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The VLT instruments pipelines development, integration and maintenance are tasks under the responsibility of the Data Flow System (DFS) group at ESO.
Seven operational instrument pipelines (ISAAC, FORS1, FORS2, NACO, UVES, FLAMES, VINCI) are currently under maintenance, and seven others are being developed and are due over the next two years (CRIRES, VISIR, SINFONI, VIMOS, GIRAFFE, AMBER, MIDI). On top of that, the second generation instruments pipelines will have to be developed from 2005 on at a rate of one pipeline every two years.
The different pipeline tasks are achieved by a number of different software components that can be classified in two distinct categories: those that are common to all instruments and those which are specific to each instrument pipeline package.
The instrument independent components are mainly responsible for the data flow handling.
Each pipeline package contains three software components.
Of course, the instrument specific components have to be developed for each different pipeline, and it is clear that our efforts are put on the reduction of the instrument dependent software size.
The Common Pipeline Library (CPL) (Banse et al. 2004) is a C library that contains all these common functionalities. It has been developed during the last 2 years, and the first public release will take place in December 2003. It is one additional Instrument Independent Component that will reduce the size of the different DRS delivered with the various pipelines packages.
CPL was developed using the C library used for the ISAAC and NACO pipelines: eclipse (Devillard 2001) and the C code developed by ESO for the VIMOS pipeline integration. Particular effort has been put on the documentation and on API clarity, as external consortia will have to base their pipeline development on this library. From now on, every new instrument pipeline will have to be based on CPL. Besides that, the already existing pipelines written in C (ISAAC, NACO, VIMOS, etc..) will have to be converted to use CPL.
The current content of CPL approximately reflects the needs of the pipelines developed so far.
The VLT instruments are each very specific, and their data reduction requirements vary greatly. The following is a short description of the different data reduction modes that can be identified, with their associated instruments.
The high background in infrared data must be carefully estimated to retrieve the science information. In imaging mode, the observations are done in jitter mode, with small offsets around a central position for each exposure, to allow to estimate the sky background variations directly by filtering the images, and separate astronomical from sky signal. Apart from this difficult sky estimation, the frames are recombined with some cross correlation techniques to precisely determine the offsets between the images.
Like for the imaging mode, the high background is removed using special observation techniques. In long slit spectroscopy, shifts are applied along the slit ( nodding) or a tip/tilt is applied to the secondary mirror ( chopping). The pipeline must classify and recombine the frames, and then apply various calibration corrections like, e.g. wavelength calibration, distortion estimation and correction, flat fielding, etc.. The brightest spectrum is then automatically detected and extracted.
The UVES science data contain tilted spectra with the different orders in the same image. To extract all these tilted spectra, a precise spectral format definition (spectra position and wavelength calibration) is needed for all of them. This format is determined by different calibration recipes using lamp images and physical model solutions.
In FLAMES, a series of fibers illuminate the slit. They all generate a spectrum similar to the common UVES observation. These are all stored together in one common image. This requires an even more precise spectral format definition to extract each fiber than for UVES. The reduction for each fiber is then the same as the standard one applied for UVES.
The data produced by Multi Object Spectrograph (MOS) contain a huge number of spectra (up to 800 in VIMOS science images). They all must be identified and wavelength calibrated. The source spectra are then individually sky subtracted, flat fielded and integrated.
In the case of VLTI instruments, the data compression rate is very high. In the case of MIDI, a 2 gigabytes data set is used to obtain a single measurement of the fringes visibility. This means that around 10 measurements can be obtained from a night of observations. The production of a reliable error estimation on the fringes visibility measurements is a very important task of the pipeline.
The Integral Field Unit (IFU) mode is using fiber bundles or an image slicer to observe different parts of extended objects. The different fibers' observations are contained in the same science data, and a very precise calibration (like for the Fiber mode) is needed to extract the correct signals.
The different recipes of the different instrument pipelines produce some quality control (QC) parameters (Hanuschik et al. 2003) that are automatically written in a central log file and a common database. The health of the instruments is then automatically monitored with e.g. the zero point values, the dark current, the strehl ratio, etc..
Banse K. et al. 2004, this volume, 392
Devillard N. 2001, in ASP Conf. Ser., Vol. 238, Astronomical Data Analysis Software and Systems X, ed. F. R. Harnden, Jr., Francis A. Primini, & Harry E. Payne (San Francisco: ASP), 525
Hanuschik R., Hummel W., Sartoretti P., Silva D. 2003, Quality Control of the ESO-VLT instruments, Observatory Operations to Optimize Scientific Return III. Edited by Quinn, Peter J. Proceedings of the SPIE, Volume 4844, pp. 139-148 (2003)