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High-Resolution Data

in the Pioneer Venus Orbiter Ion Mass Spectrometer Level 1 Archive

Overview

The dataset has fixed length records. Each record represents one complete OIMS experiment data cycle (normally 6.3 seconds but this time can vary with the bit rate). Within each record there are 55 samples of mass and 55 samples of densities associated with those masses. The sequence of masses within a record normally will follow the OIMS "explore" mode, but this sequence will vary when the experiment occasionally is in the "explore-adapt" mode.

To compute the time associated with a particular mass and density, the dwell time should be used, along with the time of day. The dwell time is the time interval (milliseconds) between samples. Thus, for the "nth" sample, the time (in seconds) would be computed as follows:

The user should be aware that some of the data values have been coded. For example, a density of 9.9999e+04 indicates that a density could not be computed for that point. (This can be due to several reasons, such as telemetry interference or occurrence of a gap in data.) Also, a negative value of density represents a "flagged" data point and should be used with caution. Other flag values are described by the MISSING_CONSTANT lines in the format files (*.FMT) accompanying the data.

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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 high-resolution data users.

• The high-resolution dataset is described in the file HI_RESDS.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 high-resolution data are provided as ASCII tables, with one table file (*.TAB) per orbit. These files reside under the /DATA/HIGH_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 high-resolution files. This format also is described in the PDS format file OIMSDATA.FMT found in each 100-orbit subdirectory 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 mass and 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 high-resolution data files on this disk.

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

The directory /DATA/HIGH_RES/ORBnnnn, where nnnn is a numeral, is the 100-orbit subdirectory containing the hundred orbits starting with nnnn. For example, /DATA/HIGH_RES/ORB3600 holds data from orbits 3600 through 3661.

The file ORBnnnn.TAB, where nnnn is a numeral, contains the data from orbit nnnn. For example, ORB3661.TAB contains the data from orbit 3661 (and thus is found in directory /DATA/HIGH_RES/ORB3600).

ORBnnnn.LBL is the name of the PDS label file which describes the data file ORBnnnn.TAB. Example: ORB3661.LBL describes ORB3661.TAB. Such label files provide descriptive information in a format which is both human-readable and machine-readable.

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