Venus Lab and Technology Workshop (2015) 4010.pdf

VISAR: A Next Generation Inteferometric Radar for Venus Exploration, S. Hensley1, S. Smrekar1, S. Shaffer1, M. Paller1, H. Figueroa1, A. Freeman1, R. Hodges1, P. Walkemeyer1, 1Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA, 91109, Scott.Hensley@jpl.nasa.gov

Introduction: Magellan, a NASA mission to Ve- found an optinal wavelength of about 3.8 cm when nus in the early 1990’s, mapped nearly the entire sur- operating with a look angle (angle from nadir) of 30°. face of Venus with an S-band (12 cm) synthetic aper- The radar operates with a bandwith of 20 MHz which ture radar and microwave radiometer and made radar gives a range resolution of about 7.5 m or 15 m when altimeter measurements of the topography, [1]. These projected onto the ground. The azimuth or along-track measurements revolutionized our understanding of the resolution is about 2 m, hence we have at least 7-8 geomorphology, geology and geophysical processes looks for imagery and around 1800 looks for topo- that have shaped the evolution of the surface of Venus. graphic products. In order to be able the downlink the However, the lack of finer resolution imagery and to- data required to make a global product it is necessary pography of the surface than that obtained by the Ma- to do onboard image formation and interferogram gen- gellan mission has hampered the definitive answer to eration which provides an approximate 1000 fold re- key questions concerning the processes and evolution duction in data volume compared to the raw radar data. of the surface of Venus. The Venus Emissivity, Radio By collecting both asecending and descending orbits Science, InSAR Topography And Spectroscopy everywhere we expect to get nearly global coverage (VERITAS) Mission is a proposed mission to Venus with only minor gaps due to layover and shadow. Ex- designed to obtain high resolution imagery and topog- tremely steep slopes can also be constrained with high raphy of the surface using an X-band radar configured resolution imaging. We will use tiepoints between as a single pass radar interferometer (called VISAR) overlapping orbits for ephemneris improvemnts and a coupled with a multispectral NIR emissivity mapping “bundle adjustment procedure” in order to seamlessly capability. mosaic the 14.4 km image strips in final topographic Science Objectives: VERITAS has as major sci- and image products. entfic goals to: 1) understand Venus’ geologic evolu- In addition to the single pass interferometry for tion, 2) determine what geologic processes are current- topographic measurement we also intend to use repeat ly operating, and 3) find evidence for past or present pass observations of selected targets (e.g. 200 by 200 water. km) to look for currently active deformation of the Mission Overview: VISAR will operate from Venus surface. Using repeat pass obsevations we can slightly eceentric nearly polar orbit, 88.5° inclination detect surface deformation at the centimeter scale and angle orbit, with an average altitude of approximately detect sub-wavelength distrubances to the surface be- 220 km. Operating for a period of three Venus days or tween observations. Although there will be 243 days cycles (3x243 Earth days) VISAR will generate image- between observations we know the atmosphere and ry and topography globally for the surface of Venus. surface allow such observations based on experience VISAR will map surface topography with a spatial with Magellan data [2]. resolution of 250 m and 5 m vertical accuracy and References: generate radar imagery with 30 m spatial resolution [1] R. S. Saunders, A. J. Spear, P. C. Allin, R. S. globally and 15 m resolution for approximately 15% of Austin, A. L. Berman, R. C. Chandlee, J. Clark, A. V. the planet surface. These capabilities represent an or- Decharon, E. M. De Jong, D. G. Griffith, J. M. Gunn, der of magnitude or better improvement of the Magel- S. Hensley, W. T. K. Johnson, C. E. Kirby, K. S. lan system and are expected to reveal definitive infor- Leung, D. T. Lyons, G. A. Michaels, J. Miller, R. B. mation on key geologic processes not possible with the Morris, R. G. Piereson A. D. Morrison, J. F. Scott, S. J. Magellan data. Shaffer, J. P. Slonski, E. R. Stofan, T. W. Thompson, Intrument Overview: The VISAR instrument is and S. D. Wall. Magellan Mission Summary. Journal an X-band, 3 cm wavelength interferometric radar de- of Geophyiscal Research, 97:13,067–13,09, 1992. signed to meet the topographic mapping and imagery [2] Hensley, S., and S. Shaffer, Repeat pass radar requirements. Wavelength selection was predicated on observations of Venus from the Magellan Radar Sys- overcoming the losses due to transmission through the tem, Proc. 41st Lunar and Planet. Sci. Conf., 2010. thick Venus atmosphere (loss goes as f2 in dB) and Acknowledgements: This research was conducted working with a constrained interferometric baseline at the Jet Propulsion Laboratory, California Institute of length of 3.1 m, the maximal achievable on the space- Technology, under contract with the National Aero- craft without going to a deployment mechanism. We nautics and Space Administration.