Applicable Condition of the Approximate Parameter Estimation Method of the Generalized Gamma Distribution

The generalized Gamma distribution (
$\text{G}\Gamma \text{D}$
) has been found accurate for modeling synthetic aperture radar (SAR) data. To facilitate the practical applications of this model, an approximate method for estimating the parameters in the
$\text{G}\Gamma \text{D}$
was recently given by Stacy (1962) and discussed by Krylov et al. (2013) and Abramowitz and Stegun (1972), in which the applicable condition of the method is restrictive and incorrect. This article further derives the analytical condition of the applicability of the method. Examples of theoretical analysis and simulations verify the correctness of the derivations.