The HEASARC Calibration Database

The HEASARC's calibration database (CALDB) system stores and indexes datasets associated with the calibration of high energy astronomical instrumentation. The system can be accessed by users and software alike to determine which calibration datasets are available, and which should be used for data reduction and analysis.

The CALDB was designed to meet the following goals:

  • To allow data reduction and analysis software to be independent of calibration information. This means that calibration information does not need to be hardcoded into software packages. Thus the same calibration datasets can be used by different applications and that software updates are decoupled from calibration updates
  • To allow access to the latest calibration datasets as well as earlier, out-of-date datasets. Thus the CALDB can be used as an archive of past calibrations, and to determine the impact of new calibation datasets on analysis results.
  • To be flexible & system-independent. Flexibility is essential so that the CALDB can be used in a variety of computer system environments, so that new missions/instruments to be added easily and so that the CALDB can be installed and used at any site.

Basic CALDB Design

The above goals are met through use of a simple directory structure for storing files, simple, documented file formats for storing calibration information, and simple "Calibration Index Files" which serve as databases to describe the files and their location on disk.

Because of its wide use in astronomy, all CALDB files are stored as FITS formatted files. This provides great flexibility and computer system independence. Calibration information may be located as an image in the primary data unit, or in one or more image or FITS table extensions.

Calibration files which are part of the CALDB should possess a special set of CALDB header keywords, in addition to the standard FITS keywords and any instrument/project specific keywords. These keywords are used by the CALDB software to create the "CALDB Index File" databases.

For quick reference:

  • A table listing the CALDB Header Keywords, with brief definitions, is available
  • As an example see this ASCII dump of the headers for one of the ROSAT Position Sensitive Proportional Counter Detector Maps Currently archived in the CALDB.
  • Also take a look at this dump of the Calibration Index File for the ROSAT Position Sensitive Proportional Counter.
  • Perl scripts to install a CALDB, manage a HEASARC-style CALDB, and manage a local CALDB augmented with non-standard calibration files are available.