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GIRAFFE Quality Control:
DARK frames

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Trending & QC1
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QC links:
dark level | glow
DARK current
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.

2008-05-24: new GIRAFFE CCD "Carreras" operational (replacing "Bruce"), find documentation for the old and the new CCD here.
Both CCDs are identical in format and size; unless otherwise specified, the content below applies to both CCDs.

2010-01-05: description for new CCD added

A set of 3 DARK frames is measured approximately once per month. These frames are combined and debiassed. The DARK current is monitored. The most prominent feature in the dark of the old CCD is the glow in the upper right. It is caused by illumination by a faint diode and appears on all frames with longer exposure times, in particular on science frames. Note that the glow strength, as well as the dark level, vary slowly in time, but sometimes suddenly after an intervention. Between 2003-07 and 2004-07-26, there has been no glow at all! If you are concerned about careful background correction, you should remove the dark signal with a master dark close in time with the science data.

The new CCD has no such feature and does not require master dark subtraction.

DARK frame, old CCD. The dark current as seen in a master DARK frame. The dark shown here is simply summed from 3 input frames. These are taken roughly once per month and have 1 hour integration time each. The pipeline generates a stack which is cleaned from the numerous cosmics.

This example refers to the old CCD ("Bruce") with the strong glow.

The new CCD ("Carreras") has a very low and uniform dark, in particular no glow.

Find other detector parameters documented here:
bias parameters bias
detector parameters like gain, contamination etc. detector

top DARK level

Box 1 of the trending plot shows the DARK level measured across a central window, excluding the glow. The value in the plot is the dark current and is given in ADU per hour per pixel. Note that the DARK level is slowly varying with time.

QC1 parameters

parameter QC1 database: table, name procedure
"DARK_current": mean dark level (ADU/hr/pixel) giraffe_dark..current_dark mean of master_dark, measured in a central window
total exposure time, in sec giraffe_dark..exptime total exposure time for all darks, in sec.
number of input raw frames giraffe_dark..datancom number of input frames combined in master_dark


The median bias level is plotted in box 1 of the trending plot.


There is a trending plot covering the full DARK history (here). The mean dark has evolved over the years. For data reduction (glow removal), a master_dark not too far in time should be chosen.

top Glow

This applies to the old CCD only. Box 2 of the historical trending plot (2008 and before) measures the strength of the glow pattern. The flux is summed in a window centered on the glow (ADU per hour).

The QC1 database for dark frames also stores the X and Y positions of the glow.

QC1 parameters

parameter QC1 database: table, name procedure
"GLOW": strength of glow giraffe_dark..glow_dark measure the strength of the glow feature (sum of all counts in region X1400..2048, Y 3800..4096), in ADU per hour.
X position of glow maximum giraffe_dark..glow_posx find maximum of glow, measure its X and Y position
Y position of glow maximum giraffe_dark..glow_posy


The trending plot covering the full DARK history (here) shows that the strength of the glow was slowly varying with time (old CCD). It was completely absent between 2003-07 and 2004-07-26.

The new CCD used since 2008-05-26 has no glow.