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[18.19] Simulations of the Cassini Radio Occultation Experiments for the Atmosphere of Saturn Based on Recent Laboratory Measurements

P. N. Mohammed, P. G. Steffes (Georgia Institute of Technology)

Studies of the sensitivity of the Cassini three frequency radio link to the atmospheric constituents encountered during radio occultation are being conducted using laboratory measurements of the 9 mm opacity of phosphine and ammonia (Mohammed and Steffes, ICARUS 166, 425-435, 2003) and the centimeter wavelength opacity of these constituents measured under simulated conditions for Saturn (see, e.g., Hoffman et. al. ICARUS 152, 172-184, 2001). A computer model has been developed to simulate ray paths and the ray path parameters in the atmosphere of Saturn encountered during occultation. In conjunction with the results of the laboratory measurements this model is used to calculate attenuation profiles from phosphine and ammonia and excess Doppler shift and refractive defocusing at Ka-band (32 GHz or 9.3 mm), X-band (8.4 GHz or 3.6 cm) and S-band (2.3 GHz or 13 cm). These parameters are being determined for ingress and egress occultations on revolutions 7, 51, 54 and 70, the first of which will begin May 3, 2005. The radio occultation simulator also predicts the pressure to which each of the three frequencies can penetrate before loss of signal.

This work is supported by the NASA Planetary Atmospheres Program under grant NAG5-12122.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.