The Jet Propulsion Laboratory’s S-band Synthetic Aperture Radar (VenSAR) selected by NASA is currently undergoing scientific, technical and mission assessment. A SAR is a versatile remote sensing technology that has unique capabilities for determining geophysical information often not available by other remote sensing methods. VenSAR will characterise structural, and geomorphic evidence of multi-scale processes that shaped the geological history of Venus as well as characterise current volcanic, tectonic, and sedimentary activity.
VenSAR will provide several imaging and ranging techniques from a polar orbit: (1) regional and targeted surface mapping, (2) global topography and altimetry, (3) stereo imaging, (4) surface radiometry and scatterometry, (5) surface polarimetry, (6) repeat pass interferometry opportunities.
Regional and targeted surface mapping
VenSAR will obtain SAR imagery at 30 m (resp. 9 m) resolution, at targets of regions of up to 1000 x 1000 km (resp. 100 x 100 km).
Radar stereo or radargrammetry uses image displacements or parallax measurements between radar images acquired at different incidence angles to solve for topography. Unlike radar interferometry, radar stereo does not use phase information, and in fact is usually applied in imaging geometries that exceed the critical baseline precluding standard interferometric techniques. The large swath employed by the VenSAR instrument creates useful stereo imaging geometries that can be used to measure Venus’ topography.
Because the interaction of an electromagnetic wave with a surface can be polarisation dependent, this can be exploited to infer information about an object or scene being observed. VenSAR will measure HH + HV SAR polarimetry, enabling global mapping of polarimetrically resolved microwave radiometry.
When analyzed in synergy with polarimetry active measurements, off-nadir radiometry can be used to determine the surface effective temperature and therefore (1) search for thermal anomalies; (2) investigate variations of the temperature with altitude where topography is available; (3) investigate variations of the temperature with time (e.g., due to varying local hours oron-going volcanic activity) if repeated observations are planned.