Review on Ultrasonic Techniques for Underwater Object Classification

ABSTRACT: Underwater object classification is an attractive approach using acoustic remote sensing techniques due to its high coverage capabilities and limited costs as compared to manual method of taking samples from the seafloor. This review paper focuses on the characterization of underwater objects in a coastal environment using different ultrasonic techniques like multibeam echosounder (MBES), a single-beam echosounder (SBES) and sidescan sonar(SSS). Out of these ultrasonic techniques, MBES and SBES are, in general, high-frequency techniques providing information about bathymetry and backscatter for the upper part of the sea bottom. MBES systems provide this information with a better resolution due to the beam opening angle of typically 1 -3 , and high coverage. An SBES provides measurements directly underneath the ship only, but is widespread. For MBES underwater object classification is achieved through the Bayesian approach, employing backscatter measurements per beam. For the SBES, echo shape parameters of the transmitted signal are determined and are combined in a principal component analysis (PCA). Underwater object classification using these ultrasonic techniques is useful for a large range of applications, such as habitat mapping, cable laying, or mine hunting. KEYWORDS: Underwater object classification, single-beam echosounder (SBES), multi-beam echosounder (MBES), backscatter measurement, sidescan sonar(SSS) I.INTRODUCTION The knowledge of oceanic environment is found to be necessary for many applications, such as coastal engineering, marine geology and marine biology [1]. Also, the environment needs to be known accurately when evaluating the acoustic propagation characteristics in shallow-water environments, e.g., for sonar performance assessment. Hence this motivates us for gathering of information about properties of the water column, under water objects that is the watersediment interface and the deeper sediment layers. The classical technique applied for gathering of information for underwater objects is based on taking samples of the sediment but these techniques are very costly, time consuming and doesn't give enough information as measurements are taken at point positions only. Hence this review paper is dedicated to methods allowed for underwater sediment classification using ultrasonic techniques such as multibeam echosounders (MBESs), e.g., [2]-[4]; single-beam echosounders (SBESs), e.g., [5]-[7]; and sidescan sonars (SSSs), e.g.