Surface Change Detection at Venus: The Requirements and Potential from Earth Analog Studies

The forthcoming Venus missions (EnVision, VERITAS and Venus Orbiter Mission) pro-vide the opportunity to detect inter-mission changes in Synthetic Aperture Radar (SAR) imagery across a 40-year time gap since Magellan, and intra-mission changes within the periods of the new missions. Achieving reliable inter-mission change detection will not be straight forward, however, since the radar instruments have differing viewing geometries, wavelengths and spatial resolutions, and we therefore need to consider carefully how best to undertake such efforts.

Repeated high-resolution radar imaging with consistent viewing geometry will allow direct comparison of features, to pick up morphological and backscatter patterns associated with physical and potentially com-positional surface changes. Such comparison demands precise image co-registration and reliable image feature matching, and these rely on topographic data of comparable resolution to ensure that geometric and terrain distortions in SAR imagery are removed. Also needed are robust methods to identify and extract real feature changes in an effective, automated way, for repeatability and to save time.

There is growing indirect evidence of recent volcanic activity on Venus but to fully understand the likely character of surface changes, the use of analog sites and Earth Observation data is needed. To characterize the full variety of geomorphologic feature-type changes we might expect (volcanic, tectonic, erosional, depositional, impact etc.), cases are needed where change is occurring at suitable spatial and temporal scales and where plentiful repeated images exist in archive. Hence we are using freely available global Senti-nel-1 (and other) SAR data at a series of sites to develop automated change detection approaches.