Richard Ghail Thomas Widemann Colin Wilson Lead Proposer Programme Management Lead Science Investigation Lead 28th October 2015 -- VEXAG 13 © Rich Ghail Venus Mission Plans in Europe Outstanding Questions and Debate: • Almost nothing known about the Venus interior • Why is the crater distribution at odds with the geology? • Are tesserae old or special? • Is large scale deformation a thing of the past? • How active are the volcanoes? Recent Observations: • Some evidence for pyroclastic materials • Sulphur cycle probably most Based on Magellan Global Vector Data Record (G. Leonard Tyler) important What new data are required? • Evidence for a weathering and • Higher resolution imagery and • Exchange rate between the interior sedimentary cycle topography and exterior • Constraints on interior structure • Rates of surface change/activity 28th October 2015 -- VEXAG 13 Slide 2 © Rich Ghail Venus Mission Plans in Europe Radiometric resolution (sensitivity) across a large dynamic range is critical to distinguish features in bright and dark areas Low spatial resolution prevents identification of most geological relationships and changes [Herrick 2014] 28th October 2015 -- VEXAG 13 Slide 3 © Rich Ghail Venus Mission Plans in Europe Changes in slope have been incorrectly interpreted as different units from which an onlap relationship is inferred. In fact, the differences are mostly attributable to slope angle and talus. Our understanding of Venus today is no better than was our understanding of Mars after Viking [JPL 400-528H 6/94] SIR-C image of Furnace Creek alluvial fan, [Ivanov and Head 2015] Death Valley 28th October 2015 -- VEXAG 13 Slide 4 © Rich Ghail Venus Mission Plans in Europe The conventional view is that all volcanic features are produced by hot spots (plumes) of different sizes. The 6 or 7 volcanic rises are most likely produced by core-mantle boundary plumes, with smaller features formed by plumes from shallower depths. © 2007 Eric H. Christiansen and W. Kenneth Hamblin Corona and related features most likely result from magmatic intrusion. Variations in SO₂ abundance may record large volcanic eruption events, and would imply abundant volatiles in the source magma. E. Marcq et al. (Venus Express); L. Esposito et al. (earlier data); image ESA/AOES Medialab 28th October 2015 -- VEXAG 13 Slide 5 © Rich Ghail Venus Mission Plans in Europe Outstanding Questions and Debate: Goal Measurement Resolution Coverage • Almost nothing known about the Surface change < ±1 cm a⁻¹ at 10–50 m spatial >20% global Venus interior Geomorphology Images at 10–50 m spatial Global • Why is the crater distribution at Topography at 10–50 m vertical, 100–500 m spatial Global odds with the geology? Specified targets Images at 1–10 m spatial As required • Are tesserae old or special? Subsurface structure Profiles at 10–50 m vertical and 100–500 m spatial Global • Is large scale deformation a thing of Thermal emissivity Signal to noise >100 at <50 km spatial Global the past? SO₂ concentration < ±1% at <300 km spatial and 30–40 km altitude Global • How active are the volcanoes? H₂O concentration < ±10% at <300 km spatial and <15 altitude Global D/H ratio < ±10% at <300 km spatial and <15 altitude Global Recent Observations: Gravity field Spherical harmonic degree and order 120 Uniform • Some evidence for pyroclastic Spin Rate < ±10⁻⁸ (1 minute in one Venus day) Global materials Spin Axis < ±0·001° in right ascension and declination North Pole • Sulphur cycle probably most Based on Magellan Global Vector Data Record (G. Leonard Tyler) important What new data are required? • Evidence for a weathering and • Higher resolution imagery and • Exchange rate between the interior sedimentary cycle topography and exterior • Constraints on interior structure • Rates of surface change/activity 28th October 2015 -- VEXAG 13 Slide 6 © Rich Ghail Venus Mission Plans in Europe Shrouded in permanent clouds, the 90 bar, 750 K 60 Venus atmosphere is prohibitive for surface rovers and opaque at wavelengths shorter than ~3·5 cm. S-Band 55 X-Band Total one-way losses are (add 3 dB for two-way): • 6·20 dB at 3·8 cm, 8·4 GHz X-band 50 • 1·69 dB at 5·6 cm, 5·4 GHz C-band km • 0·55 dB at 9·4 cm, 3·2 GHz S-band 45 [based on Muhleman 1969] EnVision’s InSAR coherence requirement drives our choice for an S-band radar. Altitude in 40 In other respects the atmosphere is benign: 35 • The total electron count is <1 TeV • IR brightness temperature ~50 K cooler than Earth • Drag-free orbits above 220 km altitude 30 0 0.01 0.02 0.03 0.04 0.05 H₂SO₄ Losses in dB/km 28th October 2015 -- VEXAG 13 Slide 7 © Rich Ghail Venus Mission Plans in Europe NovaSAR will consist of four small NovaSAR being assembled at SSTL [Thales Alenia Space] low cost SAR satellites providing continuous global environmental management and disaster monitoring. The first is being funded by the UK government for launch in 2016. [SSTL] EnVision is a proposed ESA M-class mission to Venus designed to find out what made Earth’s closest neighbour so different. It will carry a subsurface sounder, emissivity mapper and spectrometer, and its primary instrument, the NovaSAR-S based VenSAR. 28th October 2015 -- VEXAG 13 Slide 8 © Rich Ghail Venus Mission Plans in Europe The reverse side of each phase centre has: • a power conditioning unit, • a 115 W RF transmit unit, • a radiator unit, and • a receive/beam control unit, making for an independently controllable, fully scalable array. The VenSAR antenna consists of 24 of these phase centres arranged in 6 columns of 4 rows spread over 3 panels (2 columns per panel), oriented with the orbit track along the major axis. 28th October 2015 -- VEXAG 13 Slide 9 © Rich Ghail Venus Mission Plans in Europe Multi-look Spatial Radiometric content resolution resolution 5·47 m x 0·6 m (6 columns x 4 rows) 1 look S-band, 3·2 GHz, upto 182 MHz Tx bandwidth 3.7 dB DC Power: 820 W at 5% Tx duty ratio 3 m x 3 m 1874 W at 20% Tx duty ratio Selectable single polarisation: HH, VV and HV 3 looks 2.5 dB Along track resolution is fixed at ~3 m Across track resolution is a trade off between 4.5 m x 4.5 m data rate, spatial and radiometric resolution: 9 looks 9 looks is the best compromise: 1.6 dB 27 m square pixels at 53 Mbps at 4% Tx 7 m x 7 m High resolution is achieved by maximising 81 looks bandwidth: 2 x 3 m single look for 6 m square 0.6 dB pixels at 6 looks at 856 Mbps at 20% Tx 10.5 m x 10.5 m Image sequence showing impact of multi-looking; normally higher Sliding spotlight can achieve 1 m resolution spatial resolution reduces number of looks possible. Simulation based on airborne NovaSAR-S test data. [© Airbus Defence and Space] 28th October 2015 -- VEXAG 13 Slide 10 © Rich Ghail Venus Mission Plans in Europe 28th October 2015 -- VEXAG 13 Slide 11 © Rich Ghail Venus Mission Plans in Europe 28th October 2015 -- VEXAG 13 Slide 12 © Rich Ghail Venus Mission Plans in Europe Operating Mode Transmit Mean RF Input Image Swath Data Rate Duty Ratio Power Power† Duration Width Stereo 3% + 10% 179 W 898 W 11·5 min 45 km 139 Mbps Interferometry 4% 110 W 660 W 16·1 min 43 km 53 Mbps Polarimetry 4% 110 W 660 W 15·3 min 45 km 81 Mbps High Resolution 20% 552 W 1874 W 5·0 min 40 km 856 Mbps Sliding Spotlight 20% 552 W 1874 W 2·184 s 10 km 591 Mbps 28th October 2015 -- VEXAG 13 Slide 13 © Rich Ghail Venus Mission Plans in Europe Left: 110 m resolution, 5-look image posted at 75 m per pixel to simulate a Magellan image from Venus. Note that the volcanic cone suffers from layover. 10 km Right: Simulated standard resolution (27 m) 9-look VenSAR image. Layover is corrected using the stereo-derived 135 m resolution DEM. In addition to higher spatial resolution and reduced noise, the image has greater sensitivity and a factor of 4 improvement in radiometric resolution. 10 km [All images derived from Sentinel 1a data] 28th October 2015 -- VEXAG 13 Slide 14 © Rich Ghail Venus Mission Plans in Europe Left: 110 m resolution, 5-look image posted at 75 m per pixel to simulate a Magellan image from Venus. Note that the volcanic cone suffers from layover. 10 km Right: Simulated high resolution (6 m) 9-look VenSAR image. This simulation uses scale 3-look 14 m Sentinel-1 data; VenSAR will achieve better spatial and radiometric resolution. 10 km [All images derived from Sentinel 1a data] 28th October 2015 -- VEXAG 13 Slide 15 © Rich Ghail Venus Mission Plans in Europe Pass to Pass InSAR: InSAR detection of • Increases the quality of InSAR post-seismic observations by minimizing atmospheric deformation. phase distortions while maximizing [Peltzer 1997] coherence • Variance of estimated topography and 7½ hour interferogram of deformation parameters can be reduced Venus north pole from • Long spatial baselines increases Magellan topographic resolution [Goldstein et al. pers. comm.] • Helps separate topographic and deformation related phase components • Can be achieved using electronic shift in transmitted frequency, reducing bandwidth and data rates Provides initial results in hours not months Magmatic inflation at Etna (ERS data) 28th October 2015 -- VEXAG 13 Slide 16 © Rich Ghail Venus Mission Plans in Europe Resolution requirement: • Globally to better than a few tens of metres (Magellan was >100 m) • Resolve flow boundaries, tesserae fault blocks, crater floor darkening • Individual lava flows, canali, boundaries, etc.