An Overview of Wavefields
A sensor array is used to measure wavefi elds and extract information about the sources and the medium through which the wavefi eld propagates. It is therefore imperative that some background in different types of wavefi elds and the basic equations governing the wavefi eld must be acquired for complete understanding of the principles of array signal processing (ASP). In an idealistic environment of open space, homogeneous medium and high frequency (where ray approach is valid), a thorough understanding of the wave phenomenon may not be necessary (those who are lucky enough to work in such an idealistic environment may skip this chapter). But in a bounded inhomogeneous medium and at low frequencies where diffraction phenomenon is dominating, the physics of the waves plays a signifi cant role in ASP algorithms. In this chapter, our aim is essentially to provide the basics of the physics of the waves, which will enable us to understand the complexities of the ASP problems in a more realistic situation. The subject of wave physics is vast and, naturally, no attempt is made to cover all its complexities.