QC PLOTS
	LAST	HISTORY
conversion factor
fixed-pattern noise
QC1 database (advanced users): browse | plot
Click on CURRENT to see the current (last) trending (Health Check).    Click on HISTORY to see the historical evolution of the trending.

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

QC1 parameters

• conversion factor (1/gain) (QC1 database table fors1_scrflat_2CCD, 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. 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.
• relative fixed-pattern noise (QC1 database table fors1_scrflat_2CCD, 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 wave like pattern shown by the CCDs, that is particularly strong in U and is due to the CCDs' thinning procedure. It is trended only for the R_BESSELL filter.
  

History

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.