The deep sea exploration and exploitation is one of the biggest challenges of the next century. Military, oil & gas, offshore wind farming, underwater mining, oceanography are some of the actors interested in this field. The engineering and technical challenges to perform any tasks underwater are great but the most crucial element in any underwater systems has to be the sensors. In air numerous sensor systems have been developed: optic cameras, laser scanner or radar systems. Unfortunately electro magnetic waves propagate poorly in water, therefore acoustic sensors are a much preferred tool then optical ones. This thesis is dedicated to the study of the present and the future of acoustic sensors for detection, identification or survey. We will explore several sonar configurations and designs and their corresponding models for target scattering. We will show that object echoes can contain essential information concerning its structure and/or composition.

Sonar systems for object recognition

The uniform geometrical theory of diffraction (UTD)-type analysis of electromagnetic (EM) scattering from an array of periodic structures is presented, whose solutions were developed by an extension from the analogous 2-D EM scattering problem. The array is semi-infinite along one of its two dimensions. The scattering fields are interpreted by the diffraction mechanisms of the UTD framework including the reflection, transmission, and truncation diffractions. This technique is particularly useful to analyze the EM properties of frequency-selective surfaces and metamaterials composed of periodic structures with identical elements by an integration of full-wave numerical techniques to analyze the array elements. Thus, it may treat a relatively flexible elemental structure and makes the solution very useful in practical applications. Numerical examples are presented to demonstrate the applicability of these solutions.

An UTD-Analysis of Electromagnetic Scattering From Periodic Array Structures With a Straight Truncation Boundary

This paper presents the asymptotic formulation of ray fields in the decomposition of electromagnetic (EM) scattering mechanisms from a one-dimensional, semi-infinite and periodic array when it is illuminated by a line source. This technique can be applied to analyze the passive FSS (frequency selective surface) type periodic structures with identical elements, or the reflectarray and transmitarray type antennas that are phased to radiate EM fields focused in the near zone of the array aperture. The solutions are built up based on the Floquet mode expansion of the scattering fields, and are obtained by asymptotically evaluating the resulted integrals to express the fields in terms of reflected/transmitted and edge diffracted fields as previously addressed in the framework of uniform geometrical theory of diffraction (UTD). The theoretical investigations over the scattering mechanisms and propagation phenomena are performed. Numerical examinations are presented to demonstrate the utilization of these solutions.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015RS005669

V. P. Yakubov

Papers

Kirchhoff's approximation method of geometrical optics in the problem of scattering of waves at an irregular surface