1. Cassini
  2. Instruments and Data
  3. CIRS

About CIRS Data

1. Significant Updates.

  • In January 2010, we replaced version 1 of the CIRS data set (COCIRS_0nnn) with version 2.

  • In April 2010, we regenerated the entire reformatted CIRS dataset (COCIRS_5nnn) using the version 2 data.

The deliveries of version 1 were made quarterly over the span of several years. During that time the CIRS team made incremental adjustments in the calibration algorithm and calibration files used to prepare the volumes for delivery. The team redelivered the entire calibrated data set in December 2009 as version 2. All of the data in version 2 was calibrated with the same algorithm and set of calibration files.

In every regard, the new data files appear to be more reliable and better calibrated than the old.

With the improved calibration software, the team are better able to reject invalid spectra (which often occur while a shutter is opening or closing) and are better able to select the best calibration spectra to apply to any given observation. Consequently calibrated spectra pointed at deep space are now much closer to zero, and many anomalies and artifacts have disappeared. Another consequence is that there is not an exact one-to-one correspondence between files in version 1 and version 2.

  • In January 2011, the entire reformatted data set was regenerated again in order to clean up minor errors mostly relating to documentation. No significant changes were made to the data files which had been generated in or subsequent to the the major revision in April 2010. The January 2011 version is considered stable pending a follow-up review by the original peer review panel.

  • In July 2011, the CIRS team again redelivered their entire data set, this time as version 3.1. On line, we replaced version 2 of the CIRS data set with version 3.1.

    • The version 3.1 release incorporates a further refinement in the calibration algorithm.For interferograms collected using CIRS Flight Software Version 6 (executed in July of 2010), non-co-added data will have the 1/2 Hz noise spikes suppressed while no noise spike suppression will be done on co-added data.

    • In addition several changes to the contents of the data files were made. These changes necessitate modifications to our reformatting pipeline software which we are in the process of making.

  • In January 2015, the CIRS team again redelivered the Saturn encounter data (volumes COCIRS_0401 and higher); this time as version 3.2. On line, we replaced version 3.1 of the CIRS data set with version 3.2.

    • The version 3.2 release incorporates further refinements in the calibration algorithm and corrects some errors in that pipeline.

    • The version 3.2 release also includes new, highly derived products in the /DATA/CUBE directory tree of each volume.

  • In early May 2016, the CIRS team again redelivered the Saturn encounter data (volumes COCIRS_0401 and higher).

    • The primary data set, CO-S-CIRS-2/3/4-TSDR-V3.2 remains unchanged.

    • The data set of highly derived products, CO-S-CIRS-5-CUBES-V1.0, contains numerous corrections over the original delivery.

  • In April 2018, the CIRS team again redelivered the Saturn encounter data (volumes COCIRS_0401 and higher).

    • The primary data set, CO-S-CIRS-2/3/4-TSDR-V4.0, and the data set of highly derived products, CO-S-CIRS-5-CUBES-V2.0, reflect changes to several calibration routines.

    • For a complete list of changes in versions 2, 3 and 4, see the end of the DATASET.CAT file. Identical copies of this file are in the CATALOG directory of each volume.

  • In the meantime, the reformatted volumes remain based on version 2 of the data, and new volumes, beginning with COCIRS_1007, currently are available only in the original format.

2. Organization

  • The CIRS archive consists of three, multi-volume data sets. One data set covers the Jupiter encounter, and the other two span the entire Saturn portion of the mission. The two Saturn data sets contain exactly the same data in two different formats.

  • The archive volumes contain CIRS data products: raw data (interferograms) and calibrated data (spectra), with associated pointing, navigation and spacecraft orientation information, instrument documentation, calibration files, calibration algorithms, representative software for handling the CIRS data files, and documentation necessary to produce higher level calibrated products.

3. Documentation

Cassini CIRS Data User Guide.

  • The CIRS User Guide is available from the PDS Ring-Moon Systems Node holdings.

Users are strongly encouraged to review a CIRS aareadme.txt file. This file appears in the root directory of every volume. (Some of the header information in the aareadme.txt files varies from one volume to the next, but the body of information in the files is the same.)

Further details of the CIRS archive volumes and calibration procedures can be found in the DOCUMENT directory of each volume. However the bulk of this material has been consolidated in the Users Guide referenced above which should be considered the primary source for such information.

4. Data Formats

The CIRS data volumes delivered by the team involve variable length files in a rather complicated file structure. We are producing parallel volumes for the Saturn encounter containing re-formatted data and metadata designed to simplify access to the data. Consequently there are two data sets for the Saturn encounter easily distinguished by the first numerical digit in the volume IDs:

  • COCIRS_0nnn or COCIRS_1nnn indicate volumes in the original format.
  • COCIRS_5nnn or COCIRS_6nnn indicate the corresponding re-formatted volumes.

In the re-formatted version, the files have been converted from variable- length to fixed-length formats. ASCII versions of most binary files are also provided. In addition, file boundaries have been adjusted so that the data and metadata (timing and geometry information) associated with individual Cassini activities and with individual CIRS focal planes are found within a single set of files; no file contains information from more than one activity or one focal plane.

The following two links provide more detailed information on the current versions of the original and re-formatted data respectively.

  • Original Format - details and additional format specific documentation for the original structure.

  • Re-formatted - details and additional format specific documentation for the re-formatted structure.

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