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FORS2 Quality Control:
Detector Parameters

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conversion factor | fixed-pattern noise
 
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conversion factor
fixed-pattern noise
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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.


Parameters are measured for the 5 standard filters BVI Bessell and UR_Special, and for the standard CCD modes (100Kps/high_gain/2x2 and 200Kps/low_gain/2x2).

top Conversion Factor

QC1 parameters

  • conversion factor (1/gain) (QC1 database table fors2_scrflat, column conad)
    If the exposure time of the first two raw screen flat fields in the input set of frames is the same (within 4%), the difference frame is computed, which is then divided by 2 and by the first input frame. This frame estimates the gain in ADU/e- at each pixel and the conversion factor in e-/ADU is calculated as the reciprocal mean of this frame.

History

  • 2010-11-04 - 2010-12-01 The flat field lamp saturates the screen flats. Therefore there are no valid data for that time range.
  • The old pipeline in use until 2008-03-31 derived the CONAD somewhat differently: the whole readout port was divided into a chessboard of 16x16 boxes. For each one of these boxes, the median signal level from the first raw frame was divided by the variance in the difference frame scaled by 2. The median value of the 16x16 values obtained was the accepted value for the conversion factor.
  • For the old FORS2 CCD (until March 2002) the conversion factor was derived from a raw file as 100x100 pixels sigma, corrected for fixed-pattern contribution. The sigma was compared to the square-root of the signal averaged across 4 ports. The conversion factor was trended only for the R_SPECIAL filter.
top Fixed-Pattern Noise

QC1 parameters

  • relative fixed-pattern noise (QC1 database table fors2_scrflat, column FPN_rel)
    The fixed-pattern noise is computed in the following way: The difference of two 100x100 sub-frames of the same master flat field image is determined. These two sub-frames are are shifted with respect to each other by 10 pixels in X- and Y-direction. The population standard deviation of the difference frame, divided by the square root of 2, minus the photon noise (geometrically subtracted) yields the fixed-pattern noise, which is then divided by the median of the respective region. The fixed-pattern noise is dominated by the brick wall like pattern shown by the MIT-CCDs, that is particularly strong in U and is due to the CCDs thinning procedure. It is trended only for the B_BESSELL filter.

History

  • 2010-11-04 - 2010-12-01 The flat field lamp saturates the screen flats. Therefore there are no valid data for that time range.
  • For the old FORS2 CCD (until March 2002) trending of the fixed-pattern noise can be found here.

 
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