Quality Control and
Data Processing

HC PLOTS
dark level
readout noise
number of hot pixel
QC1 database (advanced users): browse | plot

The IFS-arm NIR detector is operated in cube mode (NDIT=NAXIS3) and nondestructive readmode (DET.READ.CURNAME=Nondest). All NDIT subintegrations are resolved as NDIT=NAXIS3 planes in a cube with 2048x2048 pixel (times NDIT planes). Detector characteristics are monitored via two raw types: DARK and BACKGROUND calibrations. Only BACKGROUND frames are used to calibrate science data. DARKs are acquired for monitoring the instrumental health.

IFS raw dark frame with DIT=30 sec (any plane of the cube).

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.MEDIANMASTER	sphere_ifs_dark..qc_med	product dark median	HC		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

Trending

IFS dark frames are taken in regular intervals for the following setups

• DIT=2sec, NDIT=40
• DIT=8sec, NDIT=25
• DIT=30sec, NDIT=15

which are trended together in the upper part of one HC plot.

The lower left plot shows the linear relation between the dark level and the exposure time. The marked relation of dark level(DIT) = -6 +10.2 * DIT refers to the relation for T_bench=16 deg.

The lower central plot shows the values of the IFS bench temperature sensor with time.

The lower right plot monitors the relation between the dark level and the bench temperature for the three mentioned setups.

In addition dark frames are also acquired with the DIT and NDIT of the science observations.

The darks come as a single frame with one cube (NAXIS=3).

Scoring&thresholds IFS Dark level

The dark levels are scored for three setups, relaxed thresholds have been chosen.

History

• The dark level and its relation with DIT and T_bench is stable since the begin of operations (2018-07-20).
• From 2015-04-01 until 2017-05, IFS dark frames with DIT=1.650726 (and other of higher DIT) show persistence, in particular the first low-DIT dark exposure of the night is affected, others acquired later during the day-time calibration sequence are not affected. The pattern looks like an imprint of the IFU flat. The persistence is monitored in a dedicated HC plot. It is recommended to use IFS background calibrations for the mentioned period. The following image shows an affected DIT=1.650726 dark, the unaffected DARK with the same setup has been subtracted.

  Persistence in IFS dark.

• 2019-02-16: The first set of IFS_DARK at 17T12 with T_det=94K shows significant deviations in level, ron and hotpix.
  The second set of IFS_DARK at 17T10 with T_det=90K shows ron and level ok, and only more hotpix.
  Reference/nominal T_det=82K.

Algorithm IFS Dark level

The pipeline uses the median dark level of the raw frame cube in ADU.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
[derived by a QC procedure]	sphere_ifs_dark..qc_ron	product ron	HC		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

Trending

The IFS detector readout noise is monitored for the same three setups as for the dark level in the upper part of the plot.

The lower left box shows the relation between statistical noise and exposure time DIT. The marked square root law of RON(DIT) = 2.47 + sqrt(-6 + 10.2 * DIT / 3.6) means that the static detector noise is 2.47 ADU and the measured RON is contaminated by photon noise sqrt(counts / gain) induced by the dark current ( = -6 + 10.2 * DIT).

The lower central plots shows IFS T_bench temperature values

Scoring&thresholds IFS Readout noise

The three reference setups (DIT=2, 8, and 30) are scored according to the dashed lines in boxes 1,2, and 3. All other setups are scored according to the non-linear arithmetic relation indicated by the dashed curves in box 4.

• upper threshold = sqrt((-6 + 10.2 * DIT)/3.6)+2.47 -2.0-0.1*DIT
• lower threshold = sqrt((-6 + 10.2 * DIT)/3.6)+2.47 +3.0+0.1*DIT

History

No remarks.

Algorithm IFS Readout noise

From the raw frame fits cube, five planes are extracted (plane 6 to 10), and for each pixel the stdev (out of five independent reads) is calculated. The median over all pixels stdev is taken.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.NUM.HOTPIXELS	sphere_ifs_dark..qc_hotpix		HC		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

Trending

The number of hot pixel is monitored for the same three setups are for the dark level and the ron.

Scoring&thresholds IFS Hot pixel number

The scoring thresholds are based on statistical grounds.

History

No remarks.

Algorithm IFS Hot pixel number

A smoothed version of the master dark is subtracted from the master dark to eliminate background gradients. Pixel which deviate more than 5 sigma from the difference product are flagged as hot pixel.