The Calibration Database

The calibration database consists of a directory containing all reduced calibration files needed by the GPI DRP, and associated software for indexing and accessing the calibration files. The location of the calibration data directory is configured upon system installation.

As new calibration data are reduced, they are automatically saved into the calibration DB. As other data are reduced, by default the pipeline queries the calibration data to find the most appropriate calibration information for each task. (Users may explicitly select calibration files if desired, using the Recipe Editor tool).

The index of available calibrations is maintained in a FITS bintable file called GPI_Calibs_DB.fits located in the calibrations directory. (For convenience, a human-readable copy of this file is also saved, in plain text format. This can be used to quickly examine by eye its contents) The index table contains a list of various keyword values of the reduced calibration data that can be used by the calibration DB software to assign appropriate calibration

The fields which are tracked are:

1. Directory path (Currently all files are stored in the same calibrations directory, but we save the path explicitly to support potential future upgrades to this directory layout).
2. Filename of the reduced calibration data
3. Data type (e.g. Dark, wavelength calibration, flat field, etc)
4. Prism (to differentiate between spectral and polarimetric mode)
5. Filter
6. Apodizer
7. Lyot
8. Port of the Gemini Instrument Support Structure (side, bottom). This is relevant for instrumental polarization calibration.
9. Exposure time
10. date of acquisition of the raw file (in JD), or the most recent if the calibration is a combined product from several raw files

How the Calibration Database Selects Which File to Return

Below is a list of the Criteria used to select the correct recipe to reduce a given type of calibration file. The values for the Type, Exposure Time, Data, Filter, and Prism are pulled from the image headers of the raw files.

Calibration File	Criteria
Dark	Type, Exposure time, date
Wavelength solution	Type, Filter, Prism, Date
Polarimetry spots cal	Type, Filter, Prism, Date
Master flat	Type, Filter, Prism
Bad pixel map	Type, Date
Plate scale & orientation	Type, Date
Spot locations	Type, Filter, Prism, Date
Grid ratio	Type, Filter, Prism, Date
Distortion	Type, Date
Flux conversion	Type, Filter, Prism, Date
Telluric transmission	Type, Filter, Prism, Date
Instrumental polarization	Type, Filter, Prism, Date

The rules for matching files are detailed here.

Maintaining the Calibration Database

For the most part, the calibration database software takes care of maintaining itself in a fairly automatic manner. As new calibration files are reduced, the DRP software updates in real-time the calibration database.

The calibration file index can be re-created at any time if needed by pressing the ‘Rescan Calib. DB’ button in the pipeline Status Console. For instance, if you want to copy or move calibration files from one computer to another, on the destination computer you should rescan the database and it will pick up any new files that were added.