EnVision/VenSAR

Science modes

VenSAR is based on the NovaSAR-S instrument built for the UK Space Agency and launched in 2018. NovaSAR-S SAR Payload developed by Airbus Defence and Space is an active antenna is configured from an array of 18 identical phase centres each comprising a 2 × 2 array of dual polar, 6-element sub-arrays, designed for low-cost Earth Observations and operating at 3.2 GHz (9.4 cm) in the S-band, ideal for the Venus atmosphere. VenSAR adapts this modular design by taking 24 of these phase centres and configuring them into a six columns of four rows, producing a 5.47 × 0.60 m active phased array antenna capable of delivering five key science modes: InSAR (VI1 as standard, VI2 for orbit-to-orbit, and VI3 for opposite-look), stereo polarimetry (VP1 StereoPolSAR), all at Reconnaissance scale (30 m resolution); Exploration scale imagery (VH1 HiRes at 6 m resolution); Locality-scale Sliding Spotlight (VS1 Spotlight at 1 m resolution); and Zonal-scale microwave brightness temperature (VR1 Radiometry).


This figure illustrates the VenSAR mapping sequence for the ~16 orbits in every 24 hours: 4 orbits are reserved for telemetry (open circles); 3 pairs of orbits for InSAR (VI1 and either VI2 or VI3); 2 orbits for StereoPolSAR; and 4 orbits for HiRes and Spotlight. 

Polarimetry

EnVision’s InSAR radar instrument is sensitive primarily to the morphology (roughness and slope) and relative permittivity of the surface materials. Polarimetric data provide important information about the nature of the surface and near subsurface that cannot be obtained solely with backscatter power images, such as those obtained by Magellan. In particular, polarisation ratios can help identify the thickness and grainsize of loose surface sediment. Since terrestrial studies show that almost all natural targets have reciprocal cross polarisation (i.e. HV backscatter is identical with VH), only HH, VV, and VH (or HV) polarisations are required to characterise the backscatter properties.

Differential InSAR


VenSAR SAR payload Front End (3 views) ans a signal New Instrument Architecture (NIA) Back End generated from NovaSAR CAD models.

Differential InSAR (DInSAR) is the only tool capable of measuring geological-scale strains from orbit and is particularly effective across high strain rate terrane margins, in which LoS displacements may be 10 mm a−1 or more. Combining LoS displacements derived from DInSAR sets in ascending and descending (opposite look) orbits allows the vertical and at least one of the horizontal components of displacement to be isolated. Two complementary methods are commonly used to detect displacements as small as 1 mm a−1, even in the absence of an earthquake. Combining these techniques with opposite look sets to isolate components of movement means that even the low strain deformation of terrane interiors is detectable with DInSAR.