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There are currently four observing modes with WHIRCAM. These are:
- STARE - the array is reset, read after the user-defined
on-chip exposure times, and reset again.
- ND_STARE - the array is reset and read immediately and read again
after the user-defined on-chip exposure time. The difference between
the post-exposure and pre-exposure images is taken and stored.
- S+A - In Shift-and-Add mode, images are pre-processed in ALICE.
The peak pixel in a user-definable area is found and the image is
shifted (by integer pixels) so the peak pixel falls onto a fiducial mark on
the array. N images are co-added in this manner. S+A mode works in STARE
mode only and is used to sharpen images and reduce seeing/tracking effects.
The user is referred to § 8 for more details.
- Atmospheric Monitoring imaging - intended to allow monitoring of
such things as seeing and image stability, but not yet implemented.
The two advantages of ND_STARE over STARE is that (1) the direct read-out
architecture of the detector means that the integrated
charge may be sampled non-destructively and an improvement in read-noise
is thus obtained by making multiple reads, and (2) the reset level can vary,
so you automatically subtract the latest reset in ND_STARE. However, there is
also an extra time overhead in each readout, so for very short exposures
(as in S+A) STARE is better. The shortest integration where
ND_STARE is likely to be beneficial is about 1 sec.
Thu Mar 14 14:48:38 GMT 1996