Three-dimensional numerical modeling of refraction and reflection scattering from icy galilean satellites

Abstract

Radar scattering from the icy galilean satellites is marked by unusually high backscatter cross sections and polarization ratios at wavelengths λ 0=3.5–70 cm. The persistence of exotic scattering behavior over this large a wavelength range suggests that the responsible mechanisms remain at least partially effective as the wavelength approaches or exceeds the size of individual scatterers. We examine two models previously analyzed in the geometrical optics limit—radar glory from buried craters (Eshleman, 1986, Science 234, 587–590) and refraction scattering from subsurface lenses (Hagfors et al., 1985, Nature 315, 637–640)—at wavelength scales using three-dimensional finite-difference time-domain (FDTD) numerical simulations. We include craters with rough walls and lenses with random inclusions of heterogeneous material. For hemispherical craters spanning up to 3 λ 0 in diameter, we observe none of the exotic backscatter behavior attributed to the geometrical optics models. Nonspherical refraction scatterers can produce circular polarization ratios μ C>1 and linear polarization ratios μ L=0.5–0.8 at diameters as small as ∼ λ 0, but the density of such inclusions must be high if refraction scattering alone is to account for the measured cross sections.