Analysis of Surface Clutter for Subsurface Radar Sounding on Venus

ESA's EnVision mission has been selected for Venus exploration, with launch scheduled in 2031. It will carryon-board the Subsurface Radar Sounder (SRS) to profile the shallow crust at low frequency and support the understanding of Venus' geological history. In the design and performance assessment of SRS, an important step is the analysis of off-nadir clutter due to rough surface scattering and its potential to mask the scientifically relevant subsurface echoes. While there have been studies to understand the roughness of Venusian terrains from data available from the previous missions, there are few studies that analyze the roughness and clutter at the wavelength-scale of a low-frequency radar sounder instrument. In this paper, we present a first step towards filling this gap by analyzing the clutter performance of selected sites on Venus where subsurface interfaces are expected, namely the plains, the impact craters, and the lava flows. Using surface roughness parameters and fractal modelling, we generate multiple surface realizations, simulate the SRS clutter response and analyze the probability distribution of clutter depth and power. The results show that for most of the sites, clutter is concentrated very close to the surface, and therefore does not significantly affect the subsurface detection.