Crustal Decoupling and Mantle Dynamics on Venus: Implications for Earth-Like Planets

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. in apparently featureless areas InSAR: • Unwrapped DEM at 27 m spatial and ~5 cm vertical resolution • Most suited to smooth terrain; fails if coherence lost over ~90 minutes Stereo: • Achieves topographic data at better than 250 m spatial and 20 m vertical resolution • Works best in rough areas, complementing interferometric topography [R Herrick] 28th October 2015 -- VEXAG 13 Slide 17 © Rich Ghail Venus Mission Plans in Europe Understanding the character and extent of different surface NovaSAR-S Airborne Demonstrator materials requires polarimetric data. Terrestrial studies show that the HV and VH polarisations states are almost identical, so that only HH, VV, and HV polarised data are required. VenSAR can transmit and receive bursts of both horizontal and vertical polarisations, allowing a mix of HH, VV, HV polarised images to be obtained. Burst mode causes scalloping that degrades the along track image resolution by a factor of 2N + 1, where N is the number of polarisation states, hence the degradation is a factor of 7. Polarimetric mapping will normally have a resolution of 160 m but a maximum 1-look resolution of 17 m is Although Venus lacks vegetation, Venera lander images show achievable in high resolution mode. a variety of surface materials that can be distinguished in multipolar imagery. [© Airbus Defence and Space]

28th October 2015 -- VEXAG 13 Slide 18 © Rich Ghail Venus Mission Plans in Europe 5 km

Sentinel-1 VV-VH-HH 120m image (left) pan-sharpened with 9-look 30m VV image (right) of mid-Atlantic rift, Iceland.

28th October 2015 -- VEXAG 13 Slide 19 © Rich Ghail Venus Mission Plans in Europe The 2 m diameter metallic body and coiled antenna array of the Venera landers will contrast strongly with the Venus surface. Increasing the transmit power and bandwidth to the maximum sustainable permits a 40 km wide swath at 2·4 m resolution (1 look), in which the landers will be identifiable as a very bright spot in the terrain. This high resolution mode will also be useful for imaging canali, tesserae and other features of geological interest.

28th October 2015 -- VEXAG 13 Slide 20 © Rich Ghail Venus Mission Plans in Europe Sliding spotlight mode allows imaging of a 5 x 10 km area with multiple looks at just 1 m resolution, sufficient to identify the landers and discriminate human-scale features at other selected targets.

Sliding spotlight image acquired by TerraSAR-X over the Chuquicamata copper mine, Chile. The range is horizontal, and the azimuth is vertical, with near range on the left side. The image dimensions are 6·8 km × 10·9 km (azimuth × slant range). [Prats et al. 2010] 28th October 2015 -- VEXAG 13 Slide 21 © Rich Ghail Venus Mission Plans in Europe VIRTIS has mapped the hot surface at 1 μm using emissivity data [Helbert, Müller, et al. 2008 & Müller, Helbert et al. 2009, 2010]

VEM-M spectral bands and science themes

Key Parameter Value Instrument Concept Pushbroom design FOV / swath 60° / 250 km Detector SOFRADIR “Neptune” 500 X 256 HgCdTe array Cooled focal plane 150 K, pulse-tube cooler 14 spectral bands Bandwidth < 10 nm Variation < 1nm Processed Data Rate 190 kb/s (1 Mb/orbit) Mass / Power (CBE) ~5.4 kg / ~18.5 W Volume 30 cm x 30 cm x 40 cm

28th October 2015 -- VEXAG 13 Slide 22 © Rich Ghail Venus Mission Plans in Europe VEM-H is a spectrometer probing the near-infrared nightside windows with very high spectral resolution (resolving power ~ 40,000). It will: • Quantify SO₂, H₂O and HDO in the lower atmosphere • Characterise of volcanic plumes • Detect other sources of gas exchange with the surface • Complement VenSAR and VEM-M surface observations

E. Marcq et al. (Venus Express); L. Esposito et al. (earlier data); image ESA/AOES Medialab

VEM-U is a small, light, UV spectrometer which will map mesospheric SO₂ abundances on the dayside of Venus. Left: the optical assembly, which is inverted and mounted on a Together with VEM-M and VEM-H it will baseplate on the underside of the radiator. link surface, tropospheric and mesospheric Right: the SOFRADIR detector for NOMAD on ExoMars. changes in SO₂, H₂O and other gases.

28th October 2015 -- VEXAG 13 Slide 23 © Rich Ghail Venus Mission Plans in Europe A Radar Sounder Instrument for EnVision

L. Bruzzone1, F. Bovolo2, R. Orosei3, D. Castelletti1, R. Seu4

1 Dept. of Information Engineering and Compuoter Science, University of Trento, Trento, Italy, 2 Fondazione Bruno Kessler, Trento, Italy 3 INAF, Bologna, Italy 4 University of Ra ma “La S pienza”, Roma, Italy

Corresponding author: [email protected]

1. Introduction 2. Radar Sounding of Venus Many open science questions of the ESA M-class EnVision mission proposal are related to the characterization of The use of a low frequency nadir looking radar sounder can provide the ideal complementary information to both the surface and the subsurface of Venus. Given the atmospheric conditions and the properties of the surface, the SAR data obtained by Magellan and the information acquired by the C-band (or S-band) interferometric SAR. some of the key science questions and the related science goals can be effectively addressed only by using This would result in a full and detailed investigation of the surface and subsurface geology of Venus. properly designed radar instruments. Currently, the use of a C-band (or S-band) SAR system with interferometric capabilities is considered in the core payload. This is aimed to address science goals related to the measurements A radar sounder, which can operate at VHF or UHF central frequencies, can acquire fundamental information on of the topography and of the surface displacements according to differential interferometric techniques. However, subsurface geology which cannot be achieved with the InSAR system. In particular it can focus on mapping the this system can only study the surface vertical structure and cannot provide any direct measure on the subsurface. vertical structure of geologic units by exploring the subsurface properties of tessera, plains, lava flows and impact Accordingly, in this poster we propose and discuss a complementary radar instrument which is a low-frequency debris. The sounder could analyze the shallow subsurface of Venus to detect and map geological structures and to identify mechanical and dielectric interfaces. radar sounder. A radar sounder instrument also provides information on the surface in terms of roughness, composition and 3. Science goals dielectrical properties at wavelength completely different from those of SAR, thus allowing a better understanding of the surface properties. Moreover, a fusion of the InSAR data (both intensity, topography and displacement The Radar Sounder for EnVision can acquire information on the shallow subsurface with the following main variables) with the sounder data would result in an exceptional capability to understand the link between the scientific goals: surface and subsurface processes on Venus. Note that depending on the design of the system, the sounder could also acquire measurements for characterizing the ionosphere. • Characterization of the different stratigraphic and structural patterns of the subsurface. • Study the volcanism phenomena and their impact on the geological evolution of the Venusian topography. • Detection of subsurface structures non directly linked with surface. 4. Heritage and Examples of Radargrams Relevant to Venus • Analysis of the materials in the surface and subsurface and their metamorphism linked to the burial process. • Synergistic analysis of the data provided by SAR and radar sounder sensors to study the evolution of the planet. • MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on ESA Mars Express [2] and SHARAD • Analysis of the total electron content of the ionosphere. (Shallow Radar) on NASA Mars Reconnaissance Orbiter [3]. • RIME (Radar for Icy Moon Exploration) on ESA Jupiter Icy Moon Explorer [4]-[5]. One of the main issues for the design of the radar sounder instrument for EnVision concerns the physical and SHARAD radargram over a electromagnetic modelling of the surface and subsurface targets. Magellan radar measurements provided portion of western Medusae information on terrain dielectric properties and surface roughness. We can distinguish two main areas: Fossae Formation, a low- density pyroclastic deposit spanning across the crustal Highland areas which are mostly characterized by high values of the dielectric permittivity ε (e.g., around 20), dichotomy of Mars. The supposedly because of rocks with metal content; and high surface roughness. deposit labelled "North Hill“ (nh) is about 500 m thick Lowland areas are composed by basalt materials with expected high porosity that entails an expected value of (taken from [6]).

ε = 5 ± 0.9. Lowland areas present smoother topography.

Highlands (about 20% of the Venus area) may represent a critical scenario for the penetration the radar A Radar Sounder Instrument for EnVision electromagnetic waves, whereas lowland (about 80% of the Venus area) have dielectric constants that are SHARAD radargram across suitable for sounding. two distinct lava flows emanating from Ascraeus The ionosphere of Venus can affect radar signal propagation, but offers additional opportunities for science. The Mons, Mars. Estimates of dielectric permittivity are maximum plasma frequency on the day side is around 5-6 MH1z, below 1 MHz on t2he night side. Signals 3below 1 4 between 6 and 17, loss those frequencies cannot propagate toL. the Bruzzonesurface. Similarly to ,M Far.s , Bovoloa radar signal w,i llR. be dOroseiistorted in cro,s siD.ng Castelletti , R. Seu tangent is in the range 0.01- the dispersive plasma, but such distortion can be corrected, and the correction algorithm can pro vide information 0.03. These values are on the total electron content of 1t he ionosphere. consistent with those of Dept. of Information Engineering and Compuoter Science, University of Trento, Trento, Italy, terrestrial and lunar basalts 2 Fondazione Bruno Kessler, Trento, Italy (taken from [7]).

3 INAF, Bologna, Italy 4 University of Ra ma “La S pienza”, Roma, Italy

Corresponding author: [email protected]. tn. Prite liminary Instrument Parameters The sounder can be designed to study either the shallow subsurface with high vertical resolution or to obtain 1. Introduction 2. Radar Sounmdoindegr aotef pVeenneturast i o n with reduced vertical resolution. Taking into account the plasma frequency, the lowest central frequency that can be used is of 6 MHz. The table below reports a preliminary identification of the possible ranges Many open science questions of the ESA M-class EnVision mission proposal are related to the characterization of The use of a lowi nfr weqhuicehn sceyl encatidnigr tlhoeo ksoinugn draedr apra rsaomuentdeersr. can provide the ideal complementary information to both the surface and the subsurface of Venus. GivTheen the Radaratmosph eSounderric conditions forand EnVisionthe properties canof th eacquire surface, informationthe SAR da tona ob thet ained by Magellan and the information acquired by the C-band (or S-band) interferometric SAR. some of the key science questions and the related science goals can be effectively addressed only by using This would result in a full anTdr adnestmaiiltetedd i ncveensttriagla ftrieoqnu eonf ctyh e(f cs)u rface andIn s tuhbes ruarnfagcee 6 g -e 3o0l oMgHy zo f Venus. properly designed radar instruments. Currentlyshallow, the use of subsurfacea C-band (or S-ba nwithd) SAR thesystem following with interfero mmainetric scientific goals: capabilities is considered in the core payload. This is aimed to address science goals related to the measurements A radar sounder, which canT roapnesmraittete adt b VanHdFw oidr tUh H(BFw c)e ntral frequenIcni eths,e crang ea c2q -u 1ir0e MfuHnzd amental information on subsurface geology which cannot be achieved with the InSAR system. In particular it can focus on mapping the of the topography and of the surface displacem•entsCharacterisation according to differential i nofter fetherome differenttric technique sstratigraphic. However, and structural Antenna type Dipole (deployable) this system can only study the surface vertical structure and cannot provide any direct measure on the subsurface. vertical structure of geologic units by exploring the subsurface properties of tessera, plains, lava flows and impact Accordingly, in this poster we propose and discusspatterns a compleme noftar ythe rada rsubsurface. instrument which is a low-frequency debris. The sounder could aAnnatleyznen ath deim shenasllioown subsurface of Venus tToB dDe (tdeecpte annddin mg oanp tgheeo cleongtircaal l fsrterquucetuncrey)s and to identify mechanical and dielectric interfaces. radar sounder. Power 30 W False-color representatio•n of VStudyenus surface thetopogra pvolcanismhy, data phenomenaVenus RMS meter-sc aandle surfa cetheir roughnes simpact [1]. on the A radar sounder instrumenAtl oanlsgo t rparcok vriedseoslu itniofonr mation on the surf

The sounder can be designed to study either the shallow subsurface with high vertical resolution or to obtain moderate penetration with reduced vertical resolution. Taking into account the plasma frequency, the lowest central frequency that can be used is of 6 MHz. The table below reports a preliminary identification of the possible ranges in which selecting the sounder parameters.

Transmitted central frequency (fc) In the range 6 - 30 MHz

Transmitted bandwidth (Bw) In the range 2 - 10 MHz Antenna type Dipole (deployable) Antenna dimension TBD (depending on the central frequency) Power 30 W False-color representation of Venus surface topography, data Venus RMS meter-scale surface roughness [1]. acquired by Magellan satellite [1]. Along track resolution < 1 km Across track resolution < 5 km 5. Clutter Vertical resolution 75 m (Bw=2 MHz) - 15 m (Bw=10 MHz) (vacuum) Clutter is given by off-nadir surface reflections reaching the radar at Estimated maximum penetration depth 1.5 Km (fc=6 MHz) - 600 m (fc=30 MHz) the same time as subsurface nadir reflections, thus potentially 300 – 10000 kbps (depending on selected Data rate masking them. The strength of clutter is controlled by statistical parameters and operation scenarios) parameters of the topography of natural surfaces scattering the Mass (without antenna) 10 kg radiation. Size 37×25×13 cm The signal ambiguity introduce by the clutter could limit data analysis Pointing requirements Nadir and interpretation.

Different approaches are possible for identifying and reducing clutter effects. These approaches require the availability of Digital Terrain Model (DTM) for identifying clutter features in areas where the surface is rough with respect to the considered wavelength. This should not be a problem in EnVision given the SAR instrument and its 7. Conclusions interferometric capababilities that can acquire topographic information at the scale required for clutter mitigation in post-processing. This poster summarizes the potentials of a radar sounder for Venus. A radar sounder can be a very effective instrument for complementing the suite of payloads in EnVision.

The main gain in terms of scientific return is that the radar sounder can perform measurements at either shallow or moderate depth of the subsurface of Venus. These measurments integrated with all the information extracted by the C-band SAR system would result in an exceptional capability to study jointly surface and subsurface properties and phenomena of Venus.

Preliminary studies and experience gained with MARSIS and SHARAD on areas on Mars having similar properties to what expected in some part at of Venus point out the feasibility of the sounding and the rich amount of information that can be extracted. Further studies are currently in progress for reducing the uncertainty on the expected Example of L2 products on SHARAD data: (a) radargram obtained by azimuth and range processing; (b) simulation of clutter effects based on the DTM of the target; (c) false color composition that superimposes the radargram with the detected clutter (in green subsurface scenario. the measured data, in white the surface reflection and the detected surface clutter) [8].

[1] Ford, P. G., Pettengill, G. H. Venus topography and kilometer-scale slopes. Journal of Geophysical Research 97, 13103. 1992. [5] Bruzzone, L., Alberti, G., Catallo, C., Ferro, A., Kofman, W., Orosei, R., Sub-Surface Radar Sounding of the Jovian Moon Ganymede, [2] Picardi, G., and 33 colleagues. Radar Soundings of the Subsurface of Mars. Science 310, 1925-1928. 2005. Proceedings of the IEEE, Vol. 99, No.5, 2011, pp. 837-857. [3] Seu, R., and 11 colleagues. SHARAD sounding radar on the Mars Reconnaissance Orbiter. Journal of Geophysical Research (Planets) [6] Carter, L. M., and 12 colleagues, Shallow radar (SHARAD) sounding observations of the Medusae Fossae Formation, Mars, Icarus, Volume 112, 5. 2007. 199, Issue 2, February 2009. [4] Bruzzone, L., and 15 colleagues. RIME: Radar for Icy Moon Exploration, IGARSS 2013. [7] Carter, L. M., and 8 colleagues, Dielectric properties of lava flows west of Ascraeus Mons, Mars. Geoph. Research Letters 36, 23204. 2009. [8] Ferro, A., Bruzzone, L., "Automatic Extraction and Analysis of Ice Layering in Radar Sounder Data," Geoscience and Remote Sensing, IEEE Transactions on , vol.51, no.3, pp.1622,1634, March 2013. A Radar Sounder Instrument for EnVision

L. Bruzzone1, F. Bovolo2, R. Orosei3, D. Castelletti1, R. Seu4

Corresponding author: [email protected]

ε = 5 ± 0.9. Lowland areas present smoother topography.

3 INAF, Bologna, Italy 4 University of Ra ma “La S pienza”, Roma, Italy

Corresponding author: [email protected]. tn. Prite liminary Instrument Parameters The sounder can be designed to study either the shallow subsurface with high vertical resolution or to obtain 1. Introduction 2. Radar Sounmdoindegr aotef pVeenneturast i o n with reduced vertical resolution. Taking into account the plasma frequency, the lowest central frequency that can be used is of 6 MHz. The table below reports a preliminary identification of the possible ranges Many open science questions of the ESA M-class EnVision mission proposal are related to the characterization of The use of a lowi nfr weqhuicehn sceyl encatidnigr tlhoeo ksoinugn draedr apra rsaomuentdeersr. can provide the ideal complementary information to both the surface and the subsurface of Venus. GivTheen the Radaratmosph eSounderric conditions forand EnVisionthe properties canof th eacquire surface, informationthe SAR da tona ob thet ained by Magellan and the information acquired by the C-band (or S-band) interferometric SAR. some of the key science questions and the related science goals can be effectively addressed only by using This would result in a full anTdr adnestmaiiltetedd i ncveensttriagla ftrieoqnu eonf ctyh e(f cs)u rface andIn s tuhbes ruarnfagcee 6 g -e 3o0l oMgHy zo f Venus. properly designed radar instruments. Currentlyshallow, the use of subsurfacea C-band (or S-ba nwithd) SAR thesystem following with interfero mmainetric scientific goals: capabilities is considered in the core payload. This is aimed to address science goals related to the measurements A radar sounder, which canT roapnesmraittete adt b VanHdFw oidr tUh H(BFw c)e ntral frequenIcni eths,e crang ea c2q -u 1ir0e MfuHnzd amental information on subsurface geology which cannot be achieved with the InSAR system. In particular it can focus on mapping the of the topography and of the surface displacem•entsCharacterization according to differential i nofter fetherome differenttric technique sstratigraphic. However, and structural Antenna type Dipole (deployable) this system can only study the surface vertical structure and cannot provide any direct measure on the subsurface. vertical structure of geologic units by exploring the subsurface properties of tessera, plains, lava flows and impact Accordingly, in this poster we propose and discusspatterns a compleme noftar ythe rada rsubsurface. instrument which is a low-frequency debris. The sounder could aAnnatleyznen ath deim shenasllioown subsurface of Venus tToB dDe (tdeecpte annddin mg oanp tgheeo cleongtircaal l fsrterquucetuncrey)s and to identify mechanical and dielectric interfaces. radar sounder. Power 30 W False-color representatio•n of VStudyenus surface thetopogra pvolcanismhy, data phenomenaVenus RMS meter-sc aandle surfa cetheir roughnes simpact [1]. on the A radar sounder instrumenAtl oanlsgo t rparcok vriedseoslu itniofonr mation on the surf