CALBLOCK-PV-017: NISP Reciprocity Failure

Observation configuration file

ocf_CALBLOCK-PV-017_PHOTO-H.csv
ocf_CALBLOCK-PV-017_PHOTO-J.csv
ocf_CALBLOCK-PV-017_PHOTO-Y.csv

Scheduling

Once, during PV phase

In case of failure, repeat at next possible opportunity.

Objective

Validate the reciprocity failure (flux-dependent nonlinearity, charge trapping) for each detector. Trapping and detrapping effects are poorly understood, impact photometric measurements, and exhibit strong spatial variations across detectors. This validation is a spot check to see whether anything has changed since the more extensive ground characterization, and to obtain similar measurements with real targets under in-flight conditions.

Trapping/detrapping is likely wavelength independent. However, in-flight and with all instrumental effects “turned on”, we must verify this assumption. Hence the procedure outlined below will be repeated for all three filters.

Observations

To test the functional behaviour of reciprocity failure or trap filling on photometry, the same sources are observed with and without additional background light. The expectation is that additional background signal passivates the traps more quickly, and hence more source photons are detectable.

Execute 8 dithered photo-MACC at the Self-cal field, without LED light. Take 4 more dithered photo-MACC and with additional LED background flux. Repeat this 18x with increasing LED fluxes of 2, 4, 8, … , 512 e-/s/pixel, providing additional background signal between 170-44000 e-/pixel in a 87s integration-time MACC(4,16,4) image. Ideally, higher resolution at lower LED fluxes is desirable, but the LEDs have not been characterized at extremely low fluxes. LEDs A to C cannot all be commanded to realise the lowest 2 e-/s/pixel and 4 e-/s/pixel flux settings.

Typical total background levels (zodi, in-field and out-field straylight) in a photo-MACC exposure are on the order of about 160 e-/pixel in J-band (15-20% lower in Y and H).

The procedure is executed 3 times, for Y-band and LED B, J-band and LED C, and H-band with LED D.

The stars will fall into different pixels and detectors in the exposures without and with LED illumination. It is sufficient to infer the general behaviour, using a sufficiently large number of stars.

Observation instructions 28: Observing instructions for NISP reciprocity failure
for filter in [Y,J,H]:
    if filter == "Y":         LED = "B"
    if filter == "J":         LED = "C"
    if filter == "H":         LED = "D"

    for LED flux_i in [2, 4, 8, ... , 512] e-/s:

        if low LED fluxes not commandable: continue

        Repeat 8x: (persistence decay, measurement without LED)
            "1 NISP photo-MACC exposure"
            "Random dither offset in a 3' box"

        Repeat 4x:
            "Turn on LED with flux_i"
            "1 NISP photo-MACC exposure"
            "Turn off LED"
            "Random dither offset in a 3' box"
Table 54: NISP LED flux lookup table. Numbers in parentheses were not verified on ground, but are reasonably close to be extrapolated. Missing data values indicate negative PWM values when using linear extrapolation. CSV file

# Flux [e-/s]

Flux [ADU/frame]

Int-A [mA]

PWM-A [%]

Int-B [mA]

PWM-B [%]

Int-C [mA]

PWM-C [%]

Int-D [mA]

PWM-D [%]

Int-E [mA]

PWM-E [%]

#

LED A

LED A

LED B

LED B

LED C

LED C

LED D

LED D

LED E

LED E

2

1.45

1.0

21.4

1.0

8.6

4

2.91

1.0

5.0

1.0

26.1

1.0

11.4

8

5.82

1.0

8.2

1.0

11.9

1.0

5.4

1.0

35.4

1.0

17.0

16

11.6

1.0

18.8

1.0

29.2

5.0

6.3

5.0

7.2

1.0

28.2

32

23.3

1.0

39.8

5.0

17.1

5.0

11.6

5.0

9.9

5.0

8.9

64

46.6

5.0

21.9

5.0

30.6

5.0

22.2

5.0

15.4

5.0

14.4

128

93.2

5.0

41.8

10.0

30.2

5.0

43.3

5.0

26.3

5.0

25.5

256

186.3

10.0

43.9

30.0

19.8

10.0

45.4

5.0

48.2

10.0

21.8

512

372.7

30.0

30.0

30.0

39.4

30.0

30.5

10.0

32.0

30.0

11.6

Fulfilling

CALPRODUCT-NI-013: NISP Reciprocity Failure

Targets and pointing constraints

Pointing: Straylight suppression as per MOCDA-SYS-003.

Table 55: Self-cal center. CSV file

# ID

R.A.

Dec

SELFCAL-CENTER

268.812745

65.2855857

Instrument configuration

Instrument: NI-CU on, NI-GWA open, VS-CU off

Inter-operability constraints

None

In-orbit duration

In-orbit Duration: 16.9 h

Assuming 70 s for each dither offset, plus 20 s (estimate) for NI-CU turn-on/off. 9 sequences with and without LED, 4 dithers, 3 filters.

((111+70)s*12 + 4*20s) * 9 * 3 = 16.0 h

Data volume

324*NP = 19116 MB

Processing input

Ground Processing Input Data: All calibration products to run the standard science pipeline (BPM, darks, flat, nonlinearity etc), reference measurement of standard star, RSR curves (relative spectral response of the system (mirrors, optics, instrument)

Data Description: 324 photo-MACC images

Processing output

Measure the flux of unsaturated stars without and with additional background light. Determine the percentage or decade of flux reciprocity failure, if present. Comparison with a model prediction from ground characterization data if available.

Required accuracy, constraints

TBD

Processing tools

L1 science pipeline and absolute calibration pipeline, additional offline trend analysis of flux measurements

Quality control parameters

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

Contact person

NISP-P calibration scientist