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Differential Long Baseline Interferometer (DLBI)

NSSDCA ID: 1978-078E-03

Mission Name: Pioneer Venus Small Probe (North)
Principal Investigator:Dr. Charles C. Counselman


This experiment involved applying differential long-baseline interferometry techniques to the radio signals from the entry probes and bus in order to infer or place upper limits on wind speeds in the lower atmosphere. These results were used in modeling the circulation patterns of Venus' atmosphere.

As the four probes descended, the Pioneer Venus Probe Bus followed a well-defined ballistic trajectory above the atmosphere that was accurately known with respect to the planet's surface. Probe velocities were measured relative to the Bus. Additionally, four ground stations on Earth simultaneously tracked the four probes. These were the 64-meter dish Goldstone and Canberra Deep Space Network (DSN) stations, and the 9-meter dish Santiago (Chile) and Guam Spaceflight Tracking And Data Network (STDN) stations. They covered passbands of 2291 to 2293 MHz to receive signals from all four probes and the bus simultaneously. The Doppler frequency shifts of the received 13 cm (S-band) signals gave the component of the velocity vector along the Earth-spacecraft line of sight. The differential long-baseline interferometry was used to find the other two components of the velocity vector of each probe.

Measurements of the temperature and pressure taken by other instruments as the probes descended were used with the interferometry results. Data taken prior to probe entry were used, where feasible, to infer characteristics of Venus' gravity field for use with probe entry operations as well as in later scientific evaluation. Deviations of the probe trajectories from the mathematical model of their trajectories in a still atmosphere were attributed to winds. Overall uncertainties were estimated at 10 cm/s.

The magnitude of the wind velocity was found to be about 1 meter/s or less near the surface of the planet and about 100 meters/s near 65-km altitude at all four probe locations. High wind shear was measured centered at altitudes of 15, 45, and 60 km. The wind velocity was uniformly directed very close to due west, except within a few km of the surface.

Alternate Names

  • DLBI
  • PioneerVenusSmallProbeNorth/DLBI

Funding Agency

  • NASA-Office of Space Science (United States)


  • Planetary Science: Atmospheres

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. Irwin I. ShapiroOther InvestigatorMassachusetts Institute of
Prof. Jule CharneyOther InvestigatorMassachusetts Institute of Technology
Dr. Gordon H. PettengillOther InvestigatorMassachusetts Institute of
Dr. Ronald G. PrinnOther InvestigatorMassachusetts Institute of
Dr. Charles C. CounselmanPrincipal InvestigatorMassachusetts Institute of

Selected References

  • Counselman, C. C., III, et al., Wind velocities on Venus: Vector determination by radio interferometry, Science, 203, No. 4382, 805-806, doi:10.1126/science.203.4382.805, Feb. 1979.
  • Counselman, C. C., III, et al., Zonal and meridional circulation of the lower atmosphere of Venus determined by radio interferometry, J. Geophys. Res., 85, No. A13, 8026-8031, doi:10.1029/JA085iA13p08026, Dec. 1980.
  • Colin, L., Ed., and D. M., Ed. Hunten, Pioneer Venus experiment descriptions, Space Sci. Rev., 20, No. 4, 451-525, doi:10.1007/BF02186463, June 1977.
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