CALBLOCK-PV-024: VIS On-sky Nonlinearity

Observation configuration file

ocf_CALBLOCK-PV-024_NL-NOMINAL.csv

Scheduling

Once, early during PV phase.

In case of failure, repeat as soon as possible.

Time-critical

No.

Objective

Radiation damage may slightly alter voltages in the VIS electronics, changing the VIS nonlinearity as well as the PSF model. The VIS nonlinearity must be monitored continuously in flight.

This CalBlock obtains the nonlinearity estimate from on-sky observations (stellar flux measurements), complementing CALBLOCK-PV-033: VIS Flat Nonlinearity.

Observations

Parallel schedule: CALBLOCK-PV-010: NISP LED flats; This CalBlock is driven by VIS.

Nonlinearity is determined per pixel, folding in a PSF model to account for AOCS jitter. At least 1000 pixels are required per detector quadrant. For a field with stellar density of 2 arcmin-2 in the range V=17.5-21 AB mag (such as at the Self-Cal field), and assuming that one star provides 5 usable pixels, 16 dithers yield about 1760 pixel per quadrant.

Since the data are read out with the shutter open, trailing will occur, which must be fixed at software level. An exposure with 0 seconds integration time will provide information on the trails.

The VIS 4-exposure NL sequence is executed on a stellar field, followed by a dither offset. This will take 4 exposures with exposure times of 0 (flush and readout trails only), 25, 155 and 540s integration time. Repeat 32 times, where every 8 NL sequence begins with a single BIAS acquisition.

Observation instructions 37: VIS on-sky nonlinearity sequence
Slew to VIS NL field

VIS:
Repeat 4x:
   take BIAS
   Repeat 8x:
      Execute predefined VIS 4-exposure NL sequence
      Random dither offset in a 3' box
      Buffer for CDPU processing if necessary

Fulfilling

CALPRODUCT-VS-016: VIS Nonlinearity

Targets and pointing constraints

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

Table 61: VIS nonlinearity field: The area within the Self-cal field without brighter stars is suitable. CSV file

# ID

R.A.

Dec

SELFCAL-FAINT

268.51

65.09

Instrument configuration

Instrument: VIS 4-exposure NL sequence (VI-FCP-501)

Inter-operability constraints

NISP mechanisms must not move while VIS observes on sky.

In-orbit duration

In-orbit Duration: 15.1 h + dither (x32)

Duration of a single 4-exposure NL sequence (repeated 32x):

10s (RD+O+F) + 2*297s (1st-2rd exposures processing) + 545s (4th) + 4*72s (Readout) + 286s (4th processing) = 1723s

Adding a single BIAS before the NL will add another 284 seconds; there will be 4 BIASes in total.

0.6 hours for 32 dither slews.

Note that 66s of the CDPU processing time can be accommodated into the dither/slew duration.

Data volume

4*VB = 1000 MB (BIAS)

32*4*VS = 57856 MB (NL)

If the trailed images compress less efficiently, then the data volume would be higher.

Processing input

Ground Processing Input Data: TBD

Data Description: 128 VIS images

Processing tools

TBD

Quality control parameters

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

Contact person

Calibration lead