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CURRENT 
HISTORY 
effective nonlinearity and maximum exposure level 


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. 
The CRIRES detector arrays become nonlinear for exposure
levels above about 4000 ADUs. This behaviour is assessed by a series of
dark and flat exposures with increasing DIT which maps in the flats the
gain behaviour from the linear to the nonlinear regime. After dark subtraction,
the function
ADU =
A + B * DIT + C * DIT^2
is fitted for each pixel of the flat sequence. The coefficients
A, B, and C are saved into an output cube, which can be converted into individual frames. Above about 12000 ADUs, a quadratic fit is not
sufficient any more. Such exposure levels should, therefore, be avoided.
The application of the coefficient images to correct science
frames is described on the science
recipe pages.

Example fit. A fit
of the increasing flux for a single pixel (x=511, y=256). The measured
values are plotted as blue circles. The red line is a linear fit
to the first two exposures; the green line a quadratic function
with A = 29, B = 787, and C = 2.5. Both fits begin to differ above
about 4000 ADU.


Example frame for A coefficients.
Enlargement of the centre region of an image of the A coefficients.


Example frame for B coefficients.
Enlargement of the centre region of an image of the B coefficients.
These coefficients show the pixeltopixel gain variation in the
linear regime which can be corrected by flatfielding.


Example frame for C coefficients.
Enlargement of the centre region of an image of the C coefficients.
These are the remaining pixeltopixel gain variations in the nonlinear
regime.

QC1 parameters
QC1 parameters for
CRIRES flatfield exposures are measured for each detector array separately.
parameter 
QC1 database: table, name

procedure 
mean effective nonlinearity 
crires_detmon, lineff 
difference between the flux obtained at reference level from the polynomial fit and the flux predicted by the linear term only, normalized by the polynomial flux 
reference level for lineff 
crires_detmon, reflevel 
none (userdefined) 
maximum exposure level 
crires_detmon, counts_max 
mean exposure level of flat frame with highest DIT 
Trending
The effective nonlinearity and the maximum exposure level are trended.
