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Quality Control and
Data Processing

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   ECH - Grating Position
Solar&sky spectra
QC links:
UVES: ECH Grating Position
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This tutorial provides information for the Echelle grating position.

It is based on the measurement of QC1 parameters of FORMAT CHECK calibration data.
These are obtained with dedicated Health Check OBs executed daily. These OBs obtain four sets of FORMAT CHECK data, 2 sets in BLUE mode and 2 sets in RED mode, each set comprising a single RAW frame. Each set is acquired in a different wavelength setting covering the two arms and the four cross dispersers.

Grating Position (FMTCHK) parameters


FITS key QC1 database: table, name definition class* HC_plot** more docu
QC.MODEL.DIFFXAVG uves_fmtchk..mean_dx difference of X positions to physical modelHC [docuSys coming]
QC.MODEL.DIFFYAVG uves_fmtchk..mean_dy difference of Y positions to physical modelHC [docuSys coming]
QC.MODEL.NLINSEL uves_fmtchk..nlin_sel number of lines selected HC [docuSys coming]
INS.TEMP1.MEAN uves_fmtchk..ins_temp1_mean average temperature of camera [C] HC [docuSys coming]
QC.ORDMIN uves_fmtchk..order_min minimum order number CAL [docuSys coming]
QC.ORDMAX uves_fmtchk..order_max maximum order number CAL [docuSys coming]
QC.MODEL.DIFFXRMS uves_fmtchk..sigma_dx rms of difference of X positions to physical model CAL [docuSys coming]
QC.MODEL.DIFFYRMS uves_fmtchk..sigma_dy rms of difference of Y positions to physical model CAL [docuSys coming]
QC.WLENMIN uves_fmtchk..lambda_min minimum wavelength [Angstrom] CAL [docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one.


Montage of the different QC reports

The montage displays:

  • plot 1:trace across the central row of the RAW frame
  • plot 2:trace across the central column of the RAW frame
  • plot 3:XDIFF vs YDIFF plot, where XDIFF & YDIFF are the differences measured positions of each line with respect to the positions expected from the physical model. Ideally the points in this plot should clusted about 0,0, but the pipeline seems capable to cope with deviations of upto -10,+10 in both axes (the pipeline developer expects 'problems' at values much larger than +/-10 however this range has not been 'explored' in normal operations). Jumps (of completely unpredicatable nature) are often seem in these parameters due to earthquakes and any other influence (e.g. maintenance/intervention operations) which 'disturb' the instrument. Jumps in BLUE and RED arms can be completely UNCORRELATED.
  • plot 4:Distribution of located lines by echelle order
  • plot 5:XDIFFs (as above) as a function of position along each order
  • plot 6:YDIFFs (as above) as a function of position along each order
  • Right, top 1: full display of raw frame
  • Right, lower 1: closeup display of master frame

    There is also a compensation for the thermal drift (X and Y) which has been introduced. This is visible under the Thermal plots.

    Scoring&thresholds Grating Position (FMTCHK) parameters

    Scoring thresholds have been set as an offset around the median.


    The trending of the FMTCHK during the life time of the instrument is best be seen with the full history FMTCHK trending plots shown here: FULL FMTCHK history.

    Algorithm Grating Position (FMTCHK) parameters

  • mean_dx, mean_dy, sigma_dx, sigma_dy: The physical model used in Formatcheck step allows to measure the difference between model predicted and detected line positions. This is useful to verify precision of physical model prediction and instrument spectral format stability. the parameters mean_dx/y represent the difference of X/Y positions to physical model, the sigma : the rms of difference to the physical model
  • median_shftx, median_shfty: median of difference in X to reference frame (stability check)
  • nlin_all: The physical model used in the Formatcheck step allows to predict line positions on the formatcheck frame. This is the total number of predicted matching lines.
  • nlin_sel: The physical model used in the Formatcheck step allows to predict line positions on the formatcheck frame. The selected number of lines is the subset of the total number of lines which fall in the physical model plot limits.

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