CALPRODUCT-VS-003: VIS Bias¶
Parent requirement¶
Scheduling¶
One master bias created early on in PV phase.
During routine operations, bias frames are taken during the ROS, and a master bias can be computed whenever a sufficient number of exposures has been obtained.
Time-critical¶
Must be done early during PV phase.
Objective¶
The bias level of the VIS detectors may not be stable over time, and it also exhibits spatial variations at the beginning of the readout (bias stabilization). The spatial pattern is expected to be stable within each quadrant. The bias level can be accurately computed from a series of individual bias exposures.
Fulfilled by¶
Instrument configuration¶
Instrument: VS-CU off; RSU closed; VIS Bias sequence VI-FCP-504 (EUCL-MSS-MA-6-013, v1.3)
Data volume¶
60*276 MB = 16560 MB = 132 Gb (PV phase)
60*276 MB = 16560 MB = 132 Gb (monthly master bias)
Processing input¶
Ground Processing Input Data: BPM
Data Description: 60 VIS biases (for the initial master bias during PV phase), 60 VIS biases per month during routine phase from the ROS observations.
Processing method¶
The master bias is computed from 60 individual exposures. Images are averaged after identification and masking of cosmics.
Processing output¶
Combined bias frames. Monitoring of mean bias level and readout noise (rms) per detector quadrant. Possibly, compute a “master standard deviation map”, i.e. the sigma for each pixel.
Required accuracy, constraints¶
Expected levels within TBD%, stable within TBD%, spatial uniformity within TBD%
Processing tools¶
OU-VIS Bias Processing Element
Validation¶
Single bias exposures:
Within a single quadrant the bias must be stable within 1 ADU (after row averaging, to beat down the readout noise). Within a 24 h period, the bias must not vary by more than 2 ADUs (after row averaging in a difference image). The bias stabilization is not parameterized and not checked in single exposures.
Monthly master bias:
Compute the difference image between the current master bias and previous master bias (taken the previous month, and during PV phase). Sudden changes by more than 1 ADU (TBD) in the mean bias level (quadrant) require further investigation.
Recovery¶
Slow bias variations over timescales of a few months are tolerable for science. The root cause should be investigated. For example, single bias exposures might be affected by too many cosmics and should be rejected. In case of a hardware cause, further investigation by the instrument operation team is required.
Quality control parameters¶
DataModel: https://gitlab.euclid-sgs.uk/
Contact person¶
VIS instrument scientist