Microwave scattering by rough polyhedral particles on a surface

TL;DR

This study uses numerical simulations to analyze microwave scattering by rough polyhedral particles on surfaces, highlighting how particle shape, size distribution, and permittivity influence backscattering and polarimetric properties relevant to remote sensing.

Contribution

It provides a detailed numerical analysis of how particle shape, size distribution, and permittivity affect microwave scattering, with implications for remote sensing of planetary surfaces.

Findings

Particle roundness and size distribution significantly affect polarimetric scattering.

Permittivity has a minor role within the studied parameter range.

Circular polarization ratio is robust against size and SFD variations.

Abstract

The electromagnetic (EM) scattering by non-symmetric wavelength-scale particles on a planar surface has numerous applications in the remote sensing of planetary bodies, both in planetary and geo-sciences. We conduct numerical simulations of EM scattering by rough polyhedral particles (with 12 or 20 faces) using the discrete-dipole approximation and contrast the results to that of spheres. The particles have permittivities corresponding to common minerals in the microwave regime ($\epsilon_r=4.7 + 0.016$i and $7.8 + 0.09$i), and a size-frequency distribution (SFD) consistent with the observed scattering properties (power-law distribution of size parameters between 0.5 and 8 with an index from $-2.5$ to $-3.5$). The assumed substrate permittivity $2.4 + 0.012$i corresponds to a powdered regolith. We present what roles the particle roundness, permittivity, and SFD for a realistic range of parameters play in the EM scattering properties as a function of incidence angle with a focus on backscattering in microwave-remote-sensing applications. The particle roundness and SFD have a clearly observable effect on the polarimetric properties, while the role of permittivity is relatively minor (in the studied range). Among various backscattering observables, the circular polarization ratio is the least sensitive to the decrease of the upper boundary (down to a size parameter of 3) and the index of the SFD.