.. index:: Spectroscopic large-scale flat (NISP) .. _calobs-nisp-spec-large-scale-flats: **CALPRODUCT-NS-004:** NISP-S Large-Scale Flat ============================================== .. include:: definitions.rst Parent requirement ------------------ Not yet in the `CalCD-B `_ Scheduling ---------- Monthly Time-critical ------------- No Dependencies ------------ None Objective --------- Reconstruct matching spectroscopic large-scale flat fields for all four grisms from the :ref:`calobs-block-f-selfcal` observations. Fulfilled by ------------ :ref:`calobs-block-pv-selfcal` :ref:`calobs-block-f-selfcal` Data volume ----------- TBD Processing input ---------------- :command:`Ground Processing Input Data`: BPM :command:`Data Description`: Processing method ----------------- By comparing fluxes of small chunks of wavelengths in stellar spectra from a set of widely dithered pointings, a large-scale illumination correction is calculated. This calibration removes simultaneously the large-scale non-uniformity present in the NI-CU beam (:ref:`calobs-nisp-led-flats`) as well as any vignetting effects from the telescope and instrument optics (NI-CU illuminates the focal plane array directly, without passing through any optics). The exact procedure is TBW. In principle, the same code as for the :ref:`calobs-nisp-phot-large-scale-flats` can be used, once the fluxes of the spectral fragments have been extracted. Processing output ----------------- Large-scale flat fields for all grisms. Trend analysis. Required accuracy, constraints ------------------------------ TBD Processing tools ---------------- Large-scale flat-field pipeline Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- NISP-S calibration scientist .. raw:: latex \clearpage