.. index:: Baseline (NISP); Calibration observations .. _calobs-block-pv-nisp-baseline: **CALBLOCK-PV-014:** NISP Baseline Map ====================================== .. include:: definitions.rst Observation configuration file ------------------------------ | :download:`ocf_CALBLOCK-PV-014.csv ` Scheduling ---------- Executed during commissioning, and repeated 3x during PV, with at least 1 week in between runs. In case of failure, repeat as soon as possible. Time-critical ------------- No Dependencies ------------ None Objective --------- Obtain (and possibly update) the baseline map for all detectors. The baseline has a temperature dependece of approximately -100 ADU/K (decreasing for increasing temperature). It was set for the reference pixels to about 5.5 kADU at a temperature of 89 K (EUCL-IBO-TN-7-039), the science pixels have a set baseline of about 10 kADU. The actual flight temperature will be more like 95 K, i.e. the baseline in flight could be 600 ADU lower than set on ground, which could require an adjustment. The baseline is the bias value for each pixel after reset, affected by kTC noise. The latter is the reset noise caused by freezing thermodynamically created charges in a (disconnected) capacitor. The set pedestial for the reference pixels is about 5500 ADU (+/- 300 ADU), to catch the high variation across pixels and to avoid differential nonlinarity at low values. The baseline map is needed to ensure that the vast majority of all pixels operate in the linear range of the analogue-digital chain. Pixels outside may enter the bad pixel mask. The baseline is assumed to be stable for each up-the-ramp acquisition and therefore removed through ramp fitting (MACC acquisition scheme) or CDS (Fowler-16). In flight, the bias level is calculated from 512 reference pixels for each of the 32 channels, and subtracted in every read before the slope is fit (for the MACC mode). It is known from ground tests that the baseline drifts for about one hour after the detectors are turned on. In this case, the baseline pattern is visible in the darks and even flat-fields. Since during flight we take slew darks on a regular basis, and also have a reference of five raw lines, drifting baselines can be detected. The main objectives therefore are: (1) Verify the value of the baseline (using the median per array). (2) Verify that the distribution of baseline values per pixel is as expected. (3) Verify that the baseline is unchanged, such that the nonlinearity calibration later-on will be applied in the same voltage range of the PReamp+ADC; otherwise, the wrong LUT could be used. To this end, the measurement should be repeated 3x during PV phase. Observations ------------ Observe 64 ramps of MACC(1,16,1) (or MACC(1,16,0) to establish that the baseline has not changed. A single ramp (MACC(1,16,1) will provide an image of the first group with an effective RON of 5 e- after averaging the 16 reads. It is important to reduce the kTC reset noise of the first group image, which after the reference pixel correction is about ``45+/-2`` e-. The reset noise is about :math:`45\pm2 {\rm e}^-`, which will reduce to :math:`5.6 {\rm e}^-` after averaging over the 64 ramps. Spatial dependencies of the kTC noise are not expected. All detectors are read and processed simultaneously. Fulfilling ---------- :ref:`calobs-nisp-baseline` :ref:`calobs-nisp-badpixmap` Targets and pointing constraints -------------------------------- :command:`Pointing`: Straylight suppression as per MOCDA-SYS-003. Instrument configuration ------------------------ NI-FWA closed, NI-GWA RSG000, NI-CU off For reference, see EUCL-IBO-TN-7-039 Methodology / Uplink procedure ------------------------------ :command:`Entity`: NISP :command:`Commanding Method`: NISP: Observation :command:`Dither Sequence`: None Inter-operability constraints ----------------------------- VS-CU off In-orbit duration ----------------- :command:`In-orbit Duration`: 1.5 h (approximate) Approximately ``64*(25s + DPU overhead) = 0.5 h``. A single MACC(1,16,1) exposure takes 25 s (EUCL-IBO-TN-7-039). To be repeated 3x during PV phase. Data volume ----------- ``64*NP = 3584 MB`` per visit. 3 visits in total. The baseline maps have the same compressed size as normal photo-MACC images. Processing input ---------------- :command:`Ground Processing Input Data`: Bad pixel map :command:`Data Description`: Probably the mean and rms baseline maps. Processing method ----------------- If single exposures are downlinked, compute the mean and rms maps after identifying and rejecting cosmics. Processing output ----------------- Baseline maps for each detector. Updated BPM map. Required accuracy, constraints ------------------------------ Pedestal measurement and rms have been successfully obtained. Temporal drifts may have occurred between on-ground and in-flight characterization and must be quantified. Any baseline drifts are expected to be small. Processing tools ---------------- Computation of the median and the RMS of the 64 MACC(1,16,1) images. Further relevant details are spelled out in EUCL-IBO-TN-7-039. Validation ---------- The baseline map is within expectations. Recovery -------- Significant changes in the baseline map are not expected. If they do occur, then likely gradually as a function of increasing radiation damage. Sudden systematic changes in baseline and kTC noise would indicate a significant physical change in the detector chain that warrants a deeper investigation. On board, the baseline is removed by means of the reference pixels and ramp fitting. A change in baseline map therefore has no impact on the flight hardware configuration, but it could affect the nonlinearity calibration. Quality control parameters -------------------------- DataModel: ``_ Contact person -------------- NISP-P calibration scientist .. raw:: latex \clearpage