Acoustical Imaging of Extended Targets by means of Synthetic Aperture Sonar Technique

Performance evaluation of synthetic aperture systems providing high resolution sea bottom images is often achieved by means of point target responses' analysis. This paper proposes a more complete approach including the backscattering properties of complex environments made up of rigid extended targets laid down on rough seabeds. This means that both deterministic target echoes and random bottom are taken into account. The two-dimensional time-space response of the synthetic array is introduced to provide a representation of the image as the spatial convolution of this transfer function and the complex distribution of scatterers modelling the scene. Images of spheres and cylinders laid down on a seabed are studied through both numerical and experimental approaches which are compared and validated. Both results show the ability of extracting the target shadow from bottom reverberation thanks to the synthetic aperture. This technique can be used for target detection as well as for target identification but studies of the feasibility of such imaging systems should take into account the statistical behaviour of echoes.