Analysis of NASA's DSN Venus Express radio occultation data for year 2014

Abstract

The Venus Express Radio Science Experiment (VeRa) was part of the scientific payload of the Venus Express (VEX) spacecraft and was targeted at the investigation of Venus' atmosphere, surface, and gravity field as well as the interplanetary medium. This paper describes the methods and the required calibrations applied to VEX-VeRa raw radio occultation selected data used to retrieve vertical profiles of Venus' ionosphere and neutral atmosphere. In this work we perform an independent analysis of a set of 25 VEX, single-frequency (X-band), occultations carried out in 2014, recorded in open-loop at the NASA Deep Space Network. The calibrations are performed to correct the observed frequency for the major noise sources and errors, since any uncalibrated effects will bias the retrieval of atmospheric properties. We present a study on the influence of the relativistic effects on radio occultation of Venus. The temperature differences between the relativistic and non-relativistic Doppler shift solutions are lower than 0.5 K at 50 km altitude, and our error analysis shows that, within this investigation, the relativity effects can safely be neglected. Our temperature, pressure and electron density vertical profiles are in agreement with previous studies available in the literature. Furthermore, our analysis shows that Venus' ionosphere is more influenced by the day/night condition than the latitude variations, while the neutral atmosphere experiences the opposite. Our scientific interpretation of these results is based on two major responsible effects: Venus' high thermal inertia and the zonal winds. Their presence within Venus' neutral atmosphere determine why in these regions a latitude dependence is predominant on the day/night condition. On the contrary, at higher altitudes the two aforementioned effects are less important or null, and

Determination of uncertainty profiles in neutral atmospheric properties measured by radio occultation experiments

“…The frequency shift is modeled from the ephemerides of the spacecraft and planets, and these are given by NASA's SPICE toolkit Navigation and Ancillary Information Facility (NAIF) [33]. Then, the physical properties (e.g., the neutral number density, the pressure, and the temperature) can be inferred by making use of the ideal gas law together with hydrostatic equilibrium assumption (see e.g., Schinder et al [9] for Titan, Fjeldbo and Eshleman [5] for Mars, and Fjeldbo et al [14], Gramigna et al [34] for Venus). Therefore, the profiles φ(K), N (K), P (K), and T (K) that are needed for evaluating our analytical solutions in Eqs.…”