.. index:: Crosstalk (NISP); Electronic (between channels and detectors), Crosstalk (NISP); Calibration observations .. _calobs-block-pv-nisp-crosstalk: **CALBLOCK-PV-013:** NISP Cross-talk **(DEACTIVATED)** ====================================================== **Deactivated:** After an optimization round at Goddard, the NISP crosstalk amplitude is on the order of 0.001%, which even for stars at the saturation limit would be detectable only after stacking a larger number of images. Crosstalk will still be checked for in normal survey images for supersaturated field stars. .. include:: definitions.rst Observation configuration file ------------------------------ Not applicable (deactivated) Scheduling ---------- Once, during PV phase. In case of failure, repeat at next possible opportunity. Time-critical ------------- No. Objective --------- .. index:: Single pixel reset method (SPR); electronic cross-talk The *single pixel reset (SPR)* method is applicable in case of high crosstalk amplitudes. We must measure **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). The cross-talk is potentially fluence dependent. The :ref:`single pixel reset (SPR) method ` can be used up to saturation for both types of cross-talk. Inter-chip cross-talk might be absent or of very low amplitude. If the SPR method does not reveal any inter-chip cross-talk, then we can use deeply saturating stars instead. A dedicated stand-alone procedure would require placing a bright star in 512 different locations (32 channels in 16 detectors), which is too expensive. Instead, we perform this analysis using normal science observations from the survey. As deeply saturating stars (AB<12) have a density of :math:`0.02\;{\rm arcmin^{-2}}` at the northern galactic pole (i.e. about 2 per detector), the analysis becomes feasible after a few hundred fields have been observed. Observations ------------ Using the SPR method, reset the bias level for 16x16 superpixels, in each of the 32 readout channels. Apply 64 pixel offsets between these superpixels (see the figure below), such that all channels of one detector can be probed with a single exposure, and one is still able to unambiguously associate the ghosts with their offending sources. The following "fluences" are tested: 5% full-well: 10 SPR exposures 25% full-well: 5 SPR exposures 50% full-well: 5 SPR exposures 75% full-well: 5 SPR exposures 90% full-well: 5 SPR exposures Repeat for each of the 16 detectors, i.e. a total of 480 exposures. The SPR method supports both intra-chip as well as inter-chip cross-talk models. If the inter-chip cross-talk is very low, saturated sources might reveal it. .. _figure_xtalk_pv: .. figure:: ../images/xtalk_dcl.png :scale: 100 :align: left 16x16 superpixels with reset bias level, offset by 64 pixels each in the horizontal and vertical direction of a Euclid H2RG. Image credit Goddard DCL. Fulfilling ---------- :ref:`calobs-nisp-crosstalk` Targets and pointing constraints -------------------------------- :command:`Pointing`: No angle constraints The SPR method requires no dedicated pointing. Normal wide survey fields can be used to determine the crosstalk for deeply saturating stars. Instrument configuration ------------------------ Instrument: 7: Calibration IPC; NI-FWA closed, NI-GWA RSG000. Single detector readout for the SPR method. Must read out the detector to which the SPR method was applied. Methodology / Uplink procedure ------------------------------ :command:`Entity`: NISP :command:`Commanding Method`: NISP: Observation :command:`Dither Sequence`: None. Inter-operability constraints ----------------------------- VIS-CU off (if increasing NISP background). VIS may execute normal observations on sky. In-orbit duration ----------------- :command:`In-orbit Duration`: 0 h (deactivated) ``(30*16*111) s = 14.8 h`` Data volume ----------- ``480*8 MB = 3840 MB`` (file size of 8 MB for a single detector is an estimate) Processing input ---------------- :command:`Ground Processing Input Data`: :command:`Data Description`: Processing method ----------------- Given the known locations of the offending sources (stars, or injected signal), 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 the ghost flux accurately, e.g. using aperture photometry or direct integration over the known footprint shape (in case of the SPR method). Processing output ----------------- Updated cross-talk matrices for intra- and inter-chip cross-talk. We do not only need the amplitudes, but also the location of the victim pixels as a function of location of the offending source. A model for saturated sources is not required. We expect the electronic ghost amplitude of a saturated source to deviate substantially from the below-full-well behaviour, also because we won't know the true source flux per pixel. Victim pixels shall simply be masked. Processing tools ---------------- Off-line method Validation ---------- After application to survey data, ideally no cross-talk signal should be visible for unsaturated sources. The S/N can be arbitrarily increased by stacking the ghosts of multiple, unsaturated stars in the same readout channel. The assumption is that the cross-talk amplitude does not depend on location inside a given readout channel. The error from residual cross-talk contributed to source photometry must be smaller than 0.3%. Recovery -------- Should consistent residuals be present in the science data, then the science data can probably be used to update the cross-talk matrices. This would indicate that either the SPR method is not adequate to determine the electronic ghosts from optical sources, or that the cross-talk amplitudes are not stable over time, e.g. due to radiation damage. Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- NISP-P calibration scientist .. raw:: latex \clearpage