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VISIR Quality Control:
FLAT FIELD frames

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   Click on CURRENT to see the current trending (Health Check).
   Click on HISTORY to see the historical evolution of the trending.


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 The information on this page refers to the pre-upgrade status until May 2012 and is kept here for historical reference.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

Flat-field frames are obtained both with the imaging and the spectroscopic detector.

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. 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 K.

top nbadpix

QC1 parameters

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 are flagged as bad pixels.

parameter QC1 database: table, name procedure
bad pix visir_flat_img, nbbadpix
visir_flat_spc, nbbadpix
The number of pixels for which the relative gain falls outside the range from 1/5 to 5.

Trending

The number of bad pixels is trended separately for both the imaging and the spectroscopic detector.

History

April 2015: start of operations after upgrade with new detectors

top flat-field flux

QC1 parameters

This parameter monitors the stability of the Warm Calibration Unit (WCU). The first two flat-field frames in the stack (taken at temp. 20C and 10C of the WCU) are subtracted from each other, the median flux in the central area is calculated, and normalized by DIT.

parameter QC1 database: table, name procedure
lamp_flux visir_flat_img, lamp_flux The flux difference of the flat-fields taken at 20C and 10C.

Trending

The flat-field flux is trended for the imaging detector.

History

April 2015: start of operations after upgrade with new detectors


 
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