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VIRCAM Quality Control:
Darks

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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:
  • NCORRS=Double, NDIT=1, DIT=1.001100
  • NCORRS=Double, NDIT=1, DIT=120.000000

The Calobuild templates acquires dark frames for each detector setup used for science OBs of the preceding night.

top dark level

QC1 parameters

parameter QC1 database: table, name procedure
qc_darkmed vircam_dark, qc_darkmed - QC.DARKMED is the median of the MASTER_DARK pipeline product frame.
REFERENCE_DARK parameters vircam_dark, qc_darkdiff_med, qc_darkdiff_rms - For the QC.DARKDIFF_MED, a reference master dark ( PRO.CATG = REFERENCE_DARK ) is subtracted from the current master dark. The median and the robust noise, using MAD, of the difference frame is given


The relation between the dark level and the DIT is given in the following plots.

Each Fig. shows the relation: dark level versus DIT for four detectors aligned in a row. Note the particular reset anomaly of detector #13.

There occurs a further subtle effect: Each NDIT adds about 12 ADU to the dark level. And each NDIT adds 1 ADU to the statistical noise. This means: A raw frame acquired with DIT=10sec and NDIT=5 has 60 ADU more signal and 5 ADU more statistical noise than a raw dark frame with DIT=50 sec and NDIT=1.

top noise parameters

QC1 parameters

parameter QC1 database: table, name procedure

darkrms

vircam_dark, qc_darkrms
- The QC.DARKRMS is a measure of RMS obtained from MASTER_DARK frames in ADU. It is the median of the absolute deviations from the median ( = MAD ) times 1.48.
cosmic particle rate vircam_dark, qc_particle_rate - The QC.PARTICLE_RATE is the average number of pixels rejected during frame combination. The number of rejected pixel is decreasing with increasing DIT, meaning the parameter is not an estimate of the cosmic ray hits.
striperms vircam_dark, qc_stripe_rms - Raw dark frames show an additive pattern of horizontal stripes, which is varying on a short term and in strength (~ +- 5-20 ADU). RMS of the stripe pattern is monitored.
hot pixel vircam_dark,
qc_nhotpix, qc_hotfrac
- QC.NHOTPIX is the number of detected hot pixels. A pixel is considered hot, when more than 2 of 5 raw input frames deviate from the mean. So far the qc_nhotpix are the number of deviant pixel. The threshold --thresh is a pipeline recipe command line parameter. QC.HOTFRAC is the fraction of hot pixels = QC.NHOTPIX / (2048 * 2048)

The darkrms QC parameter measures the structural noise or fixed pattern noise in a master dark pipeline product. Only in detector #13 with its strong reset-anomaly, the nearly linear relation between the darkrms and the darkmed parameters ( = between the structural noise and the counts) is established. For all other 15 detectors with negligible reset-anomaly, the darkrms is rather constant within the small range of recordable darkmed values.

Figure caption:
Upper left: darkrms QC parameter against darkmed for VIRCAM detector #13. Data are based on VIRCAM master darks taken between 2010-05-03 and 2010-08-03 with NDIT=1.
Upper left: darkrms QC parameter against darkmed for VIRCAM detector #10.
Lower left: darkrms as function of DIT (NDIT=1) for detector #13. As darkrms is linearly related with darkmed, this Fig. shows the dominating reset-anomaly of detector #13.
Lower right. darkrms as function of DIT (NDIT=1) for detector #10 as a representative for other detectors (excpet #13). The variation of darkrms over DIT is negligible, a consequence of the reset anomaly.


top secondary parameters

The QC1 analysis scripts triggered after the pipeline processing generate QC reports (graphical information) and measure some additional parameters of lower priority. The measurement of most of these additional parameters might be discarded after some initial time of operations.

QC1 parameters

parameter QC1 database: table, name procedure
qc_post vircam_dark,
qc_post_man, qc_post_mdm
- evaluation of the histogram (distribution) of the master dark. qc_post_man is the histogram center and qc_post_mdm is the histogram width. The parameters are obtained by fitting a Gaussian to the distribution.
pixel property maps vircam_dark, qc_num_hp, qc_num_cp, qc_num_dp, qc_dev_mean, qc_dev_std

- use the qc_post_man and the qc_post_mdm parameters. All pixel with counts more than qc_post_man + 6 * qc_post_mdm are called hot pixel. All pixel with counts less than qc_post_man - 4 * qc_post_mdm are called cold pixel. Calculate the stdev of the counts from each raw input frame and calculate the histogram of all stdev.The two parameters that describe the histogram of all stdev is given in qc_dev_mean and qc_dev_std. Each pixel that deviates more than 6 times qc_dev_std from qc_dev_mean is called a deviant pixel. The number of hot pixel, cold pixel and deviant pixel is given.

short term variations vircam_dark, qc_RON12, qc_RON23, qc_RON34, qc_RON45 - subtract two consecutive DARK raw frames and retrieve a robust estimate of the statistical noise (read out noise) via a histogram fit.

 
 
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