Radarclinometry at Venus: first results and validation strategies

Abstract

Motivation: The past few years have seen a renewed interest in Venus, with multiple missions planned for the early 2030s. Currently, the main source of topographic information at Venus is from the SAR onboard Magellan, which in its altimetric mode measured the time delay of radar pulses reflected off the Venusian surface to determine the distance to the spacecraft. The radar altimeter provided data for 98% of Venus’ surface at a resolution of 10-20 km horizontally and a vertical precision of about 30 meters. A smaller fraction of the planet was also imaged sufficiently to allow stereo reconstruction. These maps have been fundamental in advancing our understanding of Venusian geology and they continue to be a critical resource for planetary scientists. However, their large footprint prevents the detailed study of smaller, narrow Venusian structures with this dataset. Increasing the horizontal resolution of current profiles by a factor 50-100 over the global maps would help understand the physical properties of Venusian lava and the variety of phenomena leading to dome emplacement. It would also tighten constraints on the modeling of the lithospheric flexure typically associated with moats, depression, and fractures observed between domes or coronae and their neighboring planes. Methods: Based on a technique analogous to photoclinometry with optical images, radarclinometry can retrieve elevation from SAR images by relating the intensity of radar backscattering to the slope, roughness, and dielectric constant of the surface. Crucially, the Magellan SAR instrument also collected radar backscatter (brightness) images with a resolution of ~100 m/pix. Even after stacking several (radar) images in a trade-off between horizontal and vertical resolution (to reduce the noise related to the speckle noise in the image), recovered elevation profiles may still support a much higher resolution than global SAR altimetry, and thus more detailed geologic and geomorphologic analyses.Results and outlook: We present preliminary results of our effort to extend terrain reconstruction capabilities of bodies with dense atmospheres using the radarclinometry technique. We validate our implementation by: 1- Processing Magellan observations of surface features for which high resolution elevation profiles are available from past studies; 2- Closed-loop simulations of synthetic Magellan data based on the most recent information about Venus' surface; 3- Applying our implementation to available radar measurements of terrestrial sites, where highly resolved ground truth is available. Future work will focus on providing the community with a modern implementation of radarclinometry and on producing “SAR-resolution” elevation profiles for a set of critical features to advance our understanding of tectonic processes on the planet, and to lay the groundwork for future missions and studies.