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noise parameters | dark level
noise parameters
dark 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 Daily Health Check templates for darks acquire each day dark frames of the following setups:
  • Hawaii-array (SW) DoubleCorr (imaging) DIT=10
  • Hawaii-array (SW) NonDest (spectroscopy) DIT=10
  • Aladdin-array (LW) DoubleCorrHighBias DIT=0.28 and DIT=0.56
  • Aladdin-array (LW) DoubleCorrLowBias DIT=2 and DIT=5
  • Aladdin-array (LW) UncorrHighBias DIT=0.11
top noise parameters

We consider the noise in dark frames to be composed by statistical noise (random noise) and fixed pattern noise. Close to the read-out ports there might be contributions of photon noise as well. If a raw dark frame has DIT=5sec and NDIT=10, this means that 10 times 5-sec exposures have been averaged on the array before the read-out occurred. The statistical noise as derived from a raw frame is reduced to NDIT=1 via sqrt(NDIT) to be comparable to other dark settings. The fixed pattern noise does not vary with NDIT by definition.

QC1 parameters

parameter QC1 database: table, name procedure

random noise

(the shared plot shows:
random noise,
dark level and
dark level rms)

ron12, ron23,
qc_UL_ron12, qc_UL_ron23,
qc_UR_ron12, qc_UR_ron23,
qc_LL_ron12, qc_LL_ron23,
qc_LR_ron12, qc_LR_ron23
- for the Hawaii array QC.RON parameters are given for each quadrant separately, while the Aladdin array frames give only one QC.RON parameter for the whole chip. The pipeline subtracts two raw frames and takes a number of random samples, derives the stdev, and takes the median stdev. These values are trended for the most frequently used DITs. The recipe gives two RON values, since the measurement is applied to the first and second pair of consecutive pair of raw dark frames. The second RON value is an independent measurement, except for LW Uncorr setting, where the second measurement gives a RON about 2 ADU less than the RON derived from the first two raw dark frames.
fixed-pattern noise isaac_dark, qc_UL_fpn, qc_UR_fpn, qc_LL_fpn, qc_LR_fpn - since 2006 a Gaussian fit to the histogram of the MASTER_DARK product is performed and the resulting width defines the FPN. This version is independent on sporadic changes of the hot pixel distribution. The histograms usually show a single peak, but for the LW Uncorr setting, two quadrants of the detector show a multivariate distribution of three peaks. In this more complex case the FPN gives the again the width of the fit of a single Gaussian to the multivariate histogram, although the fit quality is worse.
standard deviation isaac_dark, qc_UL_stdev, qc_UR_stdev, qc_LL_stdev, qc_LR_stdev - for each quadrant (512x512 pixel area) of a MASTER_DARK product frame the central 100 x 100 pixel area is selected. The eclipse command stcube is used for this QC1 parameter. It turns out that the values (it is an unclipped sigma) are dominated by the number and the strength of hot pixels. This parameter is suitable to monitor changes in the hot pixel structure.
robust random noise isaac_dark, qc_n_gaf - this measurement is the width of the Gaussian fit to the random noise histogram. This means the Gaussian is fit to the histogram of the difference of two raw dark frames. An improved iterative fitting routine is used since 2006 to gain greater robustness. The value is an independent cross check for the pipeline delivered random noise value.

top dark level

QC1 parameters

parameter QC1 database: table, name procedure
dark level isaac_dark, qc_darkmed - is taken from each product frame and is trended. The parameter is the median of the MASTER_DARK product frame
dark level rms isaac_dark, qc_dark_stdev - the dark medians within a set of three coherent raw dark frames is measured. The stdev of the three raw frame median is taken. It is a measure of the short-term stability of the dark level at a given DIT


Some of the QC1 parameters are related with each other. We check the stability of this QC1 parameter relation and simply plot QC1_A versus QC1_B in a diagram. The relation is hence defined empirically, although it is possible to define a theoretical relation as well. Such a diagram shows the relation based on values collected of a longer period of time. The current (the newly extracted) QC1 parameters are overplotted over this relation using another graphical coding, to highlight them.

  • Median Dark Level versus DIT, or sometimes called the reset-anomaly is a relation given by the architecture of the multiplexer. The reset-anomaly is a function of the temperature and the read-out speed of the array. The trending of this relation is given for our 5 setups
  • Fixed pattern noise versus Median Dark Level, (here again the high frequency component, not cleaned for hot pixels, bad pixels and low contribution of statistical components as read noise and photon noise) should be mostly linear in the low flux level regime. The trending of this relation (red points) as well as the random noise which should be independent on DIT and hence the median dark level (green points) is given for our 5 setups
  • Read out noise versus DIT shows a minor dependence on DIT.


  • 2007-06-26 to 2007-07-01: intervention; DARK current from 310 to 360 ADU for DIT=10sec
  • 2007-07-19 to 2007-07-30: intervention;
  • 2007-08-11 power cut and UPS off, T=150K;
  • 2007-09-30 to 2007-10-06 intervention;
  • 2007-10-24 to 2007-11-04 intervention;
  • 2008-02-03: (UT=10..23) OddEvenColumnEffect increased from 0.004 to 0.02;
  • 2008-02-25 Hawaii: DET.RSPEED changed from 6 to 10;
  • 2008-02-29 Hawaii: detector warmed up by intension and cooled again;
  • 2008-04-21 to 2008-04--28 intervention for M7 and odd-even column effect;
  • 2008-04-28 to 2008-05--04 recovery;
  • 2008-05-04 Hawaii: DET.RSPEED changed from 10 to 6;
  • 2008-05-08: recovery finished;
  • 2009-12-20: after intervention dark level dropped by few percent for all detector modes;
  • 2011-04-10 Hawaii: readout speed changed to deal with a new case of the odd-even column effect
  • 2011-05-17 Hawaii: problem with the Hawaii (SW) detector; signal in the UL quadrant gone
  • 2011-06-13 Hawaii: intervention to replace/fix the Hawaii detector started
  • 2012-06-18 Hawaii: read speed changed from 4 to 6, to deal with the odd-even-column effect
  • 2012-06-26 Hawaii: read speed further changed from 6 to 10, to deal with the odd-even-column effect
  • 2012-07-22 Hawaii: read speed changed to 4; the odd-even-column effect disappeared