Euclid CalF

The CalF defines in-flight calibration products and survey characterizations, as set out in the CalCD-B. The PV plan and the routine calibration plan derive from the CalF. The following assumptions and principles are used:

CalProduct: In-flight calibration products

Some CalProducts are directly observable (e.g. darks), others are derivative (e.g. zeropoints). All CalProducts have a correspondence in a CalBlock that provides the relevant data.

Resulting pixel data and dynamic parameters are stored in the Euclid Science Archive System (SAS). Static parameters are stored in the Mission data base.

Characterization: Survey and system characterizations

A Characterization is a data product or measurement derived from observations, characterizing either the target sample, the sky, or the telescope. These measurements enter either at the survey planning stage, or at the L3 processing level. All Characterizations have a correspondence in a CalBlock that provides the relevant data.

CalBlock: In-flight calibration observation blocks

Most CalBlocks provide data for one or more CalProducts, with a few exceptions such as survey characterizations, zodi model validation, and first light observations.

Routine Phase Observations

These blocks are executed during routine phase, only. Similar blocks exist for PV phase, where e.g. higher S/N or spatial sampling is needed.

PV Phase Observations

These blocks must be executed during PV phase. Some of them are repeated in identical or modified form in the routine calibration plan. All PV CalBlocks can be repeated during the routine phase if necessary.

Total planned PV time: 1219.7 h or 50.8 days (without phase diversity, and neglecting parallel execution)

Minimally-invasive decontamination recovery

Selected optical elements are heated to a peak temperature of 160 K for about 1h. The NISP and VIS instruments remain operational during this time. The VIS shutter is closed to protect the detectors, and the FGS continues guiding. No offsets are permitted so that a continuous FGS light curve can be obtained through the thermal cycle.

Observations and recalibration: After a minimum time of 20 minutes at 160 K, take a ROS_D1 with random dithers in a 3’ wide box, or a continuous repetition of CALBLOCK-F-014: Contamination scan like scans until the mirror temperatures are within 0.1 K of their initial temperatures, or have stabilised to within 0.1 K.The thermal cycle must be bracketed by CALBLOCK-F-001: Self Calibration, to judge the improvement of throughput and to provide a new reference point for subsequent survey observations. The bracketing should be as close in time as scheduling allows.

Full thermal decontamination recovery

Within the series of recalibrations, a single defocused CALBLOCK-F-013: Phase Diversity observation is needed at the VIS-PDC-NEP field. During the preceding calibrations the spacecraft shall maintain the SAA and AA angle that will be realised later-on at that VIS-PDC-NEP field. Calibrations that affect the baseplate temperatures more than normal ROS-like observations must come after CALBLOCK-F-013: Phase Diversity.

Immediately before full decontamination: Off-sky calibration.

  1. CALBLOCK-REC-003: VIS CTI Charge Injection and Trap Pumping A minimal set of CIL/VTP/STP to confirm any changes in the VIS detector trap density and charge-injection levels. CTI calibration must be bracketed with the full decontamination segregating the pre- and post-decontamination CTI calibration regions, as heating is expected to change the trap density.

Full Decontamination. Both VIS and NISP instruments are powered down during spacecraft warm-up.

During telescope cool-down: Off-sky calibrations. The instruments must be at their at operational temperatures, representative for the survey operations that follow:

  1. CALBLOCK-PV-014: NISP Baseline Map

  2. CALBLOCK-PV-016: NISP Persistence (nominal persistence calibration, only; skip checks 1 and 2)

  3. CALBLOCK-PV-018: NISP Nonlinearity (full)

  4. CALBLOCK-PV-021: VIS Bias and Dark (may be skipped if running out of allocated time)

  5. CALBLOCK-REC-001: VIS flat fields

After cool-down: Optical alignment, focusing, then on-sky calibrations:

  1. CALBLOCK-F-001: Self Calibration

  2. CALBLOCK-REC-003: VIS CTI Charge Injection and Trap Pumping See comment on item (0) above. The Serial Trap Pumping (STP) variant of this CALBLOCK must immediately precede CALBLOCK-PV-008: Phase Diversity Calibration, to allow the BIAS level to settle during the PDC observations.

  3. CALBLOCK-PV-008: Phase Diversity Calibration (only one full SAA/AA setting at the VIS-PDC-NEP field, once thermal stabilisation has concluded)

  4. CALBLOCK-REC-002: VIS Flat Nonlinearity (high temperature stability in VI-CU and VI-FPA required)

  5. CALBLOCK-F-011: NISP Reciprocity Failure

  6. CALBLOCK-REC-004: NISP LED flats (Clone of F-007 with the VIS-portion removed)

  7. CALBLOCK-PV-004: Internal straylight check (NDI check, only)

Additional checks to be run with the data obtained: