Quality Control and
Data Processing

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

The IRDIS NIR detector is operated in cube mode and in nondestructive readmode (DET.READ.CURNAME=Nondest). All NDIT sub integrations are resolved and are stored in a cube frame with NDIT (~10), NAXIS=3 and NAXIS3=NDIT, meaning a cube frame with NDIT planes of with 2048x1024 pixel. Detector characteristics are monitored via two raw types: DARK, BACKGROUND calibrations. DARK frame calibrations are used to monitor the health of the detector, while BACKGROUND calibrations are used in the cascade to calibrate science data

Dark frames are taken with INS1.OPTI1.NAME=CLOSED to measure the detector dark current, while IRDIS background calibration frames are acquired with INS1.OPT1.NAME=OPEN to measure the instrumental background.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.MEDIANMASTER	sphere_irdis_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.

IRDIS raw dark frame with DIT=30 sec, averaged over NDIT=15 sub integrations.

Trending

IRDIS 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 one HC plot. 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 IRDIS Dark level

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

History

The dark level is stable since begin of operations in 2015-04 (2018-07). There is a slight correlation for the DIT=30sec darks with ambient temperature.

The following table shows the history of pipeline and cpl versions in operation. It is applicable to all QC parameters of any SPHERE arm and mode ingested into the QC1 DB.

Date	event
2015-04-01	pipe: 0.18.0, cpl: 7.0, support:
2015-06-05	pipe: 0.15.0, cpl: 6.6, support:
2016-03-27	pipe: 0.18.0, cpl: 7.0, support:
2017-11-29	pipe: 0.28.0, cpl: 7.0, support:
2018-06-04	pipe: 0.33.0, cpl: 7.1, support: IRDIS photometric standard stars

Algorithm IRDIS 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
QC.MEAN.RON	sphere_irdis_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 IRDIS detector readout noise is monitored for the same three setups as for the dark level.

Scoring&thresholds IRDIS Readout noise

Relaxed thresholds are used for the scoring.

History

From 2017-12-01 on the RON is based on the v0.28 version pipeline recipe. Values are about 1% lower with respect to the pre 2017-12 values obtained froma QC script.

Algorithm IRDIS Readout noise

Before 2017-12: The QC script calculates for each pixel the rms over the sample of NDIT=6..10, meaning of the second five planes of the raw frame cube.

After 2017-12: The readout noise is provided by the pipeline, the algorithm is not documented.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.NUM.HOTPIXELS	sphere_irdis_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 IRDIS Hot pixel number

The scoring thresholds are based on statistical grounds.

History

No remarks.

Algorithm IRDIS Hot pixel number

Pixel deviating more than kappa times sigma the smoothed-version-subtracted-master dark are flagged as hot pixel. The default recipe parameters --ird.master_dark.smoothing=5 and --ird.master_dark.sigma_clip=5 are used.