Advanced Methods for the Simulation of Radar Sounder Planetary Data

Radar Sounder (RS) are active remote sensing instruments operating at low frequencies with a nadir-looking geometry, capable of penetrating the surface to investigate the subsurface of planetary targets. The data acquired by these systems are the result of complex interactions between instrument parameters, the acquisition geometry and the properties of the investigated celestial body. Consequently, simulation tools play a fundamental role throughout the entire life-cycle of a mission with a RS instrument as a payload. In the design phase, they provide a virtual environment to optimize system parameters and assess trade-offs between different configurations of the instrument parameters to fulfill its scientific requirements. In the scientific phase, they are essential for both forward modeling, validating geological hypotheses against synthetic data, and inverse modeling, where they support the retrieval of geophysical properties from complex observational data. Despite this pivotal role, the current landscape of simulation methodologies is constrained by a fundamental dichotomy between computational efficiency and physical fidelity. On the one hand, rigorous numerical simulation methods offer the high accuracy required for modeling complex small-scale scattering interactions but incur in prohibitive computational costs for mission-scale analysis. On the other hand, ray-tracing simulation methods provide the necessary efficiency but often rely on approximations that fail to capture complex wave interactions. This limitation is further compounded by the emergence of next-generation concepts for RS with distributed and polarimetric architectures, which introduce multistatic geometries that existing simulation tools cannot adequately model. This thesis addresses these challenges by developing novel simulation frameworks that bridge the gap between computational feasibility and accuracy. The research presents three primary contributions to support the design and interpretation of current and future RS missions. First, a dictionary-based hybrid simulation method is proposed to efficiently model multi-scale scattering phenomena. This approach integrates the large-scale efficiency of a ray-tracing simulation method with the high accuracy of a rigorous numerical method. By injecting a pre-computed dictionary of small-scale scattering responses and transmission losses into the simulation loop, the framework captures realistic surface and subsurface roughness effects without the computational burden typically associated with full-wave solvers. Second, the thesis establishes a multi-layer simulation framework for RS in distributed architecture configurations. This methodology extends state-of-art ray-tracing simulation modeling capabilities to support multi-platform formation-flying configurations. By incorporating full polarimetric scattering matrices and a reformulated Stratton-Chu integral, the framework enables the coherent synthesis of large aperture responses and facilitates the assessment of advanced clutter suppression techniques, such as Direction-Of-Arrival (DOA) estimation. Third, a simulation-based evaluation framework is presented to quantify the impact of environmental factors on geophysical retrieval. Focusing on the hostile radio environment of the Jovian system, this study integrates forward modeling with an inverse approach utilizing a statistical reflectometry technique. This closed-loop strategy quantifies the degradation of signal quality caused by surface roughness and planetary noise, establishing robust operational thresholds for the reliable retrieval of surface characteristics. Collectively, these contributions enhance the state-of-art by providing a generalized set of tools that merge physical accuracy with computational efficiency. The proposed solutions not only address the existing modeling limitations but also establish a methodological framework that could support performance analysis for new RS concepts and ensure robust data interpretation for the next generation of RS, for both planetary exploration and Earth observation.