Radio-Holographic Methods for Inversion of Radio Occultation Experiments of Past Venus' Spacecraft

We present the preliminary results of the ongoing efforts to reprocess radio occultation experiments of past NASA Venus' missions. For this purpose, we are implementing radio-holographic methods [1, 2] that make use of the complex radio signal during occultation to derive Venus' atmospheric profiles. These methods have been previously used in radio occultation experiments of the Earth's atmosphere (e.g., [3]). The main advantages of using this approach are the higher (sub-Fresnel) vertical resolution obtained, when compared to the traditional geometrical optics approach, and the possibility of resolving the signal when multi-path interference is present. As shown by [4], atmospheric profiles derived with radio-holographic methods can achieve vertical resolutions of ∼150m in height.

By reprocessing the multiple radio occultation sessions obtained by NASA's Pioneer Venus Orbiter (PVO) and Magellan spacecraft, we expect to improve the precision of the existing temperature profiles to enable the resolution of fine vertical structures. This is essential to investigate the role of local waves in the vertical transport of heat and mass, and the impact of these small-scale vertical motions in the global circulation of Venus' atmosphere. PVO gathered fourteen years (1978-1991) of radio occultation data covering altitudes from 38 - 100 km, day and night side, for both hemispheres. Magellan datasets span from October 1991 to October 1994, covering altitudes from 39 - 90 km, day and night side of the northern hemisphere. By reprocessing these datasets using radio-holographic methods we expect, in addition to an improved precision in the derived profiles, to enable the analysis of the temporal variation of the profiles with an extended coverage of spatial and solar illumination conditions (in combination with the results obtained by ESA's Venus Express and JAXA's Akatsuki orbiters).

[1] Jensen, A. S. et al. Radio Science, 38 (3), 2003.

[2] Jensen, A. S., et al. Radio science, 39 (3), 2004.

[3] Gorbunov, M. et al. Radio Science, 37 (5), 2002.

[4] Imamura T. et al. JGR: Planets, 123: 2151-2161, 2018.