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Pioneer Venus Special Events Data (SED)


Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)

Time span: 1978-12-05 to 1981-10-21


This collection consists of the Special Events Data (SED) produced by the Unified Abstract Data System (UADS). The data were originally submitted as EBCDIC records produced on an IBM 360 computer. They were translated into ASCII stream data without any control characters for line endings (e.g, no \r and no \n) by NSSDC.

The data span several separate files for a number of instruments on the Pioneer Venus orbiter as well as the four atmospheric probes. Descriptions of the details and formats of the different data are available in some cases as files as well as on external documentation. Short descriptions of the data follow.

Solar Wind Plasma Analyzer: Date/Velocity Data

These data consist of reduced solar wind flow speed (km/s) and proton number density (per cc) observed just before the (first) inbound crossing of the bow shock of Venus, and the same quantities just after the (last) outbound crossing. Those parameters were obtained by a least squares fit of a convecting isotropic Maxwellian proton velocity distribution, convolved through the instrument response function obtained from laboratory calibration, to the raw currents. The flow speed obtained by this procedure should normally be accurate (conservative error bars would be +/-10%). The proton number density is generally less accurate (conservatively +/-50%). Each file on tape contains data for 31 orbits. Orbit number, times of measurement (hours and minutes UT at the spacecraft), and reduced parameters are given for each orbit. The precise time of measurement refers to the completion of the measurement cycle (approximately 9 minutes) of 45 spin periods. The time is always within two measurement cycles of the inferred shock crossing. These data cover the time period from 05 December 1978 to 21 October 1981 (Orbits 1-740) and span 35 files.

Pioneer Venus Atmospheric Drag Model

Each record contains the local solar time in hours; altitude (km); density (g/cc); number density of atomic oxygen (part/cc); ratio of number densities of O/CO2; and temperature. The data are contained in one file.

Atmospheric Drag Observations

Each record consists of time in month, day of month, and year; orbit number; altitude (km); density (g/cc); error in density/density; scale height (km); exospheric temperature; local solar time in hours; and Venus longitude. The data are contained in one file and cover the time period 09 December 1978 to 07 August 1979 (Orbits 5-246).

Atmospheric Structure: Pressure and Temperature

Each record consists of Ground Received Time (GRT) in hours, minutes, and seconds; derived altitude (km); atmospheric pressures, temperatures, and derived densities; and compressibility factor. The pressure data tabulated have been corrected for offsets and sensor non-linearities, and for Probe dynamic pressure due to the velocity of descent. The temperature data have been corrected for zero offset, for amplifier drift, and for dynamic temperature effects due to Probe velocity. Compressibility factors range from 0.999 at the highest altitudes to a minimum of 0.9925 around 25 km to a maximum of 1.009 at the surface. Altitudes are referenced to 6052.0 km, which is the observed radius in the vicinity of the Large Probe landing site as determined by the Orbiter Radar Altimeter Experiment. The data are based on the merging of two independent sets of data from redundant sensors.

For the Large Probe, data entries are at 4-s intervals above 13 km, and at 32-s intervals thereafter. For the small probes, data intervals are 8 s in upper descent, 16 s in lower descent, and 32 s below 12-14 km. Below about 13 km the temperature data were faulty, so in this region extrapolated values are given. These data are available for the date of entry of the probes (09 December 1978).

Nephelometer Data

Three kinds of data from the nephelometer experiment are included: (1) backscatter channel data; (2) ambient background radiation channels and spectral functions; and, (3) time vs. temperature. The data for each probe are combined into one file for a total of four files.

The backscatter channel data consist first of a tabulation of the angular weighting or sensitivity function, f (theta), for the nephelometer as a function of scattering angle with respect to the direction of propagation of a nearby monochromatic incident light beam at a wavelength of approximately 900 nanometers. The next section contains the actual measured cross sections as a function of Ground Received Time (GRT). The data include the data baseline offsets in order to illustrate the fluctuation of the data and give some indication of baseline drift during the descent of the Probe. It is necessary to subtract these baseline offsets from the data in order to obtain the true cross section. The first data listed are readings of a monitoring target placed in the field of view (FOV) of the instrument. This target was automatically removed from the FOV upon instrument deployment as noted by the comment "aeroshell removed" (or, in the case of the small probes, "window cover open").

The ambient background radiation channels and spectral functions data are provided only for the small probes. The data consist first of tabulations of spectral functions vs. wavelength in nanometers for the UV and visible channels. The second portion of data consists of the instrument readings along with the Ground Received Time (GRT). The time of window cover opening is noted. For these data, the baseline offset has not been subtracted from the data presented so that the user may attempt to note small deviations from the baseline. Baseline offset values are about those values recorded by the instrument prior to window cover opening. All the data received from the probes were tabulated from instrumental deployment until instrument or probe failure occurred.

The time vs. temperature data are also provided only for the small probes. The data consist of a listing of the instrument temperatures at the locations of the light-emitting diode (LED) vs Ground Received Time (GRT). These data are provided to indicate the range of internal environmental conditions experienced by the instrument.

Gas Chromatograph: Lower Atmosphere Composition

These data consist of one file which contains the Ground Received Time (GRT) in hours, minutes, and seconds; altitude (km); atmospheric pressure (bars); concentration and intervals for the following gases: CO2, N, H2O, O, Ar, CO, Ne, and SO2; and the upper limits for the following undetected gases: H, CH4, Kr, ethylene, ethane, hydrogen sulfide, carbonyl sulfide, propane, and nitrous oxide. Carbon dioxide and the seven neutral minor constituents were determined from individual and direct measurement of peak areas by computerized curve fitting.

Net Flux Radiometer

These data consist of four files, one describing the data and one each for data from the small probes. The data files contain the Ground Received Time (GRT) in minutes after 1900 GMT; altitude (km) above 90.3 bars surface pressure; pressure (bars); atmospheric temperature (K); external sensor temperature (K); net total radiance flux density in watts/sq m as measured, with positive signs indicating upward flux exceeds downward flux; and net flux corrected for estimated effects of deployment transient, rate of change of offset, and non-vertical attitude.

Infrared Radiometer

The data consist of pre-entry, descent, and on-board calibration data from the infrared radiometer on the Large Probe. The data contain Ground Received Time (GRT) in hours, minutes, and seconds; flux measurements (in watts per square meter) for the following micrometer spectral bandpasses: 3-160, 6-7, 7-8, and 8-9. The on-board calibration data indicate an increasing signal during the descent phase of the mission. This was due to increasing probe bus voltage; the calibration system was not on regular power. This type of change was observed during calibration of the instrument. The last calibration cycle ended 2minutes, 18 seconds prior to impact on Venus' surface.

Solar Flux Radiometer

These data contain Ground Received Time (GRT) corresponding to when the data sample was taken; atmospheric pressure in earth atmospheres; altitude (km); the upward, downward, and net (downward minus upward) flux in the visible channel (approximately 0.40-0.96 microns); the upward, downward, and net fluxes for the narrow-band channel (approximately 0.59-0.67 microns); and the upward, downward, and combined fluxes for the combined channel (a synthesis of both the visible and infrared channels into a single broad-band (approximately 0.41-1.78 microns).

Alternate Names

  • PV Special Events Data (SED)


  • Planetary Science: Atmospheres


  • 78-051A-18A
  • 78-051A-19B
  • 78-051A-19C
  • 78-078D-01A
  • 78-078D-02A
  • 78-078D-04A
  • 78-078D-05A
  • 78-078D-07A
  • 78-078E-01A
  • 78-078E-02A
  • 78-078E-02B
  • 78-078E-02C
  • 78-078E-04A
  • 78-078F-01A
  • 78-078F-02A
  • 78-078F-02B
  • 78-078F-02C
  • 78-078F-04A
  • 78-078G-01A
  • 78-078G-02A
  • 78-078G-02B
  • 78-078G-02C
  • 78-078G-04A

Additional Information



Questions and comments about this data collection can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. Alvin SeiffData ProviderNASA Ames Research Center
Dr. Verner E. SuomiData ProviderUniversity of Wisconsin-Madison
Dr. Aaron BarnesData ProviderNASA Ames Research Center
Dr. Gerald M. KeatingData ProviderNASA Langley Research Center
Dr. Martin G. TomaskoData ProviderUniversity of
Prof. Jacques E. BlamontData ProviderCNRS, Service d'Aeronomie
Dr. Boris RagentData ProviderNASA Ames Research Center
Mr. Vance I. OyamaData ProviderNASA Ames Research Center
Dr. Robert W. BoeseData ProviderNASA Ames Research Center
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