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VIMOS Quality Control:
bias frames

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bias level | read-out noise | structure
 
QC PLOTS
  CURRENT HISTORY
bias level
bias rms
bias ron
averages low gain
averages high gain
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.


Bias frames are usually measured daily in two read-out modes:

  • low gain, 1x1 binning, 2148x2440, used for imaging,
  • high gain, 1x1 binning, 2148x4096, used for spectroscopy.

All QC parameters are computed in the central 1600x1800 pixels of each CCD.

top Bias level

QC1 parameters

parameter QC1 database: table, name procedure
median bias level vimos_bias, median_master median level of master bias product (which is the median of five input frames)

Trending

The bias level is trended for each quadrant and for each read-out mode separately. There are also plots that show the average and the standard deviation across all four quadrants as a quick overview of the global behaviour.

History

July 2010: new detectors, bias level around 2500 ADU; the bias level varies with temperature, especially for quadrant 2
2011-02-21: bias level adjusted to 200 ADU on all quadrants
2011-05-19: UV flooding of Q2 detector, bias level increased by 20 ADU

top Read-out noise

QC1 parameters

parameter QC1 database: table, name procedure
read-out noise vimos_bias, ron_bias read-out noise (ron) is measured as the standard deviation divided by sqrt(2) of the difference between the first two raw frames in a bias stack

Trending

Read-out noise is trended for each quadrant and for each read-out mode separately. There are also plots that show the average and the standard deviation across all four quadrants as a quick overview of the global behaviour.

History

July 2010: new, thicker detectors, read-out noise measurement is strongly affected by cosmic ray hits; scoring disabled

top Structure

QC1 parameters

parameter QC1 database: table, name procedure
rms vimos_bias, rms_master standard deviation of the master bias product; gives information on the combined noise and structure components
fpn vimos_bias, fpn_master fixed-pattern noise (fpn) of master bias: mostly an indicator of the presence of hot-columns. The computation of this parameter is done by creating a shifted (by 10x10 pix) version M' of the master M and calculating the RMS of the difference frame M -M'. This is the combination of small-scale noise and white noise (scaled by sqrt(2)). The white noise contribution is then quadratically subtracted from the total noise.
structure vimos_bias, struc_master indicator of noise components with scales larger than 10 pixels. It is an indicator for gradients but it is strongly contaminated by the presence of hot-columns. The population standard deviation of the master bias is computed (parameter RMS). This is the combination of large scale structure, small scale structure, and white noise. The white noise and the small scale structure contributions are then quadratically subtracted.

Trending

RMS is trended for each quadrant and for each read-out mode separately. FPN and structure are only plotted as averages across all four quadrants.

 


 
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