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J. P. Hoffman (Jet Propulsion Laboratory), P. S. Steffes (Georgia Institute of Technology)
Application of the results from laboratory measurements of the centimeter-wavelength opacity of phosphine shows that phosphine is a likely contributor to the microwave spectrum of the upper atmospheres of Saturn and Neptune (Hoffman, Steffes, and DeBoer 2001. Laboratory Measurements of the Microwave Opacity of Phosphine: Opacity Formalism and Application to the Atmospheres of the Outer Planets. Icarus 152, 172-184). The impact these findings will have on the upcoming Cassini radio scientific measurements at Saturn is estimated using a ray-tracing based radiative transfer model. By modeling the atmosphere as elliptical shells, as opposed to planar stratified or spherical shells, the oblateness of Saturn is approximated. Also, the ray-tracing engine allows for modeling spatial variations in the atmosphere and/or antenna pattern over any spatial scale required. With these features this model is better able than traditional models to estimate the brightness temperature as measured by a close-in observer such as the Cassini spacecraft at Saturn.
With the laboratory results and the new radiative transfer model, the ability of the Cassini radiometer to discern contributions to microwave emission from phosphine and ammonia in Saturn's atmosphere is examined.
This ray tracing atmospheric model is currently being updated to estimate the effects of Saturn's upper atmosphere on transmissions from (and to) the Cassini spacecraft during radio occultation experiments. Also, this preliminary radio occultation model is employed to estimate the ability of the Cassini radar/radiometer to perform Uplink radio occultation measurements.
Supported by the NASA Planetary Atmospheres Program under Grant NAG5-4190.
The author(s) of this abstract have provided an email address for comments about the abstract: james.hoffman@jpl.nasa.gov