Characterization of the Complex Permittivity of Planetary Regolith Analogue Materials

Radar has long been used as a tool for remote sensing of planetary bodies. Orbital radar systems are or have been in orbit around the Moon, Mars, and Venus, while ground-penetrating radar systems are or have been used on the Moon. Despite an abundance of radar data, a lack of information on the fundamental electromagnetic properties of the surface and near-subsurface materials of these bodies precludes detailed quantitative analysis. This includes determining the precise depth of radar-detected sub-surface features as well as refining estimates of abundance of subsurface materials, such as the mineral ilmenite. Although laboratory measurements have been made in the past in order to quantify electromagnetic properties of lunar and martian materials, these measurements provide a limited view of the parameter space of influence on these electromagnetic properties. This thesis develops a full methodology to measure the complex permittivity of planetary regolith analogue materials in vacuum over a broad range of frequencies. These methods are first demonstrated with measurements of analogue regolith materials appropriate for carbonaceous asteroids: individual and mixed components of a regolith simulant based on CI meteorite mineralogy. These measurements are the first to investigate the effect of carbonaceous material on the complex permittivity of asteroid regolith analogues and they provide new constraints on the attenuation of radar in granular carbonaceous materials. This thesis also develops a Bayesian Markov Chain Monto Carlo (MCMC) -based parameter estimation technique to determine the frequency-dependent complex electric permittivity and magnetic permeability. The technique uses a generalized dielectric response (GDR) model to simultaneously determine the complex permittivity and permeability from measured scattering parameters. The technique is able to accurately determine both of these electromagnetic parameters for low-loss, high-loss, and magnetic materials. Finally, measurements of samples with systematically varying amounts of ilmenite are presented along with Bayesian model fits using a one-pole Cole-Cole model. These results represent the first systematic laboratory measurements investigating the effect of ilmenite on radar attenuation. They demonstrate the significant frequency-dependent effect of ilmenite content on signal attenuation and show promise for the application of dielectric spectroscopy, or the identification of materials based on the physical parameters of a GDR model.Ph.D