CALPRODUCT-VS-009: VIS Darks¶
Parent requirement¶
Scheduling¶
Once, during PV phase.
During routine operations, 4 darks are taken per day as part of the ROS, with the following integration times: 2x 325s, 1x 200s, 1x 95s.
Time-critical¶
No.
Objective¶
The dark current of the VIS detectors is expected to be extremely low, \(\leq 0.01\,{\rm e}^{-}\,{\rm s}^{-1}\,{\rm pix}^{-1}\). It could not be fully characterized (overall amplitude, temperature dependence) on ground, though minimal characterization during the CSL TVac tests have shown the dark current at nominal operational temperature to be extremely low (0.1 ADU upper limit / 350s integration time, EUCL-MSS-TR-6-135 v1.0 §5.7). We assume that all variations in the dark current, both spatially and temporally, will introduce an error into the relative photometric error that is lower than the budget allocation.
With these observations we determine the true VIS dark current at operational temperatures. The exposures are also used to check the cosmic ray flux, the cosmic ray removal routine, to update the pixel cosmetic map, and to provide an initial estimate of the CTI.
Observations¶
PV phase: See CALBLOCK-PV-021: VIS Bias and Dark
Routine phase: 4 darks are taken per day by means of the ROS
Fulfilled by¶
In-orbit duration¶
Data volume¶
60*325 MB = 19500 MB = 156 Gb (PV phase)
120*325 MB = 39000 MB = 312 Gb (monthly darks from the ROS)
Processing input¶
Ground Processing Input Data: BPM
Data Description: 30 VIS images each for the nominal and short darks in PV phase. 60 darks of 325 s, 30 darks of 95 s, 30 darks of 200s per month in the nominal phase. A master BIAS is required in both cases and computed from interleaved bias exposures.
Processing method¶
The master darks are computed from a set of 30 individual exposures. Images are median combined (or averaged) after identification and masking of cosmics. A higher S/N master dark for the nominal science integration time can be computed when more such darks become available.
Processing output¶
Combined nominal and short dark frames. Estimated dark current, updated cosmetics map.
Required accuracy, constraints¶
Expected levels within TBD%, stable within TBD%, spatial uniformity within TBD%
Processing tools¶
OU-VIS DARK Processing Element
Validation¶
Single dark exposures:
Number of cosmics below some TBD threshold.
Monthly master dark:
Number of warm and hot pixels below some TBD threshold.
Quality control parameters¶
DataModel: https://gitlab.euclid-sgs.uk/
Contact person¶
VIS instrument scientist