About Re-formatted CIRS Data
These pages contain excerpts from the TUTORIAL.TXT file, found in the DOCUMENT directory on each re-formatted volume. See TUTORIAL.TXT for extensive guidance on how to use the data.
1. Overview of the Re-Formatted Data Set
This data set has been designed to ease the access to the CIRS data set for scientists who do not use Vanilla. It simplifies the selection of data subsets based on target, CIMS request or CIRS focal plane. The reorganization also eliminates the need for variable-length files, on the assumption that users will have a much easier time writing programs to read fixed-length records.
The re-formatted data set has the following properties.
(a) File boundaries correspond to CIMS requests, so the data associated with individual Cassini activities are found within a single set of files; no file contains information from more than one CIMS activity.
(b) Data files have been divided up by focal plane.
(c) Metadata files (mainly timing and geometry) have been restructured to contain the identical record sequence as that in the corresponding data files. Users will find an exact 1:1 correspondence between the records in each data file and the records in the metadata files.
(d) All information except the actual thermal spectra are available in ASCII format. Most users find ASCII files easier to read than binary files. However, because the spectra are quite large, they are only archived in binary.
2. Volume Names
The original CIRS data volumes are named COCIRS_yymm, where yy is the last two digits of the year and mm is the month number (01 through 12).
These re-formatted volumes are also organized by month. To distinguish the two data sets, re-formatted volumes have 50 added to the year. For example, the data in original volume COCIRS_0407 can be found, in the alternative form, in volume COCIRS_5407.
3. Introduction to the Cassini Timeline
The Cassini timeline has been allocated in terms of specific activities, sometimes referred to as “CIMS requests.” Here “CIMS” stands for the “Cassini Information Management System.” A CIMS request corresponds to a particular block of time in which one or more instruments observe (usually) a single target. In the Cassini timeline, one instrument is always “prime” and defines the details of the observation, such as where the instrument points and how long it dwells at each location. Often, additional instruments are “riders” and will obtain simultaneous data from the same target.
CIMS requests have identifiers such as this:
CIRS_016RE_E60PHASE001_VIMS
It is constructed as follows:
CIRS: Indicates the instrument doing the observation, regardless of whether it is prime or a rider.
016: Indicates Cassini’s orbit number
RE: Abbreviation for the nominal target, in this case Ring E.
E60PHASE: A brief mnemonic indicating the purpose of the observation, in this case to gather the phase curve information around 60 degrees.
001: For the first activity of this type in the given orbit of Cassini.
VIMS: Finally, this indicates that the VIMS (Visual and Infrared Mapping Spectrometer) instrument is prime for the observation. If CIRS had been prime, the identifier would have ended with PRIME instead.
The CIMS request ID associated with a given file can be found in the PDS label as the value for the keyword OBSERVATION_ID.
4. Where to go next
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Use the tabs at the top of this page to obtain more information about the re-formatted data.
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