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

256 CHAPTER 20. ADVANCED DATA CALIBRATION
is involved. Depending on the type of calibration data, certain parameters are given precedence
and others are completely ignored.
Usually all this is handled automatically by CIA. When get sscdraster, get sscdstruct
and get sscdcvf build a PDS from an SSCD, they choose the optimal calibration record from
the CDS for your observation data. These records are placed in the substructure .CALG (Section
15.5.6).
However, if you have your own CDS and an SPD SCD, then likewise you can use find best
or find best psf to extract the most suitable record for you data.
20.12.1 find best
find best is used for all calibration data types except PSF data (see Section 20.12.2).
Suppose that we have a an SCD and an OFLT CDS in memory:
CIA> spd_scd = ’CSCDLW3FOV6V4P00_96052803472412’
CIA> oflat_cds = ’CCGLWOFLT_96030223551347’
CIA> best_oflat = find_best( spd_scd, oflat_cds )
best oflat is a full record from the CDS.
CIA> help, oflat_cds, /str
CIA> OFLT = oflat_cds.image[*,*,0]
Note that find best finds the flat-field with the closest wavelength to that of the observation
data (not with the closest wheel index).
20.12.2 find best psf
This routine is used in a similar way to find best but of course it is just for PSF calibration
data. See the on-line help or cia help for more details.
20.13 Unit conversion and colour correction
This section describes how pixel units are handled in CIA and how users may convert their
images into milli-janskys (mJy).
20.13.1 Propagation of pixel units within a PDS
The IMAGE pixels values in a freshly made, uncalibrated PDS, will be in units of ADUs.
CIA> print, pds.cube_unit
ADU
After dark correction the same pixels will be in units of ADU/gain/second.