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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earlier, out-of-date datasets.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.
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