.. index:: Bias (VIS) .. _calobs-block-pv-vis-bias: **CALBLOCK-PV-020:** VIS Bias **(DEACTIVATED)** =============================================== .. include:: definitions.rst Observation configuration file ------------------------------ Not applicable (deactivated) Scheduling ---------- One master bias created early on in PV phase (if not taken during commissioning). In case of failure, repeat the master bias at the next possible opportunity. During routine operations, two bias frames are taken every day (included in the ROS). A master bias is computed once a month. Time-critical ------------- Must be done early during PV phase. Dependencies ------------ None. 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. Observations ------------ Early in PV phase, take 60 bias frames. Additional biases are taken as part of the ROS, which is not considered here. Fulfilling ---------- :ref:`calobs-vis-bias` Instrument configuration ------------------------ Instrument: VS-CU off; RSU closed; VIS Bias sequence in the IOCD Methodology / Uplink procedure ------------------------------ :command:`Entity`: VIS :command:`Commanding Method`: VIS: :command:`Dither Sequence`: None Inter-operability constraints ----------------------------- None. Processing input ---------------- :command:`Ground Processing Input Data`: BPM :command:`Data Description`: 60 VIS biases Processing method ----------------- The master bias is computed from 60 individual exposures. Images are median combined (or averaged) after identification and masking of cosmics. Processing output ----------------- Combined bias frames. Processing tools ---------------- Pipeline: VIS_MasterBias_Pipeline PE: VIS_BiasCalibration 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 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: ``_ Contact person -------------- VIS instrument scientist .. raw:: latex \clearpage