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VISIR Quality Control:
DARK frames

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read-noise | dark level | det. temperature
 
QC PLOTS
  CURRENT HISTORY
read-noise
read-noise12
dark level
temperature
QC1 database (advanced users): browse | plot
   Click on CURRENT to see the current trending (Health Check).
   Click on HISTORY to see the historical evolution of the trending.


One DARK frame for the imaging and one DARK frame for the spectroscopic detector is taken every day within the VISIR daytime calibrations. Each DARK consists of 3 raw frames and is always obtained with the same instrument setup - detector integration type (DET.DIT)=0.02s and the number of detector sub-integrations (DET.NDIT)=1000. The DARK frames are not used for calibrating science data. They are utilized only to monitor performance of the VISIR's detectors.

DARK frame of the imaging detector . This is a master DARK frame which is a pipeline product of the "visir_img_dark" recipe. It was build by averaging the 3 raw frames. Note bright horizontal stripes which are characteristic for this type of the detector. Also visible are clusters of bad pixels. DARK frame of the spectroscopic detector. This is a master DARK frame which is a pipeline product of the "visir_img_dark" recipe. The same recipe is used for combining darks of the imaging and spectroscopic detectors. It was also build by averaging the 3 raw frames. Here, characteristic stripes are vertical

Other VISIR detector parameters that are monitored:
number of bad pixels detectors

top read-noise

The following plot shows the temporal evolution of the read-out noise for both imaging (panel 1) and spectroscopic (panel 2) detectors. The plotted values correspond to the read-out noise calculated from the 3rd-2nd raw frame in the stack. On the other hand the read-noise12 plot monitors the same parameter calculated from difference of 2nd-1st. It's been noticed that the 1st dark raw frames of the stack are contaminated by a transient feature that artificially increases the background level. The feature seems to disappear already in the 2nd and 3rd frame, so they better correspond to the real state of the detectors.

QC1 parameters

  • read noise (QC1 database table visir_dark_img, visir_dark_spc, column ron2)
    This is the read-out noise calculated from the 3rd-2nd raw. It is a median of the standard deviations measured from 100 4x4 windows on the difference frame, multiplied by sqrt(NDIT/2). The read-out noise values are calculated the same way for both imaging and spectroscopic detectors.
  • read noise12 (QC1 database table visir_dark_img, visir_dark_spc, column ron1)
    This is the read-out noise calculated from the 2nd-1st raw. It is a median of the standard deviations measured from 100 4x4 windows on the difference frame, multiplied by sqrt(NDIT/2). The read-out noise values are calculated the same way for both imaging and spectroscopic detectors.
top dark level

QC1 parameters

  • dark level (QC1 database table visir_dark_img, visir_dark_spc, column darkmed)
    The median dark level is calculated in the central part of the master dark.
top det. temperature

The following plot shows the temporal behavior of the temperature of the imaging (panel 1) and spectroscopic (panel 2) detectors. The plotted values correspond to the readouts of the cold fingers in the VISIR's cryostat. The temperatures written in the header keyword INS.SENS30.VAL are the closest to the imaging detector and the once in the keyword INS.SENS31.VAL to the spectroscopic detector.

QC1 parameters

  • det. temperature (QC1 database table visir_dark_img, column ins_sens30_val and QC1 database table visir_dark_spc, column ins_sens31_val)

 
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