ABSTRACT The VLTI Data Flow Operations consist in monitoring the performance of the different VLTI instruments offered to the community, in verifying the quality of the calibration and scientific data and their associated products. Since the beginning of MIDI (April 2004)  and AMBER (October 2005) Service Mode Operations, scientific as well as calibration data have been accumulated to monitor the instruments and the quality of the observations on different time scales and under different conditions or system configurations. In this presentation, we will describe the Quality Control procedures and give some statistics and results on the different parameters used for instrument monitoring for time scales from hours to years in the case of MIDI. We will show that this includes parameters extracted directly from the instruments (Instrumental Transfer Function, Flux stability, Image Quality, Detector stability …) and parameters extracted from some of the sub-systems associated to the instruments (Adaptive Optics, telescopes used …). We will discuss the development of the monitoring of the instruments once more instrument modes or sub-systems such as PRIMA are offered to the community

I Percheron

Sabine Moehler

CiteSeerX

 
 
 
 
Quality Control and Instruments Monitoring for the VLTI 
I. Percherona,*, Sabine Moehlera  
European Southern Observatory (ESO), Karl-Schwarzschildstr. 2, D-85748 Garching bei München, 
Germany  
ABSTRACT 
The VLTI Data Flow Operations consist in monitoring the performance of the different VLTI instruments offered to the 
community, in verifying the quality of the calibration and scientific data and their associated products. Since the 
beginning of MIDI (April 2004) and AMBER (October 2005) Service Mode Operations, scientific as well as calibration 
data have been accumulated to monitor the instruments and the quality of the observations on different time scales and 
under different conditions or system configurations. In this presentation, we will describe the Quality Control procedures 
and give some statistics and results on the different parameters used for instrument monitoring for time scales from hours 
to years in the case of MIDI. We will show that this includes parameters extracted directly from the instruments 
(Instrumental Transfer Function, Flux stability, Image Quality, Detector stability …) and parameters extracted from 
some of the sub-systems associated to the instruments (Adaptive Optics, telescopes used …).  We will discuss the 
development of the monitoring of the instruments once more instrument modes or sub-systems such as PRIMA are 
offered to the community. 
Keywords: VLTI, Interferometry, instrument monitoring, quality control, instrument trending 
 
THE VLTI INSTRUMENTS 
The VLT Interferometer (VLTI) has been operating on Paranal since 2001 with first fringes obtained at 2μm with 
VINCI, the VLTI commissioning instrument. Since Period 73 (April 2004), MIDI (the MID-infrared Instrument for the 
VLTI), operating in the N Band between 8 to 12  μm is offered for Service Mode Observations (SM). For the past period 
(October 2005 to April 2006), MIDI was offered using the UT (Unit Telescopes 8.2m) or the AT (Auxiliary Telescopes: 
1.8m). The second VLTI instrument AMBER (near-infrared/red focal instrument for the VLTI), operates in the bands J, 
H and K and has been offered for SM operations since P76 (October 2005 with either 2 telescopes or 3 telescopes. The 
instruments are described in ref. 4 and 5, while the operations are described in ref. 1 and ref. 3. Both instruments are part 
of the Data Flow and Quality Control Operations (DFO and QC) in Garching. 
DATA FLOW AND QUALITY CONTROL OPERATIONS 
 
 
 
Fig 1: The observed data are archived on Paranal and are shipped to Garching several times a week. The VLTI data 
(typically 15GB a night for MIDI SM night and 5 GB for AMBER SM Night) are retrieved on the dedicated DFO 
machines for processing, quality control, instrument trending, health check and packing.  
*ipercher@eso.org 
 
Post-processing 
 
Processing and QC 
checks of the 
Calibration files 
 
Pre-Processing 
 
Download of the data 
Association of the calibration  
Raw data for processing 
Quality Control checks and 
certification of the calibration files 
Processing and QC 
checks of the Science 
files 
Association of the science  
raw data with certified calibration 
products for processing 
Quality Control checks and 
certification of the science files 
Reports 
Service Mode data 
packages  
(distributed to the PI by 
the ESO archive) 
Certified Calibration Products 
Science Products 
 
 
 
 
The quality of all data measured with the VLT and VLTI during Service Mode operations are evaluated by the QC group 
in Garching. This is done using data flow operations and is illustrated in Fig 1. 
 
DATA PROCESSING AND QUALITY CONTROL FOR VLTI. 
1.1 Data association, pipeline processing and data products 
 
All the raw data are processed using the ESO pipelines which are integrated in the ESO Data Flow System (DFS). These 
pipelines are running in Paranal and in Garching. In Paranal they are used by the Science Operations team (PSO) to 
assess the quality of the data after the observations and in Garching by the dedicated QC scientist to produce the 
calibrations and the science products. The MIDI pipeline is based on algorithms provided by the consortium; the new 
modes are implemented by ESO. A second MIDI Data Reduction Package, fully interactive has been developed by the 
consortium (ref 2). The AMBER pipeline is still under development in collaboration with the consortium.  
As shown in Table 1, the MIDI mode HIGH_SENS (high sensitivity, the full flux is used to record the fringes, then the 
target and the sky are measured for each beam to calibrate the fringe data), is fully supported for the UTs. With the ATs, 
the mode was not fully supported until end of January 2001. Since then, some hardware and software modifications were 
done and observations on the ATs and the UTs are now processed using the same algorithms. The second MIDI mode 
offered for P76 is the SCI_PHOT mode. In this mode the detector records at the same time the two interferometric 
channels and the two photometric channels. This mode is less sensitive than the HIGH_SENS mode (the light is split 
between the interferometric channels and the photometric channels) but is more accurate (the photometry is recorded at 
the same time than the fringes are acquired). There are 3 main steps for the processing of the data: the estimation of the 
Kappa Matrix, which represents the splitting ratio between the interferometric channels and the photometric channels, 
the estimation of the uncalibrated fringes, the calibration of the fringes with the kappa matrix and the flux. Currently 
only the first two steps are supported by the pipeline, the uncalibrated fringes are used to assess the quality of the 
observation. 
Before processing, the files are associated using specific tools, the Data Organiser (DO) in Paranal and the ABbuilder in 
Garching (AB: Association Blocks). This association is done using specific keywords logged in the raw fits files. In 
Paranal and in Garching, the operations are done night by night, with use of calibrations which could be taken several 
nights/weeks apart. The calibrations products are first created, their quality is assessed and the products are then 
certified. The science data files are associated to calibrations files. The table 1 shows which data are associated before 
the processing. 
 
 Mode category Associated raw files Associated products needed for processing (fits files or tables) 
Pipeline generated 
products 
MIDI HIGH_SENS CALIB 
Interferometry 
photometry 
Calibrator database 
Wavelength table 
Fringe visibility 
TransferFunction 
MIDI HIGH_SENS SCIENCE 
Interferometry  
photometry 
Wavelength table 
Transfer Function  
Fringe visibility 
 
MIDI SCI_PHOT CALIB Photometry files Wavelength table Kappa Matrix 
MIDI SCI_PHOT CALIB Fringe files 
Wavelength table 
Calibrator database 
Kappa Matrix 
Fringe visibility 
TransferFunction 
MIDI SCI_PHOT SCIENCE Fringe files 
Wavelength table 
Transfer Function 
Fringe visibility 
 
 
Table 1: Each observation represents several fits raw files which are associated and classified following rules. Each set of 
associated raw file will produced one or several products. 
When the files are associated, they are classified and sent to the pipeline for data analysis and to create the products. In 
the case of VLTI, the pipeline is still under development and the pipeline products are distributed to the community (PI) 
but cannot be used directly for high accuracy analysis. The table 2 describes the ESO pipeline products and the main 
Quality Control Operations for each instrument mode.   
 
 
 
 
 
 
Table 2: The processing of the set of associated fits files produce one or several products (fits files or table). These files 
contain the results (following the OIFITS format for the fits files), and different QC parameters which are used for 
Quality Control, instrument trending and health check. 
Technical Calibrations 
Unlike the other VLT instruments, the VLTI instruments do not require the typical day time calibrations. Both MIDI and 
AMBER follow a calibration plan which include for MIDI data taken to measure the detector linearity, the detector 
Read-Out-Noise, the transmission of the dispersive elements, and the position of the reference pixels. Reference frames 
are also compiled and used by the Paranal operator when starting the instrument (see fig. 2). Data are also taken for 
wavelength calibration.  More information can be found at http://www.eso.org/observing/dfo/quality/MIDI/qc/qc1.html 
 
 Instrument Mode Category 
Resolution 
element 
Instrument 
setup 
ESO Pipeline 
products 
Main QC parameters or 
plots 
CALIB 
-Size of the acquisition image, 
-Quality of the photometry 
-Dispersed visibilities 
-Instrumental Transfer Function HIGH_SENS 
(+acquisition) 
SCIENCE 
PRISM or 
GRISM 
AT 
- Acquisition product 
- No reduced fringe for 
P76 
(Supported for P77) 
 
-Size of the acquisition 
image, 
-Quality of the photometry 
-Dispersed visibilities 
-Calibrated Visibilities 
CALIB 
-Size of the acquisition 
image, 
-Quality of the photometry 
-Dispersed visibilities 
-Instrumental Transfer Function HIGH_SENS 
(+acquisition) 
SCIENCE 
PRISM or 
GRISM 
UT 
-Acquisition product 
-reduced fringe product 
 
-Size of the acquisition 
image, 
-Quality of the photometry 
-Dispersed visibilities 
--Calibrated Visibilities 
CALIB 
-Acquisition product 
-Kappa Matrix 
-reduced uncalibrated 
fringe product 
-Size of the acquisition 
image, 
-Quality of the photometry for 
the kappa Matrix 
-Kappa Matrix 
MIDI 
SCI_PHOT 
(+acquisition) 
SCIENCE 
PRISM or 
GRISM 
UT 
-Acquisition product -Size of the acquisition 
image 
Low 
JHK or HK 
2 or 3 beams 
Medium 
JH or HK or 
K 
2 or 3 beams 
AMBER 
Standard or 
differential 
phase 
CALIB or 
SCIENCE 
High 
J or H or K 
2 or 3 beams 
-Pixel to Visibility 
Matrix (P2VM), 
-Fringe product (1 per 
band per baseline) 
-P2VM offset, 
-Piston, SNR, dispersed 
Visibilities, Averaged Visibility, 
Flux, 
-Phase Closure for 3 beams 
 
 
 
 
 
 
Fig. 2: Example of MIDI calibrations: transmission of the PRISM and MIDI reference frame. Note that for the transmission 
of the PRISM plot, the data > 1 shows that there was some saturation in the image which was not taken into account by 
the pipeline recipe. This is under investigation. 
 
For AMBER, data are taken to calculate the Bad Pixels Map (BPM) and the Flat Field Map (FFM). Since the end of P76, 
MIDI calibration data are taken at least once a month. These data are processed with the pipeline and the analysis and the 
monitoring of the results are part of the health check and the monitoring of the instrument. For AMBER, the technical 
calibration data have been taken once and the BPM and FFM have been generated by the consortium and are distributed 
with the SM data packages as well as with the data analysis package developed by the consortium. 
 
Fig. 3: BPM and FFM for the AMBER instrument. 
Astronomical Calibrators data 
As with the other ground based interferometers, the VLTI is affected by the atmospheric turbulence. To calibrate the 
science data, one is required to measure the instrumental Transfer Function using an astronomical calibrator with a well 
known diameter or an unresolved source (see ref 6). A VLTI observation associates always an astronomical calibrator 
and a science target. The selection of the calibrator can be done using several approaches. The calibrator can be chosen 
in catalogs using selection criteria (non variable, non multiple, no infrared excess or peculiar spectrum …), the second 
approach (which is chosen by the VLTI) is to compile list of potential calibrators either from existing measurements or 
 
 
 
 
with estimated diameters. The second option allows a monitoring of the calibrators and the fig. 4 shows the sky coverage 
for MIDI and AMBER as well as the sky coverage of the VINCI calibrators.  
At the preparation of the SM observations, the PI can choose a calibrator from the VLTI calibrator Database (CalVin 
available at http://www.eso.org/observing/etc/) or select his own astronomical calibrator if none are available from 
CalVin. If the calibrator is chosen from the VLTI database, and if the mode is fully supported by the pipeline, the 
associated Transfer Function is calculated by the pipeline and is used to calibrate the Science data if any is associated 
and for instrument trending (see section 1.2).  
 
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
0 4 8 12 16 20 24
RA
D
E
C
AMBER
MIDI
VINCI
 
 
Fig 4: Sky coverage for the MIDI, AMBER and VINCI calibrators. The MIDI calibrators have been provided by the 
consortium while the AMBER calibrators list has been compiled from existing catalogs (see ref 8) 
Science Products 
Each science target is processed by the pipeline. If a transfer function (TF) is measured close (in time) to the science 
object, the visibility measured on the calibrator is calibrated with the TF and a calibrated visibility is also distributed with 
the product. If there is no calibrator from CalVin observed close in time to the scientific target, only the uncalibrated 
visibility is present in the product. The products are checked for quality and distributed to the PI. Because of the possible 
complexity of the object, the product is checked only for obvious problems. 
 
1.2 Quality Control and Instrument trending 
MIDI 
For the HIGH-SENS mode, the quality of the visibility obtained is directly related to the accuracy of the measurement of 
the flux of the object taken after the observation of the fringe. The QC procedures check the quality of the photometric 
data. The figure 5 shows 2 sets of photometric data, one with some chopping problems (top), another one of good quality 
data (middle). 
In the case of a calibrator, the flux on the target should be easily measured; the calibration product is not certified if this 
is not the case. In the case of a science target, the stability of the photometry is used.  
 
 
 
 
The second step in the certification of the calibration product is the value of the TF (if available) or if no TF is available, 
the shape and the value of the calibrator visibility. Even if the diameter of the calibrator is unknown because not chosen 
in the CalVin database, the calibrator should be small (point source like) and without spectral feature or infrared excess. 
Its visibility across the spectrum should be without features and its height closed to the expected TF (fig 4, bottom).  The 
visibility of the Science object is also studied but is not taken into account. 
 
 
 
Fig 5: Quality control on the photometric data (top and middle) and on the dispersed Visibility vs. wavelength. For the top 
and middle images the X axis represents the frame number (1 to 8000 for the top image, 1 to 1500 for the middle), the 
Y axis the flux. In the top image, the flux of the target (crosses) shows variations. 
The instrument monitoring consists mainly in following the variation of the TF on different time scale: during the night 
or for a full observing Period (6 months). An example is shown in the figure below.  
 
 
Fig 6: Transfer Function for the MIDI instrument 
AMBER 
The AMBER instrument is described during this conference (ref 3). AMBER quality control consists mainly in 
monitoring the offset between the different photometric and interferometric channels (fig. 7). This offset is calculated 
during the calibration of the Pixel to Visibility Map (P2VM). 
 
 
 
 
 
 
 
Fig 7: offsets for the photometric channels as calculated by the pipeline. For good quality data, this offset should not be 
larger than 3. The scale represented here is -1, +5. 
 
Different plots are also produced using the data products; a final plot containing them is generated and included in the PI 
packages (fig. 8). 
 
Fig 8: Quality Control plot produced for AMBER using 3 telescopes (3 baselines). The data on the left show respectively 
(top to bottom) the Visibility vs the fringe SNR, the Visibility vs the fringe piston and the piston vs the fringe SNR. 
The Visibility plots are scaled between -0.2 and 1.2. The middle top plots show also the Visibility vs SNR and vs 
Piston but with the real scale and show the outliers. The middle plot shows the piston vs time. 
 
 
 
 
VLTI 
The VLTI is not limited only to the interferometric instruments MIDI and AMBER but includes also a variety of 
subsystems such as MACAO (the adaptive optics system for the VLTI at the UTs), the delay lines, the variable curvature 
mirrors (VCM). Some of them need to be controlled and monitored. During this conference, a poster (ref 9) is presented 
on the influence of the MACAO performances on the interferometric measurements. During the campaign of observation 
with MIDI on the AT, the importance of the VCMs was also shown.   
 
QC AND THE INTERFEROMETRIC COMMUNITY 
 
The main interaction between the QC group in Garching and the astronomical community is the compilation of the PI 
data packages. During P76, more than 80 packages were sent to the different AMBER and MIDI PIs. 
 The study of the potential VLTI calibrators is also an important part of the Quality Control tasks done in collaboration 
with the interferometric community.  A calibrator program was started at ESO at the beginning of the VINCI 
observations (ref 7). The same program is also under way with MIDI and AMBER. The observations on the calibrators 
are analyzed and the results are used to update the list of potential calibrators used in CalVin (for example variable 
objects or calibrators with infrared excess are removed). 
REFERENCES 
1. S. Morel et al., “Preparing MIDI science operation at VLTI”, New Frontiers in Stellar Interferometry, SPIE, 1666 
(2004). 
2. C. Hummel, I. Percheron., “Pipeline reductions of VLTI/MIDI data and quality control”, Advances in Stellar 
Interferometry, SPIE, this volume (2006). 
3. F. Rantakyro et al., “Experiences from the first AMBER open time observations”, Advances in Stellar 
Interferometry, SPIE, this volume (2006). 
4. C. Leinert et al., “Ten-micron instrument MIDI: getting ready for observations on the VLTI”, Interferometry for 
Optical Astronomy II, SPIE, 893-904 (2003). 
5. R. Petrov et al., “Using the near infrared VLTI instrument AMBER”, Interferometry for Optical Astronomy II, SPIE, 
924-933 (2003). 
6. A. Richichi, I. Percheron, M. Khristoforova, “CHARM2: An updated Catalog of High Angular Resolution 
Measurements”,  A&A 431, 773 (2005).  
7. A. Richichi, I. Percheron, “First results from the ESO VLTI calibrators program”,  A&A 434, 1201 (2005).  
8. Merand A. et al., “A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry”, A&A 
447, 783 (2006). 
9. I. Percheron et al., “Adaptive optics quality metrics and user constraints set for the VLTI”, Advances in Stellar 
Interferometry, SPIE, this volume (2006). 
 


Quality control and instruments monitoring for

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=4789B97E1E3B8F6E26D3AE297F423F18?doi=10.1.1.1068.6383&rep=rep1&type=pdf

Quality control and instruments monitoring for

Abstract

Similar works

Full text

Available Versions

CiteSeerX