Dominant-plus-Rayleigh Models for RCS: Swerling III/IV versus Rician

A Swerling III/IV target is generally thought of as the sum of a dominant nonfluctuating reflector plus many smaller scatterers, and the many smaller scatterers are often thought of as having a combined voltage amplitude that is Rayleigh distributed (i.e., Swerling I/II). On the other hand, a Rician target is the result of a complex sum at baseband of a nonfluctuating object and a Rayleigh object. The Rician model is not easily reconciled with the standard four degree of freedom χ² distribution for the (power) amplitude of a Swerling III/IV target, and, indeed, we show here that no Swerling III/IV target is Rician. However, when the nonfluctuating or “dominant” part of the Rician target is approximately 75% of the total reflection, their dissimilarity is minimized (and is small). This phenomenon holds true when Gaussian receiver noise is involved.