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

224 CHAPTER 19. ADVANCED SLICING
19.6.5.1 Wheels position and Detector related variables
The meanings of these variables are straightforward. The detector offset variable is no longer
useful, because there is only one offset per gain of the detector. The important point is the
difference between channel and selection wheel position.
19.6.5.2 Channel versus selection wheel
One of the common mistakes is to think that choosing one of these two variables is enough to
determine if the images are LW ones or SW ones. Think twice: it can happen (due to wheel
motion or dark measurement for examples) that the light beam goes through the SW channel
while the LW detector is on. . . You will then get LW images, but the slicer (and you) will believe
that they are SW ones. It may result that the SCD will not be created if you mix the two kinds
of images.
19.6.5.3 Electronic setup
These two variables are rather important:
• On Board Processing: This variable describes the kind of treatment that is applied to your
observations by ISOCAM’s processor. It can take three values: ‘Normal’, ‘Accumulated’,
or ‘Sampled’. If you work in ‘Accumulated’ mode (frames coadded), CIA will take into
account this kind of observation. Remember two things: in your SCD, the field ‘TINT’
displays the effective integration time, i.e. the number of accumulated frames times the
integration time of the camera for each frame. On the other hand, the field CAL.TINT
gives you the integration time for one individual frame (in CAMTU).
• Observation Mode: This variable tells you if you are observing (‘OBS’), idle (‘IDLE’),
waiting for a good configuration (‘WAIT’), or in GAP or DARK mode. If you are looking
at CUS data (see the value of the Observation Type variable) it is very likely that you will
get an ‘IDLE’ value instead of an ‘OBS’ for your observations. This can be corrected in
the SCDs:
CIA> scd1 = sscd_elem( sscd )
CIA> for i=0, n_elements( scd1 ) - 1 do scd_put, ‘MODE’, ‘OBS’, scd1[i]
19.6.5.4 Observation-related variables
These variables are again simple to understand. Only two remarks have to be made:
• the F RAST variable in telemetry can only be on (1) or off (0). But in an SCD its value
can be ‘RASTER’, ‘MICRO SCAN’, ‘STARING’, ‘TRACKING’ or ‘UNDEFINED’ (see
Section 15.2.1). The definition of a micro-scan is very loose:
M step-size and N step-size ≤ 16 ′′
M step-size or N step-size ≤ 8 ′′
This means that a micro-scan refers to more than the special case of where the step-size
is not an integer number of pixels.