.. index:: Charge transfer inefficiency (CTI); Calibration observations .. _calobs-vis-cti-cil: **CALPRODUCT-VS-005:** VIS CTI Charge Injection Lines ===================================================== .. include:: definitions.rst Parent requirement ------------------ | `R-CAL-B-VS-4351 `_ | `R-CAL-B-VS-4352 `_ | `R-CAL-B-VS-4354 `_ | `R-CAL-B-VS-4355 `_ | `R-CAL-B-VS-4356 `_ | `R-CAL-B-VS-4357 `_ | `R-CAL-B-VS-4358 `_ Scheduling ---------- Execute the full sequence six times at the beginning of the PV phase. Execute once every 1.5 ~ 2 weeks, during the PV phase. Daily, as part of the ROS. Time-critical ------------- No Dependencies ------------ None Objective --------- Radiation damage will increase the degree of Charge Transfer Inefficiency (CTI) in the VIS CCDs. The CTI is corrected for in the VIS science images using a calibrated CTI model. This ``CalProduct`` provides the CTI model, based on charge injection line (CIL) data and flat fields taken during PV phase, and continuously as part of the ROS. Observations ------------ **PV phase CIL parameters** The PV phase CTI calibrations (sequence of 42 CIL patterns) are in addition to the ROS (sequence of 32) seen here, and are defined in :ref:`calobs-block-pv-vis-cti-charge-injection`. **ROS charge injection line (CIL) parameters** 8 charge injection line (CIL) images are taken daily during the nominal survey, along with flat-field images, to calibrate the continuously increasing level of CTI. **Constant CIL parameters (ROS):** * VSTART_CHG_INJ = 16 * VEND_CHG_INJ = 2066 * VSTART = 0 * VEND = 2086 .. csv-table:: **Variable CIL parameters (ROS).** :download:`CSV file ` :widths: auto :file: tables/cti_ros.dat Fulfilled by ------------ :ref:`calobs-block-pv-vis-cti-charge-injection` :ref:`calobs-block-pv-vis-cti-timingsequence` :ref:`calobs-block-f-wide-survey` Targets and pointing constraints -------------------------------- None Instrument configuration ------------------------ Instrument: Wide survey Methodology / Uplink procedure ------------------------------ :command:`Entity`: VIS :command:`Commanding Method`: VIS :command:`Dither Sequence`: ROS Inter-operability constraints ----------------------------- None Data volume ----------- ``192*VB = 48000 MB`` (PV phase) ``8*VB = 2000 MB`` (per day, during nominal survey) Processing input ---------------- :command:`Ground Processing Input Data`: :command:`Data Description`: Processing method ----------------- The charge injection and flat field images are bias and NL corrected. A CTI model is then fitted using the VIS_CTI PE, which is performed a nonlinear search using the nested sampling algorithm MultiNest. Processing output ----------------- Updated parameters on the CTI model for that given observation data (.json of best fit parameters is stored via the DataModel). Additional information and metadata on the model-fit (e.g. nested sampling samples, summary statistics). Required accuracy, constraints ------------------------------ | `R-CAL-B-VS-4351 `_ | `R-CAL-B-VS-4354 `_ | `R-CAL-B-VS-4355 `_ | `R-CAL-B-VS-4356 `_ | `R-CAL-B-VS-4358 `_ The CTI model used to correct CTI in the VIS detectors must correct CTI to better than :math:`4.0\times10^{-3}` (TBC). Processing tools ---------------- VIS_CTI PE Validation ---------- * Reduced chi-squared of CTI calibration pipeline model-fit is close to 1. * Use CTI correction algorithm on charge injection data and check that residual EPER trails produce spurious ellipticity below 1.0e-4 using equation (14) of Israel et al 2015 (https://arxiv.org/abs/1506.07831). Recovery -------- * Update the CTI calibration model. Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- VIS instrument scientist .. raw:: latex \clearpage