VISIR: Flat-field frames
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HC PLOTS |
Number of bad pixels |
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Flat-field flux |
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QC1 database (advanced users):
browse |
plot
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Flat-field frames are not measured any longer after the instrument upgrade.
The information on this page refers to the pre-upgrade status until May 2012
and is kept here for historical reference.
One set of flat-field exposures is taken daily during daytime. It consists of
up to 6 raw frames, where each is illuminated with different flux level. The
changes of the flux are achieved by illuminating the detector with the Warm
Calibration Unit which simulates black body radiation with different
temperatures:
- 1st frame: 20 C (keyword INS.EXTS.ACT)
- 2nd frame: 10 C
- 3rd frame: 0 C
- 4th frame: -10 C
- 5th frame: -20 C
- 6th frame: -30 C
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FLAT FIELD master frame of the imaging detector (pre-upgrade). This is a pipeline product of the visir_img_ff recipe. It was build by combining the 6 input raw frames. Note bright horizontal stripes which are characteristic for the pre-upgrade detector.
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FLAT FIELD 2nd raw frame (pre-upgrade). This is a 2nd raw FLAT FIELD frame which corresponds to the illumination by the black body with temperature of 10 C.
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Bad pixels
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.NBBADPIX | visir_flat_img..nbbadpix | number of bad pixels | HC | | [docuSys coming] |
QC.NBBADPIX | visir_flat_spc..nbbadpix | number of bad pixels | 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 bad pixels was trended separately for both the imaging and the
spectroscopic detector.
Scoring&thresholds Bad pixels
Scoring is not implemented.
History
May 2012: end of operations new detectors, flat fields are no longer measured.
Algorithm Bad pixels
The median intensity is determined determined for each flat-field image. Then
a linear fit of the actual intensity per pixel and the median is achieved.
Those pixels where the slope (i.e. relative gain) deviates strongly from 1,
i.e. the relative gain is outside the range of 1/5 to 5,
are flagged as bad pixels.
Bad pixels
QC1_parameters
FITS key |
QC1 database: table, name |
definition |
class* |
HC_plot** |
more docu |
QC.LAMPFLUX | visir_flat_img..lamp_flux | lamp flux per DIT | CAL | | [docuSys coming] |
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one. |
Trending
The flat-field flux was trended for the imaging detector.
Scoring&thresholds Bad pixels
Scoring is not implemented.
History
May 2012: end of operations new detectors, flat fields are no longer measured.
Algorithm Bad pixels
This parameter monitors the stability of the Warm Calibration Unit (WCU). The
first two flat-field frames in the stack (taken at temperatures 20C and 10C of the
WCU) are subtracted from each other, the median flux in the central area is
calculated, and normalized by DIT.
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