Keypoint-based mapping analysis on transformed Side Scan Sonar images
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Keypoint-based mapping analysis on transformed Side Scan Sonar images M. Dhana Lakshmi 1 & S. Sakthivel Murugan 1 Received: 31 March 2019 / Revised: 25 May 2020 / Accepted: 24 June 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
In recent years, detecting wrecks and submerged sites is a challenging task and timeconsuming. A fine technique is required to pick out features from the sea-floor. Side Scan Sonar (SSS) has been used for underwater imaging to detect submerged objects on the seafloor. Due to the rotational and translational instabilities of SSS tow-fish, the acquired SSS images may be distorted. Hence, this paper concentrates on the geometric transformation analysis for different shadows of SSS images. Based on the intensity-based threshold method, the SSS images are classified as high-shadows, low-shadows, no-shadows, and semi-shadows. Different keypoint detector and mapping algorithms are considered for the extraction of keypoints (features) and matching of those detected points. The point mapping performance was evaluated using Repeatability rate and Mapping rate. It is observed that the Mapping rate of 98.7% is obtained using Scale Invariant Feature Transform (SIFT) with Fast Library for Approximate Nearest Neighbor Search (FLANN) and RANdom Sample Consensus (RANSAC). It is also inferred that the Repeatability rate is 0.8 using Oriented FAST & Rotated BRIEF (ORB) compared with other algorithms considered. Keywords Keypoint detection . Point mapping . Repeatability rate . Mapping rate
1 Introduction Most of the ocean world’s features are being discovered, and imaged by their interactions with sound. Acoustic sensors (sonars) are the common consideration in underwater exploration [16]. Side Scan Sonar is one of those which uses the pulse of sound shot sub-horizontally across the sea bottom
* S. Sakthivel Murugan [email protected] M. Dhana Lakshmi [email protected]
1
Underwater Acoustic Research Laboratory, Department of Electronics and Communication Engineering, SSN College of Engineering, Kalavakkam, Chennai, Tamilnadu 603110, India
Multimedia Tools and Applications
from a towed transducer or tow-fish and images the ocean floor [18]. These obtained images are in the form of the monochrome image, consisting of a single color against a neutral background and each pixel is stored as a single bit (0 or 1). These sonars sound pulses reflect off object that project above the bottom [27]. The strength and travel time of reflected pulses are recorded and processed into an image, it works even in murky or black water. Hard areas such as rocks on the sea-floor reflect sound fast and have a stronger return signal than softer areas with sand. Additionally, objects or features that rise above the sea-floor cast shadows in the sonar image where no acoustic signal hits [19]. Several applications of SSS are Mine warfare, Hydrography survey Geological survey, Search and recovery, Locating Pipelines, drowning Victim and aircraft search, underwater archaeology, classif
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