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Quality Control and
Data Processing

CAL | HC | refs | QC
Trending & QC1
QC links:
GRAVITY: P2VM calibrations
QC1 database (advanced users): browse | plot

Measurements for the pixel-to-visibility-matrix (P2VM) are recorded during daytime with the calibration unit, with one of the grisms inserted (low, medium, or high resolution), and with the Wollaston prism either inserted (split) or not inserted (combined polarimetry). A measurement sequence for one set up consists of six exposures where each exposure has two inputs (i.e. one baseline) opened.

P2VM frame. Medium resolution, combined polarimetry, baseline 1-2.

P2VM quality parameters


FITS key QC1 database: table, name definition class* HC_plot** more docu
QC.P2VM_COHERENCE_FT12 gravity_p2vm..coherence_ft12 FT coherence from baseline tel1-tel2 CAL [docuSys coming]
QC.P2VM_COHERENCE_SC12 gravity_p2vm..coherence_sc12 SC coherence from baseline tel1-tel2 CAL [docuSys coming]
QC.P2VM_MINCOHERENCE_FT12 gravity_p2vm..mincoher_ft12 FT minimumcoherence from baseline tel1-tel2CAL [docuSys coming]
QC.P2VM_MINCOHERENCE_SC12 gravity_p2vm..mincoher_sc12 SC minimum coherence from baseline tel1-tel2 CAL [docuSys coming]
QC.P2VM_COHERENCE_AVG_FT gravity_p2vm..coherence_avg_ft mean coherence of P2VM for FT dataCAL [docuSys coming]
QC.P2VM_COHERENCE_AVG_SC gravity_p2vm..coherence_avg_sc mean coherence of P2VM for SC dataCAL [docuSys coming]
QC.P2VM_PHASERMS_AVG_FT gravity_p2vm..phaserms_ft mean RMS of phases of P2VM for FT data CAL [docuSys coming]
QC.P2VM_PHASERMS_AVG_SC gravity_p2vm..phaserms_sc mean RMS of phases of P2VM for SC data CAL [docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one.

Same for baselines 13, 14, 23, 24, and 34.


The QC1 parameters are trended for FT and SC and for the six combinations of resolution and polarimetry mode.

Scoring&thresholds P2VM quality parameters

The normalized coherence should be close to 1 for a good P2VM calibration. In April 2019, scoring thresholds have been revised. As upper threshold, the upper envelope of historical data has been chosen, obvious outliers excluded. Lower thresholds have been set to median - 3sigma, again after excluding strongly deviating data points. Before April 2019, thresholds have been 1.0 and 0.85, respectively.

The thresholds for the phase RMS have been set to median +/- 0.002 in May 2019 which is about +/- 3sigma.


Date event
2016-12 saturated exposures led to some P2VM measurements with poor coherence

Algorithm P2VM quality parameters

Pipeline recipe.

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