Quality Control and
Data Processing

HC PLOTS
RMS of master flat
RMS of ratio flat
counts avg
counts range
QC1 database (advanced users): browse | plot

VIRCAM dome flats are technical calibrations, to monitor flat field cosmetics. Dome flats are acquired by illuminating the screen inside the telescope building with several halogen lamps. They can serve as a substitute for twilight flats in case twilight flats cannot be acquired for a longer times.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.FLATRMS	vircam_dome..qc_dome_rms		ENG		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

Trending

The rms of the master dome flat is monitored for all filters: NB118, NB980, Y, Z, J, H ,K separately. The K-band is monitored here.

Scoring&thresholds RMS of master dome flat

Not scored

History

No remarks.

Algorithm RMS of master dome flat

The QC.DOMERMS is a measure of RMS in ADU obtained from master dome flat products. It is the median of the absolute deviations from the median ( = MAD ) times 1.48 derived from the master dome flat.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.FLATRATIO_RMS	vircam_dome..qc_ratiodome_rms		ENG		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

The vircam dome flat pipeline recipe allows to specify a reference flat, which can be any master dome flat. The pipeline divides the master flat by the submitted reference flat and extracts some QC parameters of which the RMS of the ratio flat is the most important. The pixel-to-pixel relative response differences (= the fixed pattern noise), which dominate the RMS of the master flat, are canceled out in the ratio flat. The RMS of the ratio flat is therefore sensitive to other changes in the master flat, like:

• changes in the relative gain of the 16 read-out channels (16 vertical stripes each one 128 pixel wide). In addition to the qc_ratiodome_rms we monitor qc_dome_chanRMS. wich divides the ratio dome flat in 16 junks (the 16 read-out channels), takes the average signal of each of the 16 detector areas and determines the rms over these 16 channel means. By this QC1 parameter it is possible to disentangle the channel gain contributions from other contributions to the overall qc_ratiodome_rms. This becomes important for the period starting in early 2020 (after a detector controller intervention), when the channel gain variations increased and became the dominating contribution to the qc_ratiodome_rms, in particular for detectors #6 and #10, #12 and #14. In this period the values of qc_ratiodome_rms are dominated by channel gain variations and are no longer sensitive to the detector characteristics originally intended to be monitored, in particular for detectors #6 and #10, #12 and #14.
• new dust grains
• new bad pixel (e.g. 2013-03--01 on chip #3)
• controller issues

Trending

The RMS of the ratio dome flat is monitored here.

Scoring&thresholds RMS of ratio flat

The values are not scored

History

The maintenance of the reference flat means it has to be updated from time to time, typically twice a year and after interventions. The dome flat QC1 DB contains the name of the reference twilight flat (qc_dome_refname) and the time stamp of the reference dome flat (qc_dome_refdate).

Algorithm RMS of ratio flat

The master flat is divided by the reference flat, the RMS is taken.

For reasons of demonstration we have performed the following exercise: We have processed the H-band dome flat from 2022-10-01 using the linearity calibration products CHANNEL_TABLE and BadPixelMap also from 2022-10-01. We have registered this MASTER_DOME_FLAT as REFERENCE_DOME_FLAT for the subsequent analysis. In a first sequence, we have processed some other H-band dome flats of 2022-10 and 2022-11 using the same REFERENCE_DOME_FLAT and the same CHANNEL_TABLE and BadPixelMap from 2022-10-01.

	QC report of MASTER_DOME_FLAT from 2022-10-01. REFERENCE_DOME_FLAT is the MASTER_DOME_FLAT, hence the RATIO_DOME_FLAT is 1.0.
	QC report of MASTER_DOME_FLAT from 2022-11-09. The same CHANNEL_TABLE and the REFERENCE_DOME_FLAT from 2022-10-01 is used. There are no channel gain variation in this particular RATIO_DOME_FLAT, as they are introduced by the same CHANNEL_TABLE product.

In a second sequence we have processed the 2022-10-01 dome flat a second time using the CHANNEL_TABLE from 2022-11-05.

	QC report of MASTER_DOME_FLAT from 2022-10-01 calibrated with the CHANNEL_TABLE from 2022-11-05. The channel gains have changed and become apparent in the RATIO_DOME_FLAT.
	H-band dome flat of chip #12. raw frame.

The channel gain variations of the order of 2\% become visible only in the RATIO_DOME_FLATs where all other spatial large scale illumination are canceld out.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
average counts	vircam_dome..qc_dome_medavg		ENG		[docuSys coming]
range	vircam_dome..qc_dome_medrng		ENG		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

Trending

While twilight flats are affected by the decreasing sky brightness during dawn, dome flats are illuminated by a set of stable lamps. The average counts in dome flats is monitored here . The stability of the lamp within the series of five raw frames is monitored via the counts range parameter.

While the dome flat field lamps, both the ones used for the H and K band as well as those used for the bluer bands Z, Y, J, NB118, NB980, are stable over a longer period, the K-band dome flat counts show a correlation with the ambient temperature (see Fig. below).

Scoring&thresholds Counts in dome flats

The values are not scored.

History

On 2018-08-07, M1 and entrance window was washed. Counts of dome flats (which pass M1 and entrance window) increased from 6500 ADU to 7200 ADU for the Y-band e.g., a value with was registered the least time in late 2011.

Algorithm Counts in dome flats

The counts, the average over five raw frames is taken.

Relation between the average counts in K-band dome flats and the ambient temperature. Data cover the period 2015 - 2023.