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Radio Occultation (ORO)

NSSDCA ID: 1978-051A-20

Mission Name: Pioneer Venus Orbiter
Principal Investigator:Dr. Arvydas J. Kliore

Description

The Orbiter Radio Occultation (ORO) experiment made use of the S-band and X-band radio signals for data measurements. The objectives were (1) to measure refractivity profiles, (2) to measure S- and X-band dispersion and absorption, (3) to measure electron density height profiles, and (4) to determine the dynamics of the lower atmosphere.

The ORO experiment worked by observing X and S band radio transmissions passing through the ionosphere and atmosphere of Venus on their way to Earth. The changes in the phase and amplitude of the signals at Earth provided information on the refractive index and absorptivity profiles of the atmospheric regions they passed through. The geometry of the orbit had to be such that the line of sight (including the "bend" due to atmospheric refraction) between the spacecraft and Earth would pass through the Venus atmosphere. This happened about 80 times in the nominal mission, yielding 160 profiles (one each for X ans S band). The method worked for the atmosphere above about 34 km. Below this altitude, the radio waves were refracted so as to hit the surface and not reach Earth.

The electron density distribution can also be measured using the dispersive differential Doppler effect on the two frequencies, giving data on the Venus ionosphere. Amplitude fluctuation of S and X band signals can provide information on the radio absorption structure of the clouds. The Deep Space Network stations were equipped with receivers capable of varying their reference frequency by means of programmable oscillators.

Pioneer Venus Orbiter Radio System

1.09 m diameter high-gain parabolic dish antenna mounted on a 2.9 meter mast on the top deck of the spacecraft. It is despun from the rotating spacecraft so that it always faces Earth. It is also capable of being pointed up to 15 degrees from the Earth during Venus atmospheric occultations, to account for the refraction of the beam as it passed through the atmosphere. It operated in both S and X bands. At S-band, the antenna beam is 7.6 degrees. The orbiter carries a 750 mW X band (8.415 GHz) transmitter and a 2.295 GHz S band transmitter. The frequencies are set so that the X-band frequency is 11/3 of the S band.

Alternate Names

  • ORO
  • PioneerVenusOrbiter/ORO
  • urn:nasa:pds:context:instrument:pvo.orse
  • urn:nasa:pds:context:instrument:rss.p12

Discipline

  • Planetary Science: Atmospheres

Additional Information

Questions and comments about this experiment can be directed to: Dr. Dieter K. Bilitza

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Arvydas J. KliorePrincipal InvestigatorNASA Jet Propulsion Laboratoryarvydas.j.kliore@nasa.gov

Selected References

  • Berman, A. L., and R. Ramos, Pioneer Venus occulation radio science data generation, IEEE Trans. Geosci. Rem. Sens., GE-18, No. 1, 11-14, doi:10.1109/TGRS.1980.350252, Jan. 1980.
  • Kliore, A. J., et al., The polar ionosphere of Venus near the terminator from early Pioneer Venus Orbiter radio occultations, Science, 203, No. 4382, 765-768, doi:10.1126/science.203.4382.765, Feb. 1979.
  • Kliore, A. J., et al., Initial observations of the nightside ionosphere of Venus from Pioneer Venus Orbiter radio occultations, Science, 205, No. 4401, 99-102, doi:10.1126/science.205.4401.99, July 1979.
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