Quality Control and
Data Processing

HC PLOTS
Detector linearity
QC1 database (advanced users): browse | plot

The linearity of the ESPRESSO detectors is assessed by a series of exposures using the LED flat-field lamp with increasing exposure time. Exposures come in pairs of equal exposure time and are preceeded by ten bias frames. After bias subtraction, the function

ADU = A + B * EXPTIME + C * EXPTIME^2

is fit to the average level of the flats for each of the 16 read-out ports separately. The coefficients A, B, and C are saved into an output file. They are not used further for data reduction since the ESPRESSO detectors do not show significant non-linearity.

For monitoring, the QC parameter effective non-linearity is used. It is the difference between the flux obtained at the reference level 20000 ADU from the polynomial fit and the flux predicted by the linear term only, normalized by the polynomial flux. The mean level of the flats with the highest exposure time must, therefore, be well above 20000 ADU for a correct calculation of effective non-linearity.

Raw detector monitoring frame. Example frame for the blue detector. The gaps are due to the pre-/overscan of the 16 read-out ports

QC1_parameters

FITS key	QC1 database: table, name	definition	class*	HC_plot**	more docu
none	espresso_detmon..lineff_avg	average non-linearity across read-out ports	HC		[docuSys coming]
none	espresso_detmon..lineff_rms	RMS of non-linearity across read-out ports	HC		[docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter **There might be more than one.

ESPRESSO has two chips, one for the BLUE and one for the RED arm. Each chip has 16 read-out ports. Linearity QC parameters are determined by the pipeline per read-out port which leads to 16 different values for each QC parameter per chip. The parameter names in the QC1 database follow the scheme

lineff_<x>_<y>

with <x> being the x position of the read-out on the chip (0, 1, to 7), and <Y> the y position (0 or 1).

In addition to these individual values, the average and the RMS per chip are calculated and written into the QC1 database.

Trending

Non-linearity is trended separately for the four different read-out modes: 1x1 binning (fast read-out), and 2x1, 4x2, and 8x4 binning (all slow read-out).

Scoring&thresholds Detector linearity

Scoring is not yet implemented.

History

Measurements started in January 2020.

Algorithm Detector linearity

The generic detector monitoring recipe is used.