ISOCAM Interactive Analysis User's Manual Version 5.0 - ISO - ESA

15.3. CALIBRATION DATA STRUCTURE (CDS) 171
15.3 Calibration Data Structure (CDS)
One generic structure is used to contain all of the different types of calibration data. This
is the Calibration Data Structure. It contains a dynamic substructure or field named DATA
(see Section 15.3.2) and a standard set of fields (see Section 15.3.1). DATA holds the actual
calibration data: dark images, flat images, point spread images, etc. The standard fields holds
information related to the nature of the CDS structure itself, e.g. the CDS name and size.
The CDS is almost a direct conversion from FITS format data to IDL data structure, the
important difference being that the actual image data is scaled, so the BZERO and BSCALE
keywords are discarded. So the CDS differs from the CIA data structures in that the CAM
parameters are NOT presented in the CIA user friendly format, but as raw values taken from
the CAL-G FITS files.
The CDS is not a structure that you need to be very familiar with. It is mainly handled by
CIA routines. For example, get sscdraster will automatically obtain OFLT, DFLT and DARK
CDSs from the CAL-G archive for calibration of a PDS. However if you wish to view the data
in a CAL-G file, you can use CIA conversion routines to make a CDS and convert the CAM
parameters to a readable format (we give an example later in this section). Alternatively you may
use IDL’s Astronomy Library routines and follow the guidelines in the ISOCAM Handbook. In
any case, a detailed explanation of the CAL-G FITS files can be found in the ISO Data Product
Document. You may also need to refer to the ISO Satellite Handbook and ISOCAM Handbook
for explanation of CAM parameters.
15.3.1 Standard fields of the CDS
The standard fields of the CDS are listed here.
1. NAME: Generally of the form,
CCGCCTTTT yymmddhhmmssdd 7
where,
Variable
Definition
CC Channel, i.e. LW or SW
TTTT CDS name of calibration data (see Table 15.3.2)
yy year of creation
mm month of creation
dd day of creation
hh hour of creation
mm minute of creation
ss second of creation
dd 0.01 second of creation
Note that if the CDS is created from a CAL-G file, i.e. using calg2cds (see Section 17.1.5,
then creation refers to the date of creation of the CAL-G file and NOT the date the CDS
was created. Should the CDS have been created using cds init (see section 16.1.1.5), then
creation refers to the date cds init was executed.
2. SPARE: This is an empty array. Type: byte 1-D IDL array.
7 There are some exceptions to this rule, e.g. the GAIN CDS is named CCIGAIN yymmddhhmmssdd.