37th DPS Meeting, 4-9 September 2005
Session 61 Planetary Rings
Poster, Thursday, September 8, 2005, 6:00-7:15pm, Music Lecture Room 5

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[61.15] Cassini Radio Occultations of Saturn's Rings: Scattered Signal and Particle Sizes

F. Thomson (Stanford U.), K. Wong, E. Marouf (San Jose State U.), R. French (Wellesley Coll.), N. Rappaport (JPL), C. McGhee (Wellesley Coll.), A. Anabtawi, S. Asmar, E. Barbinis, D. Fleischman, G. Goltz, D. Johnston, D. Rochblatt (JPL)

Eight Cassini radio occultations of Saturn's rings were conducted from May 3 to September 5, 2005. During any given occultation, Cassini transmits Ka-, X-, and S-band sinusoidal signals (0.94, 3.6, and 13 cm-wavelength) through the rings. Spectral analysis of the perturbed signals received at stations of the Deep Space Network (DSN) reveals two distinct signal components. The first is the direct signal, a narrowband component representing the incident sinusoid emerging from the rings reduced in amplitude and changed in phase. The second is the scattered signal, a broadband component, representing near-forward scattering by ring particles. After reconstruction to remove diffraction effects, time history of the direct signal yields profiles of ring structure at resolution approaching ~0 m. Of primary concern here is the broadband component. For the first time ever, clearly detectable scattered signals were observed at all three (Ka/X/S) bands. A single X/S radio occultation by Voyager 1 in 1980 detected scattered signal at X-band only, primarily because of the small ring opening angle B=5.9\circ at the time, compared with 19.1 \leq B \leq 23.6\circ for Cassini. Time histories of the observed spectra (spectrograms) and their dependence on wavelength provide important information about physical ring properties, including abundance of meter-size particles, particle crowding, clustering, spatial anisotropy, vertical ring profile and thickness. Cassini occultation orbits were optimized to map scattering by individual ring features into nearly non-overlapping spectral bands, allowing unambiguous identification of the contribution of ring features to the computed spectrograms. We present Ka/X/S spectrograms over the full extent of the ring system and relate their behavior to observed ring structure. The spectrograms imply presence of meters-size particles throughout the ring system. Preliminary results regarding the particle size distribution and vertical ring profile of selected ring features are presented.

Contributions of personnel of the DSN are gratefully acknowledged.

The author(s) of this abstract have provided an email address for comments about the abstract: fthomson@stanford.edu

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