.. index:: Brighter-fatter effect (VIS); Calibration observations .. _calobs-vis-bfe: **CALPRODUCT-VS-004:** VIS Brighter-fatter Effect (BFE) ======================================================= .. include:: definitions.rst Parent requirement ------------------ Not yet in the `CalCD-B `_ Scheduling ---------- Once, during PV. Time-critical ------------- No Objective --------- Increasing amounts of charges in the potential well of a pixel change the physical boundaries of a pixel, effectively shrinking it. Photons arriving from the same source at a late time during an exposure therefore create photo-electrons in a neighboring pixel. This can be recognized by an increase of stellar FWHM with flux, and also by a decrease of pixel-to-pixel variance in flat fields at higher illumination (flattening of the :ref:`calobs-vis-ptc`). The effect directly impacts the PSF models and therefore the shear measurement, and is possibly subject to radiation damage. It is achromatic in nature. Fulfilled by ------------ :ref:`calobs-block-pv-selfcal` (providing stellar field) :ref:`calobs-block-pv-vis-prnu-bfe` :ref:`calobs-block-pv-vis-ptc-cti-eper` (also) :ref:`calobs-block-f-wide-survey` (providing flats) :ref:`calobs-block-f-selfcal` (providing stellar field) Data volume ----------- TBD Processing input ---------------- :command:`Ground Processing Input Data`: :command:`Data Description`: Processing method ----------------- Extrapolate the PRNU to zero value, using the flats at three different fluences. Must take into account that the brighter-fatter effect is modified by charge diffusion and :ref:`charge transfer inefficiency `. Processing output ----------------- BFE kernel for each detector quadrant. Required accuracy, constraints ------------------------------ TBW Processing tools ---------------- TBD Validation ---------- Compare the brighter-fatter kernels with those obtained on ground, and update if necessary. Recovery -------- Update the brighter-fatter model used to correct the PSF and shear data. Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- VIS instrument scientist .. raw:: latex \clearpage