Remote sensing of the turbulence characteristics of a planetary atmosphere by radio occultation of a space probe

Authors

  • Richard Woo,

  • Akira Ishimaru


Abstract

The purpose of this paper is to analyze the effects of small-scale turbulence on radio waves propagating through a planetary atmosphere. The analysis provides a technique for inferring the turbulence characteristics of a planetary atmosphere from the radio signals received from a spacecraft as it is occulted by the planet. The planetary turbulence is assumed to be localized and smoothly varying with the structure constant varying exponentially with altitude. Rytov's method is used to derive the variance of log-amplitude and phase fluctuations of a wave propagating through the atmosphere. When the distance between the spacecraft and the planetary atmosphere exceeds L02/λ, where L0 is the outer scale of turbulence, the effects of inhomogeneity and finite size of the turbulent medium become important. A recent study by Gurvich [1969] pointed out that the structure constant for the Venusian atmosphere inferred from the Mariner-5 occultation data was significantly lower than that inferred from the Venera-4 data. By applying the analysis developed in this paper it is shown that the effects of inhomogeneity and finite size of the turbulence, which were excluded in Gurvich's analysis, account for this difference. More important, however, is the fact that the new techniques are available for use in future radio-occultation missions.

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