Radar albedos and circular-polarization ratios for realistic inhomogeneous media using the discrete-dipole approximation

- Computations of electromagnetic scattering by inhomogeneous particles are presented.
- The effect of the chemical and structural composition of the inhomogeneity is shown.
- Scattering applications are envisaged in the planetary radar research.

Electromagnetic scattering is simulated using the discrete-dipole approximation for inhomogeneous spheres and closely-packed aggregates of spherical particles with an emphasis on backscattering and planetary radar applications. The simulations are utilized to study how different parameters, including the composition and distribution of a homogeneous medium, affect the circular-polarization ratio and the radar albedo. Two different pairs of refractive indices are chosen, using values relevant for asteroids and meteorites of silicaceous and basaltic materials at microwave wavelengths. The results show substantial variance due to the geometry at backscattering, which is why analytic formulae cannot be deduced. However, some tendencies are visible: for example, the circular-polarization ratio increases when the structure becomes less isotropic as well as when the effective refractive index increases due to an increase in the phase shift. As for the radar albedo, the values computed for the homogeneous spheres with an equal effective refractive index correlate to some extent, but also differ from the radar albedos of the inhomogeneous spheres systematically. For the aggregates of spheres, the effect of the general shape and differences between the algorithms that dominate the effects caused by the inhomogenization. We find that the general scattering features remain regardless of the inhomogeneous internal structure.