How well can charge transfer inefficiency be corrected? A parameter sensitivity study for iterative correction

Abstract

Radiation damage to space-based Charge-Coupled Device (CCD) detectors creates\ndefects which result in an increasing Charge Transfer Inefficiency (CTI) that\ncauses spurious image trailing. Most of the trailing can be corrected during\npost-processing, by modelling the charge trapping and moving electrons back to\nwhere they belong. However, such correction is not perfect -- and damage is\ncontinuing to accumulate in orbit. To aid future development, we quantify the\nlimitations of current approaches, and determine where imperfect knowledge of\nmodel parameters most degrade measurements of photometry and morphology. As a\nconcrete application, we simulate $1.5\\times10^{9}$ "worst case" galaxy and\n$1.5\\times10^{8}$ star images to test the performance of the Euclid visual\ninstrument detectors. There are two separable challenges: If the model used to\ncorrect CTI is perfectly the same as that used to add CTI, $99.68$ % of\nspurious ellipticity is corrected in our setup. This is because readout noise\nis not subject to CTI, but gets over-corrected during correction. Second, if we\nassume the first issue to be solved, knowledge of the charge trap density\nwithin $\\Delta\\rho/\\rho\\!=\\!(0.0272\\pm0.0005)$ %, and the characteristic\nrelease time of the dominant species to be known within\n$\\Delta\\tau/\\tau\\!=\\!(0.0400\\pm0.0004)$ % will be required. This work presents\nthe next level of definition of in-orbit CTI calibration procedures for Euclid.\n