A re‐examination of the IEM model for microwave scattering from randomly rough boundary

Advances in soil moisture retrieval from synthetic aperture radar and hydrological applications

“…1) and the transition between the use of the incident and specular angle as surface roughness increases (Wu et al, 2001). The resulting model is termed the Advanced Integral Equation Model (AIEM) (Fung and Chen, 2004;Liu et al, 2003;Wu and Chen, 2004). A summary of the diverse versions of the IEM with various complexities and a focus on model users can be found in Fung and Chen (2010) and a summary of the above advances for the IEM and other models can be found in Table 3.…”

“…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.…”

“…Integral Equation Model (IEM) Fung et al (1992) -Initial derivation of IEM theoretical backscattering model Fung (1994) -Separated IEM into simple and complex forms for single and multiple scattering Hsieh et al (1997) -Removed simplification of Green's function Mattia and Le Toan (1999) and Zribi et al (2000) -Introduced fractal ACF Chen et al (2000) -Derived upward and downward scattering complimentary field coefficients -Improved multiple scattering Wu et al (2001) -Derived transition function between Fresnel and specular angles Liu et al (2003) -Incorporated transition function and updated Green's function to derive AIEM Fung and Chen (2004) -Incorporated transition function into original IEM Wu and Chen (2004) -Incorporated transition function and updated Green's function to derive AIEM Oh Model (OM) Oh et al (1992) -Initial development of semi-empirical Oh model Oh et al (1994) -Incidence angle function added -Surface autocorrelation function added Oh et al (2002) -Incidence angle function updated Oh (2004) -Correlation length removed due to insensitivity of model to surface slope Dubois Model (SEM) Dubois et al (1995a,b) -Initial development of Dubois semi-empirical model Sahebi and Angles (2010) -Updated coefficients to increase site specific model accuracy in agricultural fields, the backscattered signal is the sum of the vegetation and soil contributions, and has soil moisture information incorporated into it making retrieval of soil moisture possible (Joseph et al, 2010;Mattia et al, 2003b). In order to separate the influence of vegetation and soil on radar signal, it is necessary to determine vegetation parameters for inclusion into models.…”