Version 1.0 of the Pioneer Venus Orbiter Data Set The Pioneer Venus Orbiter (PVO) data sets contain five types of data: 1. 'Merged EDR' data 2. 'Spectral' data 3. 'Summary' (high resolution) parameter data 4. Hourly averaged parameter data 5. PVO orbital parameters. The plasma parameters involve least squares fit of a convected Maxwellian to the solar wind spectra from the Plasma Analyzers aboard the PVO spacecraft. As with the Pioneer 10 and 11 data analysis, these fits are roughly analogous to the 'fit' parameters from the Voyager spacecraft. For reasons related to the greater width of the spectra at the heliocentric distance of PVO (0.72 AU), the PVO data analysis has not been as thoroughly tested as the analysis for Pioneers 10 and 11 plasma parameters. Still, velocities from PVO should be quite accurate. The relative accuracy of the densities and temperatures should also be high (20%?), although the absolute accuracy of the density measurements remains to be determined. Format 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. Data records contain the spacecraft ID (SCID), year, day of year, and time of day in hours, followed by the bulk velocity, number density, temperature, and 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 a spacecraft-centered ecliptic system, in which the E/W angle is positive in the direction of planetary rotation while a N/S angle of zero means that the solar wind flow is parallel to the plane of the ecliptic. NOTE: unless the spacecraft is in the plane of the ecliptic, this is different from an RTN system, in which a N/S angle of zero means 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. There may also be an offset due to a slight systematic error in corrections for the attitude of the spacecraft. 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 of 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 micrscopic 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. For more information, contact Paul R. Gazis Summary (High Resolution) Data Set [Image] NOTE: Due to space limitations, 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. Measurements made inside the Venusian bow shock were excluded except in a few instances. These instances are identified by an SCID of 'PVOS' rather than 'PVO ' and should be discarded! Some of this data was taken inside the Venusian bow shock. This data is less reliable, was only included for the sake of completeness, and should be discarded. It is indicated by an SCID of 'PVOS' rather than 'PVO '. Orbital Parameters The orbital parameter file contains the parameters for each succesive orbit of the PVO spacecraft. It is written in ASCII in an 80-column format for ease. It consists of a header followed by syuccessive records that should be self-explanatory. Most of these parameters were obtained from microfilm records or SEDR tapes, but for some orbits the parameters were interpolated. Those orbits are identified by negative orbit numbers. 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 ------------------------------------------------------------------------------- [Go to] Parent Directory [Go to] ARC Pioneer Plasma Group Home Page last modified 28 July 1995.