This book describes the processes of radio propagation and analyzes the equations that enable estimation of media -- It explores propagation processes and related phenomena including absorption, refraction, reflection, and scattering -- It also analyzes how knowledge of radiowave properties allows accurate estimations of media via inverse problems -- The authors examine the empirical methods that interpret remote sensing data and how they are applied in the creation of useful approximation models, and discuss the operational principles of microwave devices used in remote sensing, and provide insight into the stabilizing a priori information that greatly increases the accuracy of remote sensing solutions.