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

214 CHAPTER 19. ADVANCED SLICING
19.3 A beam-switch observation caveat
Some observers have programmed their beam-switch observations in reverse – this means that
the reference field is programmed as the source field and vice versâ. This problem will become
apparent when the final beam-switch MOSAIC image is viewed (as contained in the BS PDS
field .RASTER). The MOSAIC will appear inverted and will incorrectly have the astrometry of
the reference field. To counter this problem set the keyword /reverse when calling get sscdbs
to re-reverse the fields in the created BS PDS:
CIA> bs_pds = get_sscdbs( bs_sscd, /reverse )
19.4 Advanced slicing of beam-switch data (CAM03)
This section introduces the CIA user to advanced concepts in slicing beam-switch data.
19.4.1 Concatenating intermediate SCDs in a beam-switch observation
The slicing keyword bs may be of interest to observers with beam-switch data. Beam-switch
observations have an intermediate step which occurs while slewing and data accrued in this
step will appear in an SCD. Normally this SCD is considered to contain invalid data, though
in reality this data may be quite usable. Setting /bs will make spdtoscd merge this SCD with
the previous SCD and users can later manually unmask this ‘invalid’ data for inclusion in the
finally MOSAIC image. In addition using the keyword /bs has the added advantage of making
it possible to use sscd clean on the SCDs.
Compare the following with Chapter 6.
CIA> spdtoscd, ’cisp05804610.fits’, sscd, dir=’$cia_vers/test’, /nowrite
CIA> sscd_info, sscd
15 SCDs in the SSCD: CSSC058046100101_98092617482201
seq channel mode fltrwhl pfov tint gain offset size ra dec
0 LW IDLE LW2 6.0 25.20 1 512 1 ******* *******
1 LW IDLE LW2 6.0 2.10 2 512 1 ******* *******
2 LW OBS LW2 6.0 2.10 2 512 1 ******* *******
3 LW OBS LW2 6.0 2.10 2 512 1 ******* *******
4 LW OBS LW10 1.5 2.10 2 512 14 295.462 50.518
5 LW OBS LW10 1.5 2.10 2 512 47 295.462 50.518
6 LW OBS LW10 1.5 2.10 2 512 48 295.437 50.547
7 LW OBS LW10 1.5 2.10 2 512 48 295.462 50.517
8 LW OBS LW10 1.5 2.10 2 512 47 295.417 50.501
9 LW OBS LW10 1.5 2.10 2 512 48 295.463 50.518
10 LW OBS LW10 1.5 2.10 2 512 47 295.488 50.488
11 LW OBS LW10 1.5 2.10 2 512 48 295.463 50.518
12 LW OBS LW10 1.5 2.10 2 512 28 295.508 50.534
13 LW IDLE LW10 1.5 2.10 2 512 24 295.463 50.518
14 LW IDLE LW2 6.0 25.20 1 512 1 ******* *******
CIA> cleaned_sscd =
Out of 15 SCDs:
sscd_clean(sscd)