle noise had a significant reduction of 14.4% and 6.9%, and a discrete gain of 0.2% and 1.2% for each image, respectively, in the enhancement of features the study areas. The results showed that the use of image enhancement functions is a powerful tool in reducing speckle noise and improving the definition of objects of interest in SAS images, thus allowing faster and more efficient semiautomatic processing of feature extraction.
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