.. index:: PRNU (VIS), Brighter-fatter effect(VIS) .. _calobs-block-rec-vis-flats: **CALBLOCK-REC-001:** VIS flat fields ===================================== .. include:: definitions.rst Observation configuration file ------------------------------ | :download:`ocf_REC-001.csv ` Scheduling ---------- Once, after full thermal decontamination. In case of failure, repeat at next possible opportunity. Time-critical ------------- No Dependencies ------------ VI-CU commissioned Objective --------- .. index:: PRNU (VIS) Obtain near-monochromatic flat fields using some of the 6 LEDs in VI-CU. They are the basis to recalibrate :ref:`calobs-vis-prnu` and :ref:`calobs-vis-ptc`. Observations ------------ * **PRNU and BFE:** Obtain pairwise flats with dithers between pairs, at fluences 40 kADU (5 pairs), for each of LED1 to LED4. Like this, a S/N of about 1000 per pixel per fluence is achieved, assuming a gain of 3.48 e-/ADU, and allowing for 10% variation in gain and flatfield illumination. The total S/N should be up to 1700 before masking cosmic rays and bright sources. * **PTC (=Gain):** Obtain pairwise flat fields with dithers in between, with fluence 1 kADU (10x pairs) for LED3 only Direct (Short Science [SS]) observations of a stellar field (SelfCal) are also required, because pixel correlation in flat fields can appear enhanced around coherent sources. The spacecraft must not dither or slew during VIS flat field exposures. A science exposure is required for each dither to enable object masking, and sky-background correction. .. code-block:: none :caption: **Flat-field pairs for PRNU and PTC calibration** The integration time of the short science (SS) exposure is defined by the ROS (95 s total, including 5.48 s for the shutter movements). Dithers are random in a 3' box. BIAS Repeat 5 times: 2 flats LED_3 with fluence 1 kADU 2 flats LED_3 with fluence 1 kADU SS, dither BIAS Repeat 5 times: 2 flats LED_1 with fluence 40 kADU 2 flats LED_2 with fluence 40 kADU SS, dither 2 flats LED_3 with fluence 40 kADU 2 flats LED_4 with fluence 40 kADU SS, dither Fulfilling ---------- :ref:`calobs-vis-prnu` :ref:`calobs-vis-ptc` Targets and pointing constraints -------------------------------- :command:`Pointing`: Straylight suppression as per MOCDA-SYS-003. The target should allow an SAA/AA as for the later PDC observations in the recalibration plan. Instrument configuration ------------------------ Instrument: VI-CU on Methodology / Uplink procedure ------------------------------ :command:`Entity`: VIS :command:`Commanding Method`: VIS: :command:`Dither Sequence`: Random dither offsets in a 3' box Inter-operability constraints ----------------------------- None. In-orbit duration ----------------- :command:`In-orbit Duration`: 8.5 h + 15x dithers (>0.3h) Note that 66s of the CDPU processing time can be accommodated into the dither/slew duration. 1k ADU, 1 LED: 2.5 h + dither (x5) (CDPU processing buffer time for 1k ADU Flats: 295s) 40k ADU, 4 LEDs: 5.9 h + dither (x10) (CDPU processing buffer time for 40k ADU Flats: 380s) 5+10 = 15 dither slews: 15*66s = 0.3 h Data volume ----------- Update as needed ``Total = 52,680 MB`` ``15*VS + 2*VB = (6,780 + 500) = 7,280 MB`` ``20*VF = 11,400 MB`` (``VF=570 MB``) ``40*VF = 34,000 MB`` (``VF=850 MB``) Processing input ---------------- :command:`Ground Processing Input Data`: BPM, nonlinearity calibration correction, ground-based QE :command:`Data Description`: Total: 60 flats, 15 SS, 2 biases Processing output ----------------- Normalized combined flat fields for each LED used Required accuracy, constraints ------------------------------ Expected flux levels within TBD%, stable within TBD%, spatial irradiance as expected (within requirement, ground-based measurements) Processing tools ---------------- Pipeline: VIS_MasterFlat_Pipeline PEs: VIS_BiasCorrection, VIS_PRNUCalibration Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- VIS instrument scientist .. raw:: latex \clearpage