.. index:: Photometric large-scale flat (VIS) .. _calobs-vis-large-scale-flats: **CALPRODUCT-VS-013:** VIS Large-Scale Flat =========================================== .. include:: definitions.rst Parent requirement ------------------ | `R-CAL-B-VS-4244 `_ | `R-CAL-B-VS-4245 `_ Scheduling ---------- Monthly Time-critical ------------- No Objective --------- The illumination of the VIS FPA is not expected to be perfectly uniform, due to various factors such as: * Baffle vignetting at the outermost corners of the FPA (LED flats) * An imperfect edge of the M3 mirror * Coating variations on folding mirrors FoM1 and FoM2, far outside the pupil plane, could lead to throughput variations at arcminute scales. * Molecular contamination could cause spatial variation of mirror reflectivities. * The VIS shutter causes uneven illumination (characterized independently through :ref:`calobs-vis-shuttermap`. * Apodization The objective is to reconstruct matching broad-band large-scale flats for VIS from the :ref:`calobs-block-f-selfcal` observations, using stellar photometry. The large-scale flat removes simultaneously any residual large-scale non-uniformity present in the VS-CU flats (:ref:`calobs-vis-prnu`), as well as any large-scale illumination effects from the PLM. Fulfilled by ------------ :ref:`calobs-block-pv-selfcal` :ref:`calobs-block-f-selfcal` Data volume ----------- The same data used for :ref:`calobs-vis-ghostmodel` Processing input ---------------- :command:`Ground Processing Input Data`: BPM :command:`Data Description`: Processing output ----------------- Large-scale flat for VIS. Also produce a coarsely binned (e.g. 100x100, or 256x256) image for trend analysis. Required accuracy, constraints ------------------------------ The VIS large-scale flat reconstructed from a single visit to the Self-cal field must be accurate to better than 0.3%. Processing tools ---------------- OU-VIS Large Scale Flat processing element Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- VIS instrument scientist .. raw:: latex \clearpage