“…While several analytical backscattering models exist, the focus of this review will be the discussion and evolution of the Integral Equation Model (IEM) which was introduced in 1992 and has been subsequently revised to improve the representativeness and validity range of the model (Fung et al, , 1994Mattia and Le Toan, 1999;Hsieh et al, 1997;Chen et al, 2000Chen et al, , 2003Wu et al, 2001;Liu et al, 2003;Fung and Chen, 2004). Focus is placed on the IEM because other analytical models such as the Geometric Optics Model (GOM) (Ulaby et al, 1982) and Small Perturbation Method (SPM) (Ulaby et al, 1982) are approximated by the IEM at high and low frequencies respectively, leading to the conclusion that these are special cases of the IEM Fung, 1994), and because it is by far the most widely used theoretical model found in the literature over the last decades.…”