Quality Control: twilight flats

VIRCAM Quality Control:
Twilight Flats

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noise parameters | flat flux level | sequence


QC PLOTS
	CURRENT	HISTORY
master noise and struct.
raw twil counts average
raw twil counts range
master S/N
rms of flat ratio
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.

Each detector has its own response. Therefore twilight flats show the following relative ADUs:

chip13	chip 14	chip 15	chip 16
0.79	1.04	1.17	0.91
chip 9	chip 10	chip 11	chip 12
1.04	1.13	1.03	1.13
chip 5	chip 6	chip 7	chip 8
1.08	1.19	1.26	1.01
chip 1	chip 2	chip 3	chip 4
1.24	0.79	0.86	1.04

chip #1 and #13 showing the smallest response and chip #1 and #7 showing the largest response.

top noise parameters

QC1 parameters

parameter	QC1 database: table, name	procedure
twilight flat rms	vircam_twil, qc_twil_rms	- The QC.FLATRMS is a measure of RMS in ADU obtained from master twilight flat products. It is the median of the absolute deviations from the median ( = MAD ) times 1.48 derived from the master twilight flat.

top twil level

QC1 parameters

parameter	QC1 database: table, name	procedure
qc_twflat_medavg	vircam_twil, qc_twflat_medavg	- The average of the raw flat medians. Derived from QC in Garching. Not derived by pipeline. There are further parameters obtained from the raw frame median values.
RMS of ratio flats	vircam_twil, qc_ratiotwil_med, qc_ratiotwil_rms	- For the QC.FLATRATIO_MED parameter, the master twilight flat is divided by a reference twilight flat product ( PRO.CATG = REFERENCE_TWILIGHT_FLAT ). The median and the robust noise, using MAD, of the ratio frame is given

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 or included in the vircam pipeline.

QC1 parameters

parameter	QC1 database: table, name	procedure
sequence property	vircam_twil, qc_twflat_medmin, qc_twflat_medmax, qc_twflat_medavg, qc_twflat_medstd, qc_twflat_medrng	- The fluxes of the twilight flat raw frames vary as the sky brightness varies during dusk or dawn. For each raw frame the median counts is taken. Out of this sample of raw frame medians the minimum, the maximum, the average, the standard deviation and the range is extracted.
	vircam_twil, qc_photnoise, qc_phot_sn, qc_diff_avg, qc_diff_std	- subtract two consecutive raw twilight flat frames (align them by flux) and retrieve a robust estimate of the statistical noise (read out noise) via a histogram fit. qc_diff_avg and qc_diff_std are the Gauss fit parameters when fitting the histogram of the flux-aligned raw twilight flat difference frame. qc_photnoise is the photon noise and qc_phot_sn is the signal to noise ratio.
pre reset-corrected maximum flux in saturation level units	vircam_twil, qc_twflat_fracsat	- Among all median flux values obtained from the raw fats, the highest flux value is multiplied by (MINDIT+DIT) / DIT to get the flux value on the chip before the detector reset was subtrcated by the acquisition system. The value is compared with the saturation level. Details are given on the problems page.