Low-Resolution Data

in the Pioneer Venus Orbiter Ion Mass Spectrometer Level 1 Archive

Overview

This dataset was provided by the principal investigators to the National Space Science Data Center. The data are from the first 2997 orbits of the Pioneer Venus Orbiter. (Not all of these orbits are included on the present disk volume.) Each data record includes the year and day of year; time (second of day); orbit number; time tag (from -1800 to +1800 in increments of 12); and the number densities (number per cc) of 12 individual positive ion species (O, O2, NO CO2, C, N, H, He, atomic oxygen 18, O2, CO, and N2). The values are derived by averaging of all measurements within the 12s of each UADS sample time. Possible error sources are described in the documentation.

The values -9999.999 in the seconds-after-periapsis column, and -999999 in the density column, signify flagged (invalid or missing) data values.

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Documents

This disk contains documentation files which describe the datasets on the disk, the instruments from which the data came, and the Pioneer Venus Orbiter spacecraft and mission. These files are found in the CATALOG and DOCUMENT directories.

The following files in CATALOG are of particular interest to low-resolution data users.

• The low-resolution dataset is described in the file 12SDS.CAT.
• The Orbiter Ion Mass Spectrometer instrument is described in the file OIMSINST.CAT.
• The Pioneer Venus Orbiter spacecraft is described in the file PVO_HOST.CAT.
• The Pioneer Venus Orbiter mission is described in the file MISSION.CAT.
• A list of literature references relevant to the Orbiter Ion Mass Spectrometer is found in REF.CAT

The DOCUMENT directory contains a variety of documents which may be helpful to the users of the low-resolution data.

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File Formats

The files on this disk are in level 1 compliance with the ISO 9660 standard. The low-resolution data are provided as ASCII tables, with one table file (*.TAB) per orbit. These files reside under the /DATA/LOW_RES directory on this disk, where they are organized into 100-orbit subdirectories.

What follows is a very brief summary of the format of the data in the low-resolution files. This format also is described in the PDS format file OIMSDATA.FMT found in each 100-orbit subdirectories of low-resolution data. This format file is both human-readable and machine-readable.

The beginnings of two lines of data, with headings added, as an example of this format:

(Note: these data may be displayed with spacing different from that of the actual data. Each data line ends with two ASCII record delimiter characters, carriage return and line feed. The density columns omitted here are formatted the same as the ones shown.)

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Links to Data Files

The following links can be used to navigate the low-resolution data files on this disk.

The file naming convention for these data files is as follows:

The directory /DATA/LOW_RES/ORBnnnn, where nnnn is a numeral, is the 100-orbit subdirectory containing the hundred orbits starting with nnnn. For example, /DATA/LOW_RES/ORB0900 holds data from orbits 900 through 999. (Exception: /DATA/LOW_RES/ORB0001 has orbits 1-99.)

The file ORBnnnn.TAB, where nnnn is a numeral, contains the data from orbit nnnn. For example, ORB0905.TAB contains the data from orbit 905 (and thus is found in directory /DATA/LOW_RES/ORB0900).

ORBnnnn.LBL is the name of the PDS label file which describes the data file ORBnnnn.TAB. Example: ORB0905.LBL describes ORB0905.TAB. Such label files provide descriptive information in a format which is both human-readable and machine-readable.

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