CALBLOCK-REC-001: VIS flat fields

Observation configuration file

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

Obtain near-monochromatic flat fields using some of the 6 LEDs in VI-CU. They are the basis to recalibrate CALPRODUCT-VS-014: VIS LED Pixel Response Non-uniformity (PRNU) and CALPRODUCT-VS-011: VIS Photon Transfer Curve (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.

Observation instructions 56: 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

CALPRODUCT-VS-014: VIS LED Pixel Response Non-uniformity (PRNU)

CALPRODUCT-VS-011: VIS Photon Transfer Curve (PTC)

Targets and pointing constraints

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

Inter-operability constraints

None.

In-orbit duration

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

Ground Processing Input Data: BPM, nonlinearity calibration correction, ground-based QE

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: https://gitlab.euclid-sgs.uk/

Contact person

VIS instrument scientist