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K. Kusza, G. L. Tyler (Stanford University)
Radio occultation remote sensing of planetary atmospheres is based on the measurement of the refraction of electromagnetic waves that have tangentially passed through the planet’s atmosphere on the way from the transmitter to receiver. Since the radio wavelengths are small compared to the distance scales of the system, the waves can be approximated as rays that travel in straight lines through empty space and bend when they interact with the gas in the planet’s atmosphere.
The Abel integral transform and Bouguer’s rule relate the measured bending of the rays to the refractivity of the planet’s atmosphere as a function of height above the geoid. The Abel transform in its original form describes the path of a ray traveling in a straight line that has passed through a two-dimensional, spherically symmetric object. The standard Abel transform is modified to account for the ray bending, which is of more importance when studying dense planetary atmospheres than thin atmospheres, where there is less bending. This modified Abel transform pair relating refractivity to bending angle, and including ray bending, has only one known transform pair, in polynomial form, as derived by Eshleman (1973).
Recently, it has been suggested that characteristic atmospheric vertical structures and occultation signatures can be modeled using a superposition method of the known occultation transform pairs (Eshleman, 1996). Here, the occultation transform pair superposition method will be applied to create simple refractivity features for both the thin atmosphere approximation, essentially straight ray paths instead of bending ray paths, and the complete occultation transform pair expression corresponding to bent ray paths through dense atmospheres. A comparison of the bent and straight ray path approaches demonstrates equivalence for the thin atmosphere case and illustrates the errors introduced in the case of a dense atmosphere.
Eshleman, Icarus, 123, 56-62, 1996. Eshleman, Planet Space Sci., 21, 1521-1531, 1973.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.