Quality Control and
Data Processing

HC PLOTS
gain
deviation from linearity
number of non-linear pixels CCDs
linearity min/max
fixed-pattern noise
QC1 database (advanced users): browse | plot

The OmegaCAM linearity/gain template is normally taken every 10 days and consists of 20 dome flat images taken in pairs of 2, 5, 7, 10, 20, 30, 40, 50, 60, and 70 second exposures and two bias frame exposures. The template MUST be executed in the v_STRM filter, since using the Sloan filters would result in the long exposures saturating (e.g. in z_SDSS the dome flat will saturate in 4.0 seconds).

The OmegaCAM gain is derived for the full flux range. By plotting the mean_flux[on_1] + mean_flux[on_2] - (mean_flux[off_1] + mean_flux[off_2]) vs the variance (sigma^2[on] - sigma^2[off]) for each dome flat exposure pair, a linear fit to the data (green line) gives the inverse (1/gain) value.

The pipeline creates seven output frames from an external detector monitoring recipe (detmon_opt_lg): a gain parameter fits table (OC_PDGI_<DATE>_1_1_normal_normal_<FILTER>.fits), a linearity parameter fits table (OC_PDLI_<DATE>_1_1_normal_normal_<FILTER>.fits), an image map of non-linear pixels (OC_PDNL_<DATE>_1_1_normal_normal_<FILTER>.fits), and three further images of the linearity coefficients (OC_PDC0_<DATE>_1_1_normal_normal_<FILTER>.fits, OC_PDC1_<DATE>_1_1_normal_normal_<FILTER>.fits, OC_PDC2_<DATE>_1_1_normal_normal_<FILTER>.fits)

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.GAIN	omegacam_detlin..qc_gain	gain (e-/ADU)	HC		[docuSys coming]
QC.GAIN.ERR	omegacam_detlin..qc_gain_err	error in gain (e-/ADU)	HC		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

Trending

Following parameters are monitored in trending plot.

• the gain averaged over all 32 detectors (e-/ADU)
• the error in the gain averaged over all 32 detectors (e-/ADU)
• the gain for each individual detector (e-/ADU)
• score outliers

Scoring&thresholds GAIN

The gain averaged over all CCDs is scored tightly with +/- 5% thresholds. The averaged gain error is scored with +/- 20% thresholds.

History

Date	event
2012-09-13	The gain is very stable in the long-term for all detectors
2019-01-05	Data taken with M1 cover closed
2020-11-15	CCD77 does not work; only displays random signal consistent with noise (PPRS-079377)
2022-05-09	CCD77 started recording some coherent signal again

Algorithm GAIN

The standard, detector monitoring procedure is applied.

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
QC.LIN.EFF	omegacam_detlin..qc_lin_eff	effective non-linearity correction	HC		[docuSys coming]
QC.LIN.EFF.FLUX	omegacam_detlin..qc_lin_eff_flux	flux level at which effective non-linearity correction is applied	HC		[docuSys coming]
[calcutaed by QC script]	omegacam_detlin..qc_num_bpm	number of (bad) non-linear pixels	HC		[docuSys coming]
QC.COUNTS.MIN	omegacam_detlin..qc_counts_min	minimum median value used in linearity	HC		[docuSys coming]
QC.COUNTS.MAX	omegacam_detlin..qc_counts_max	maximum median value used in linearity	HC		[docuSys coming]
QC.FPN	omegacam_detlin..qc_fpn	fixed pattern noise	HC		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

Trending

Following parameters are monitored in this trending plot:

• effective non-linearity correction averaged over all 32 detectors
• effective non-linearity correction for each individual detector
• flux level at which effective non-linearity correction is applied averaged over all 32 detectors (ADU)
• score outliers

In this trending plot:

• number of non-linear pixels averaged over all 32 detectors
• number of non-linear pixels for each individual detector
• score outliers

In this trending plot:

• minimum/maximum median flux level used in the linearity computation averaged over all 32 detectors (ADU)
• minimum/maximum median flux level used in the linearity computation for each individual detector (ADU)
• score outliers

In this trending plot:

• fixed-pattern noise averaged over all 32 detectors (ADU)
• fixed-pattern noise for each individual detector (ADU)
• score outliers

Scoring&thresholds LINEARITY

The effective non-linearity correction and fixed-pattern noise averaged over all 32 are loosely scored with fixed thresholds.

History

Date	event
2012-09-13	The linearity coefficients are very stable in the long-term for all detectors
2019-01-05	Data taken with M1 cover closed
2020-11-15	CCD77 does not work; only displays random signal consistent with noise (PPRS-079377)
2022-05-09	CCD77 started recording some coherent signal again

Algorithm LINEARITY

The standard, detector monitoring procedure is applied.