SPHERE: IRDIS Dark
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HC PLOTS |
dark level |
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readout noise |
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number of hot pixel |
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QC1 database (advanced users):
browse |
plot
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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.
IRDIS Dark level
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. |
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IRDIS raw dark frame with DIT=30 sec, averaged over NDIT=15 sub integrations.
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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.
IRDIS Readout noise
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.
IRDIS Hot pixel number
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.
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