CALPRODUCT-NI-005: NISP Cross-talk¶
Parent requirement¶
Scheduling¶
Once. During PV phase, we determine at which magnitude we start seeing cross-talk effects, to build a first masking model.
Time-critical¶
No.
Objective¶
Cross-talk is caused within the SCA (sensor chip array, or ‘detector’) as well as the SCE (sensor chip electronics). The crosstalk amplitude is on the order of 0.001%, and therefore detectable only for super-saturated field stars. The single pixel reset (SPR) method can be used only for fluences up to saturation, and hence is not usable here.
We determine the magnitude limit at which very bright field stars cause intra-chip (or channel-to-channel) cross-talk between each of the 32 readout channels of a detector, as well as cross-talk between detectors (inter-chip cross-talk). Like CALPRODUCT-NI-012: NISP Persistence, the corresponding pixels must be masked if violating the CalCD-B requirements.
The analysis is based on normal science observations from the survey. As deeply saturating stars (AB<12) have a density of \(0.02\;{\rm arcmin^{-2}}\) at the northern galactic pole (i.e. about 2 per detector), the analysis should become feasible after a few hundred fields have been observed.
Fulfilled by¶
Targets and pointing constraints¶
Normal wide survey fields can be used to determine the crosstalk for deeply saturating stars
Instrument configuration¶
Instrument: NI-CU off, NI-GWA open, NI-FWA Y+J+H, VS-CU off
Inter-operability constraints¶
None.
Processing input¶
Ground Processing Input Data:
Data Description:
Processing method¶
Given the known locations of the offending sources (stars), look for ghosts at corresponding positions in the other readout channels and detectors. Depending on the amplitude of the cross-talk signal, several exposures might be required to measure and detect the crosstalk flux using aperture photometry in the known locations of the crosstalk images.
Processing output¶
Updated cross-talk matrices for intra- and inter-chip cross-talk.
At a first step, determine the faintest AB magnitude of saturated stars whose crosstalk signal would start violating R-CAL-B-NP-1480 (NISP-P) and R-CAL-B-NP-2480 (NISP-S), within the same detector, and between detectors.
We do not only need the amplitudes, but also the location of the victim pixels as a function of location of the offending source. Depending on clocking, readout, and detector orientation, this might not be at the expected locations. The easiest way to determine the mapping would be from extremely bright stars that cause an obvious crosstalk signal.
At a second step, a more fine-tuned model could be built if we see e.g. considerable significances in crosstalk amplitude within a detector. Perhaps only immediately neighboring channels are affected. This will only be known once in flight.
Processing tools¶
TBD.
Validation¶
The crosstalk S/N can be arbitrarily increased by stacking the ghosts of multiple, (un)saturated stars in the same readout channel. The cross-talk amplitude is not expected to depend on the location inside a given readout channel.
Recovery¶
None. The cross-talk thresholds / models are built from survey data.
Quality control parameters¶
DataModel: https://gitlab.euclid-sgs.uk/
Contact person¶
NISP-P calibration scientist