Structure and dynamics of the Venus Neutral Atmosphere: The Venus Express Radio-Science Experiment
- Paper number
IAC-09.A3.6.3
- Author
Ms. Alice Verweyen, Imperial College London, United Kingdom
- Coauthor
Dr. Silvia Tellmann, Rheinisches Institut für Umweltforschung, Germany
- Coauthor
Dr. Martin Paetzold, Rheinisches Institut für Umweltforschung, Germany
- Coauthor
Prof. Bernd Haeusler, Institut für Raumfahrttechnik Universität der Bundeswehr München, Germany
- Coauthor
Dr. Michael Bird, Argelander-Institut für Astronomie, Germany
- Year
2009
- Abstract
Venus Express, ESA’s first spacecraft to our nearest neighbour planet, was launched in November 2005 and began orbiting Venus in April 2006. Among the seven investigations included in the payload, the Venus Express Radio Science Experiment (VeRa) utilizes the spacecraft’s carrier signals at S-band and X-band to probe the Venus neutral atmosphere and its ionosphere. The spacecraft transmits to Earth during periods of occultation when the radio signals traverse the Venus atmosphere - a geometric configuration that occurs twice during each experiment (occultation ingress and egress). By analysing the influence of the atmosphere on the signal, conclusions can be drawn about its structure. The polar orbit of Venus Express is especially well suited for sounding the Venus atmosphere over a large range of planetocentric latitudes and local times. The onboard frequency reference source for this dual- frequency one-way radio link is provided by an Ultrastable Oscillator (USO). Ground stations on Earth record the amplitude, phase and polarization of the received occulted signal. Simultaneous coherent measurements at two different wavelengths enable one to separate the signature of the neutral atmosphere from the dispersive effect of the ionosphere. Using this occultation technique, it is possible to sound the Venus atmosphere down to altitudes well below the cloud deck at 55-60 km altitude. Observations of the first three Venus Express occultation seasons are used to retrieve refractivity profiles at altitudes between 45 km and 350 km. Ionospheric electron density profiles are reconstructed by using the X-Band, S-Band and differential S/X-Band data at heights above 100 km. Number density, temperature, and pressure profiles of the neutral atmosphere are obtained from the X-Band data in the altitude range 45-100 km. Zonal wind maps of the neutral atmosphere are derived from the temperatures using the thermal wind equation. The measured mesospheric and lower thermospheric densities and temperatures are compared to empirical models. Day-night variations of the atmospheric structure and dynamics, as well as salient features like the cold collar region, are investigated for each occultation season.
- Abstract document
- Manuscript document
(absent)