1. Cassini
  2. Instruments and Data
  3. CIRS

** Users are strongly encouraged to review a CIRS aareadme.txt file.** This file appears in the root directory of every volume.

1. Introduction to CIRS Data

For full details about the CIRS instrument, see COCIRS_0xxx/COCIRS_0xxx/CATALOG/INST.CAT: an INST.CAT file.

The CIRS instrument has several unusual properties, which have made the CIRS data particularly challenging to work with:

(a) The instrument has variable resolution, which means that the number of samples in a spectrum varies from one observation to the next, and sometimes within a single observation.

(b) The instrument has three focal planes, referred to as FP1, FP3 and FP4. (FP2 was eliminated in a descope). Because the three focal planes typically operate simultaneously, a single observation from the instrument can generate spectra covering several different ranges of wavenumber.

(c) A great deal of processing is required to go from the raw interferograms to the calibrated CIRS spectra that a typical user requires. For this reason, the CIRS team has kindly archived calibrated data (called apodized spectra) in addition to the raw data. (Note that the calibration procedure is continuing to evolve; if you want the latest, most reliable calibration of a spectrum, it would be best to contact a member of the CIRS team.)

(d) Although FP1 has a single circular field of view, FP3 and FP4 each consist of ten square pixels, of which five can be read out at a given time. Each pixel captures a different region of a target, and sometimes a different target. For this reason, the CIRS team has archived extensive tables of geometric metadata along with each spectrum, describing the instantaneous field of view of each pixel.

To solve the problems of working with this complicated data set, the CIRS team has developed a software package called Vanilla, and has archived the data in a format that is closely tied to the software. For example, because the spectra have different lengths, the CIRS team has adopted a binary, variable- length record format, combined with an index that describes where to find a particular spectrum within the larger data file. In addition, data from the different focal planes are interspersed within the same file. Data files themselves are organized simply by time, where a single file contains every spectrum obtained within a single interval, typically lasting 8 hours.

The Vanilla software makes it relatively easy for users to retrieve a desired selection of spectra from these files. However, those who do not use Vanilla might find it difficult to access the CIRS data in the original format. Consequently, the Ring-Moon Systems Node is producing a re- formatted, parallel data set for all of the Saturn encounter data

2. Software

The SOFTWARE directory on each volume contains subdirectories providing both binary (Solaris and Linux) and source code for the data analysis tool, Vanilla, as well as a substantial amount of Vanilla related documentation and examples.

3. Where to go next

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