Extraction of 3-Dimensional Features by Analyzing Underwater Images obtained from SONAR fitted on Autonomous Underwater Vehicle (AUV)

Abstract

With the advent of Imaging SONAR, the field of underwater imaging has been gaining lot of importance especially for Autonomous Underwater Vehicle (AUV) for obstacle avoidance.AUV is the underwater robot used for detecting the underwater mines, monitoring and surveillance of coastline and important dense traffic movement ports and other vital defence installations. The AUV applications include the obstacle trajectory tracking, obstacle avoidance and intelligence surveillance and reconnaissance(IRS).The heart of the AUV system depends on the performance of the SONAR. SONAR provides the navigation and guidance by mounting it on the AUV and operates on the principle of acoustic wave propagation. SONAR provides only the location of the object in terms of range and bearing and the objects dimensions (length and thickness) but not the obstacle depth information. For effective maneuvering and for analyzing the target features especially for collision avoidance, the depth information of the object in 3Dimensions is important. In order to know the depth of the obstacle using 2D SONAR, the 2-Dimensional images of the obstacle at different elevation angles are obtained and are used to reconstruct the 3D. This is achieved by scanning the object at various depths. There can be two conditions one in which the SONAR beam partially covers the object, and the second in which SONAR beam covers the complete object. The algorithms developed for this analysis of SONAR data demonstrate the usefulness of the proposed system in the process of converting 2D to 3D information. In this paper a method along with the algorithm that has been designed and developed to calculate the aspect of the target in 3 Dimensions from the 2 Dimension images received from the imaging SONAR by scanning the objects at the various depths is presented. It has been concluded that by using the proposed method and by implementing the proposed algorithm in the 2D SONAR, the high precision 3D aspect of objects has been achieved. The main advantages of proposed algorithm are cost saving and high precision of reconstructed objects.