About GCMS Data

1. Organization

• The GCMS archive consists of a single volume data set.


• The archive volume contains all testing and mission data from the GCMS instrument, covering the time period from May 1997 until Probe Entry in January 2005. It also includes post-mission processed data, extra files describing the processing parameters, and documentation.

2. Directory and File Naming

The GCMS archive data volume contains the following directories:

CATALOG - The catalog directory contains general information about the data set, including information about the instrument, personnel involved, and references.

• DATA - The data directory contains the instrument check-out data from GSFC and KSC (pre-launch), in-flight check-out data, and the descent data. It also contains the mole fraction data for methane, argon, and other species, which have been submitted to the DTWG team.


• DOCUMENT - The documentation directory contains important GCMS documents and the instrument health report. See below for more details.


• EXTRAS - The extras directory contains supplementary figures that explain the data processing algorithms and instrument housekeeping graphics for all check-out testing cycles.


• INDEX - The index directory contains the archive index for the entire data volume.

There is no software provided with the GCMS dataset. The data are in ASCII table format and are readable by a variety of plotting software packages.

The GCMS data files follow the naming conventions:

GCMS_DATATYPE_DESCRIPTOR_STAGE OF DATA PROCESSING.EXT

• The DATATYPE field refers to the source of the data or the scan type plus the instrument's operating mode.


• The DESCRIPTOR field contains different values depending on whether it refers to MS sweep data or Housekeeping data files.


• The STAGE OF DATA PROCESSING field refers to the level of data processing, and will be "STG1", "STG2" or "STG3".


• The EXT field is the file name extension, which describes what type of file it is.

More details about the file naming convention can be found in the EAICD (see below) or the DATASET.CAT file in the CATALOG directory.

3. Documentation

• Users are strongly encouraged to review the GCMS AAREADME.TXT file. This file appears in the root directory of the GCMS volume.


• Further details of the GCMS archive volume can be found in the "Experimenter to Archive Interface Control Document" (EACID) Document, which is found in the DOCUMENT directory on the data volume.


• A detailed description of the instrument can be found in the GCMS publications in Nature and ESA SP-1177, which are also in the DOCUMENT directory on the data volume.