Version 1.0 of the PVO Cruise Data Set

The Pioneer Venus Orbiter (PVO) data sets consists of three types of data:

  1.  'Merged EDR' data
  2.  'Spectral' data
  3.  'Summary' (high resolution) and
  4.  Hourly averaged solar wind parameter data, along with associated
  5.  Trajectory data.

Plasma parameters were derived from a least squares fit of a convected
Maxwellian to solar wind spectra from the PVO Plasma Analyzers. As with the
Pioneer 10 and 11 analysis, these fits are roughly analogous to the 'fit'
parameters from the Voyager spacecraft. For technical reasons related to the
greater width of the spectra at the heliocentric distance of PVO (0.72 AU),
this analysis has not been as thoroughly tested as the analysis for Pioneers 10
and 11 plasma parameters. Still, velocities from PVO seem to be quite accurate.
The relative accuracy of the densities and temperatures should also be high
(20%?), though the absolute accuracy of the density measurements remains to be
determined.

Format

These files are written as ASCII in an 80-column format for ease of
translation. Each file contains a header followed by data records. Each data
record contains the spacecraft ID (SCID), year, day of year, and time of day in
hours, followed by the bulk velocity, number density, temperature, and where
appropriate, the flow angles.

Co-ordinate systems and units

Speeds are given in km/s, number densities are given in #/cc, temperatures are
given in K, and flow angles are given in degrees. All directions are given in
an RTN co-ordinate system , in which the E/W angle is positive in the direction
of planetary rotation while a N/S angle of zero that the solar wind flow is
radial.

Uncertainties

Tests with simulated spectra suggest the uncertainties in the parameters are
comparable to the uncertainties in measurements from Pioneers 10 and 11:

Parameter     Uncertainty
_________________________________________________________________

V             3-5 km/s

N             Internally consistent to 20%.  Simulations also
              suggest an absolute accuraty of 20%, but N seems to
              be 50% higher than comparable measurements from
              Voyager 2.

T             20% for T > 10,000 K

Flow Angles   Accuracy remains to be determined.  In particular,
              systematic errors in the correction for spacecraft
              attitude may have intoduced a slight offset.

Merged EDR data

Merged EDR (Experiment Data Record) data is a low-level product, very close to
raw telemetry, that contains segments of data from the plasma analyzers
interlaced with engineering data. This data is stored at Ames for production
purposes. Because it can only be read with specialized software there is no
plan to make this data available for general distribution. All the information
it contains is available in the 'spectral data' descibed below.

Spectral data

The spectral data set contains spectra from the PVO plasma analyzer, along with
associated engineering data, in a compact and easily read format. Every
spectrum has been stored; no attempt has been made to 'filter out' noise, bad,
or partial spectra. Because it reflects the full resolution of the plasma
analyzer (approximately 1 spectrum ever 13 minutes) this may be the preferred
data set for use in detailed studies of waves and discontinuities, as well as
the microscopic physics of the solar wind, but it must be used with caution.
Due to its size, this data set is stored offline. There are also plans to
transfer this data to the Planetary Data System PDS). For more information,
contact Paul R. Gazis

Summary (High Resolution) Data Set

[Image] NOTE: This data has not yet been installed on this system! If you
require high-resolution data, you should contact Paul R. Gazis

The summary data set contains individual fits to valid solar wind spectra from
the plasma analyzers. Velocities have been corrected for abberation due to the
motion of the spacecraft and all times are in spacecraft event time (SCET).
Every valid spectrum has been processed so this data set reflects the full
resolution of the plasma analyzer.

Hourly Averaged Data Set

Hourly averaged data files were created by averaging every valid parameter in
each hour. This is the preferred data set for most studies of the solar wind.

Trajectory Data

WARNING: These trajectory data are only approximate! They were derived by
extrapolating data from a single point in the middle of the cruise phase of the
mission back to launch and forward to Venus and are not guaranteed to be
accurate to better than 100,000 km near the beginning and end of the cruise
phase. This trajectory will be improved in the future.

These files are written in ASCII in an 80-column format for ease of
translation. Each file contains a header followed by a succession of data
records. Each data record contains the spacecraft ID (SCID), year, day of year,
and time of day in hours, followed by the Cartesian state of the spacecraft in
ecliptic co-ordinates, where the x-axis is directed towards the first point in
Ares while the z-axis points north.

For more information, contact:

Dr. Paul R. Gazis, SJSU Research Associate

phone: (415) 604-5704
fax:   (415) 604-6779
email: gazis@arwen.arc.nasa.gov

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last modified 28 July 1995.