Unambiguous 3.5 cm Reflectivity Images of Ganymede and Callisto From Bistatic Goldstone/VLA Radar Observations

Details Unambiguous 3.5 cm Reflectivity Images of Ganymede and Callisto From Bistatic Goldstone/VLA Radar Observations Unambiguous 3.5 cm Reflectivity Images of Ganymede and Callisto From Bistatic Goldstone/VLA Radar Observations

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p12b0498h&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #P12B-0498

Physics

5464 Remote Sensing, 5470 Surface Materials And Properties, 6218 Jovian Satellites

Scientific paper

We present 3.5 cm wavelength radar reflectivity images of Ganymede and Callisto obtained by using the Goldstone radar and the VLA in a bistatic configuration. Although lower resolution than previous monostatic radar observations of these satellites (360 km vs. 75 km), the bistatic geometry and VLA image synthesis lead to albedo maps that are not subject to the usual range-Doppler folding and superposition of the northern and southern hemispheres. The data were acquired during the December 2000 Jovian opposition. For this series of observations, Goldstone transmitted an average power of 450 kilowatts continuous wave to the moon under study. Both circular polarizations were received in VLA spectral line mode. Aperture synthesis resolves the moon in plane-of-sky (RA and DEC) coordinates at angular resolution inversely proportional to the longest baseline of the VLA. As the array was maximally extended (A-configuration) for the observations, the best resolution possible with the Goldstone/VLA radar instrument was obtained. Observations at radio wavelengths are unique in their ability to probe beneath the surfaces of these bodies, possibly yielding information on structures that are not visible in optical images. Hence, we compare the new radar maps with Galileo orbiter images of the Jovian moons. The electromagnetic theory of radar echoes from the icy Galilean satellites is still not completely understood, as they exhibit very high backscatter albedo along with a peculiar reversal of polarization. However, we should be able to identify any coincidence of radar scattering properties and obvious surface features. We thus use the data acquired here to map the spatial variations in radar cross section across the disk of these moons and correlate them with optical albedo images, and investigate the spatial extent and absolute cross section of the coherent backscatter phenomena (Hapke, 1990) noted in 13~cm monostatic radar imaging with the Arecibo radar (Ostro et al., 1992; Harcke et al., 2001). Overlaying the radar images on the recent Galileo images will permit identification of particular radar surface features with optically-seen and studied features. The spatially resolved data permit tentative identification of the terrains which produce enhanced backscatter from the surfaces of these icy moons, and might eventually suggest candidate resurfacing processes. Harcke, L.J. (2001). 32nd LPSC, abstract 1369. Hapke, B. (1990). Icarus, 88, 407. Ostro, S.J. et al. (1992). JGR, 97, 18,227.

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