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

38 CHAPTER 5. SOLAR SYSTEM OBJECT OBSERVATION (CAM01)
7. The final step in the data reduction is to create the MOSAIC image. This is really
just the average of all the IMAGEs in sso pds.cube and we can easily derive it with CIA’s
reduce cube. Before doing so we must do a ‘fake’ reduce as we normally do when reducing
a raster PDS, BS PDS or CVF PDS. This is really just to keep the PDS consistent with
the data reduction step by making sure important fields, such as sso pds.image unit, are
updated.
CIA> reduce, sso_pds
Now you can take a look at the EXPOSURE obtained for each SCD or pointing of the
spacecraft. These images should look very much alike – all will be slightly smeared. This
smearing is due to steps ISO makes as it re-points, i.e. the tracking is of course not
smooth. You will also notice that the position of the object may be slightly different
from EXPOSURE to EXPOSURE. This second effect is due to the inaccuracies of ISO’s
pointing.
CIA> x3d, sso_pds
Now we will do the ‘real’ reduce manually. The MOSAIC image is stored in the first frame
of sso pds.image:
CIA> sso_pds.image[*,*,0] = reduce_cube(sso_pds.cube, mask=sso_pds.mask)
Flat correction finishes off this reduction step:
CIA> corr_flat, sso_pds
8. So to view the results of your calibration use xdisp or tviso, specifying the first frame of
sso pds.image as input:
CIA> tviso, sso_pds.image[*,*,0]
You should see the same image as in Figure 5.1. The effects that we saw earlier in Step
7withx3d (smearing and pointing inaccuracies) will have combined to make the comet
look somewhat blurred in this final MOSAIC image.
9. Now we can convert the MOSAIC image from ISOCAM units into milli-janskys (mJy):
CIA> conv_flux, sso_pds
10. As in the end of Section 3.2 you can save the data using IDL’s SAVE:
CIA> save, file=’sso_pds.xdr’, sso_pds
Export to FITS may be performed with CIA’s imagette2fits. This routine will place the
data in the field sso pds.image, and hence the MOSAIC image, into the primary array of
the FITS file:
CIA> imagette2fits, sso_pds, name="tempel-tuttle.fits", rank=0
We use the keyword rank to specify the MOSAIC image, i.e. the first frame of sso pds.image.
This image is written to the file tempel-tuttle1.fits.
An improved method to analyse solar-system observations can be found in section 20.7