Subsurface Radar Sounder On-board EnVision Mission to Venus

Abstract:

EnVision, one of the three candidates for ESA’s Cosmic Vision 2015-2025 M5 medium-class missions, aims to explore the present-day activity, the geological history of the surface and the hostile climate of Venus. It will carry on-board the Subsurface Radar Sounder (SRS), an orbital ground-penetrating radar, aimed at searching for subsurface structures and address crucial science questions on the evolution of Venus surface. In addition to subsurface exploration, SRS will also provide surface altimetry measurements.

The geological targets supporting the scientific objectives of SRS are: 1) buried and modified impact craters, to determine the nature and thickness of the impact infilling, 2) stratified units, to understand their stratigraphic relationships, 3) tessera highlands, to investigate their 3D geomorphology and potential buried structures, 4) plains, to estimate their dielectric properties, 5) lava flows/fields, to estimate their roughness, dielectric properties and range of thickness for constraining their modes of emplacement.

SRS design and operation strategy is based on maximizing the performance in terms of penetration capability, and range and along-track resolutions constrained by the challenges in the acquisition process, i.e. target dielectric properties, surface topography, and propagation through the ionosphere. Based on extensive simulations and performance assessment, the current baseline is defined at a central frequency of 9 MHz with a bandwidth of 5 MHz, thereby allowing penetration of a few hundreds of meters through the crust with a range resolution around ~20 m depending on the target. Considering the ionosphere, the acquisitions are preferred on the night-side and are planned in two modes: (1) high density with track spacing of 10 km, covering about 20% of the planet, and (2) low density with track spacing of 50 km and lossy compression, covering 80% of the surface. Further studies are in progress to simulate the SRS radar response to the expected acquisition conditions.