Acoustic, Electromagnetic and Optical Sensing and Monitoring Methods: Principles of Acoustic and Electromagnetic Sensing

Due to capabilities of transmission in underground, a brief introduction on underground measurement methods by adopting kinds of "wave" (including field wave, acoustic wave, and electromagnetic wave) is presented. Among them, acoustical measurement methods are the most widely used in practical applications. Hence, some typical acoustical measurement methods are introduced with more details, from their principles to application examples. Electrical and electromagnetic methods are also widely adopted and more traditional methods in geological exploration and subsurface structure detection are described. Several routine approaches and their applications are exhibited, too. While, in practical applications, how to sense the "waves" in rugged measurement environment is another important issue. Due to the presence of many extra benefits in "waves" sensing compared to traditional methods, optical sensing techniques are summarized and introduced with their application examples.Ground penetrating radar (GPR) is a nondestructive evaluation (NDE) technology for detecting, locating, and inspecting objects or structures buried underneath ground surface. It is also applicable to detect objects behind walls or other dielectric barriers. In this chapter, the operating mechanism of GPR is explained. Moreover, the GPR circuit design, signal processing, and applications are presented.