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L.J. Harcke (Stanford University), B.J. Butler (National Radio Astronomy Observatory), H.A. Zebker (Stanford University), M.A. Slade, R.F. Jurgens (Jet Propulsion Laboratory)
Radar observations of Callisto in February 2002 by the Goldstone Solar System Radar and the Very Large Array in bistatic configuration have completed a global mapping campaign started in December 2000. We present full disk 3.5~cm radar albedo maps of Ganymede and Callisto acquired during the January 2002 and December 2000 Jovian oppositions. Circular polarization was transmitted by the Goldstone antenna and both circular polarizations were received and recorded by the VLA. The VLA antenna elements were at maximal extent (A-configuration) , giving a resolution at Jovian range of 360~km. The leading hemisphere total integrated disk radar albedos of Ganymede were measured to be 0.89 and 0.63 for the same-sense (SC) and opposite-sense (OC) polarizations, respectively. The integrated disk radar albedos of Callisto were 0.40 (SC) and 0.31 (OC). These numbers are within a few percent of previous 3.5 cm monostatic observations (Ostro et al. 1992). The Goldstone/VLA instrument does not exhibit the north/south folding of monostatic radar observations, providing a global unambiguous map. The radar albedo is overlayed with Galileo orbiter optical imagery to allow the identification of terrains which cause enhanced backscatter and polarization inversion. Current scattering models involve deep penetration of the radar wave into a nearly transparent icy subsurface, combined with multiple scattering from buried discontinuities (Hapke 1990).
This work is supported by the Planetary Astronomy program of the National Science Foundation. The Goldstone Solar System Radar is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The VLA is operated by Associated Universities, Inc., under contract with NSF.
Ostro, S.J. et al. (1992) JGR 97, 18227. \\ Hapke, B. (1990) Icarus 88, 407.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.