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Project DR-02

Stacking and mosaicing of dithered / jittered images

As for the task DR-01, the purpose of this project is to provide a set of pipeline recipes based on the ESO Common Pipeline Library (CPL) for the stacking and mosaicing of imaging data. Currently a lot of observers split observations of a given target among different OBs. A set of CPL recipes will provide a seamless interface to the existing pipelines and to the execution front-end tools esorex, Gasgano and ESO Reflex.

The task DR-02 deals with the correction of the data by the photometry and astrometry solution defined in DR-01. The task DR-02 performs the image combination into a mosaic, and copes with:

  1. overlaps,
  2. global fringing correction,
  3. background matching,
  4. variable seeing,
  5. rejection of data based on seeing, image quality, or signal-to-noise criteria,
  6. propagation of errors

A well-known technique to reduce the influence of thermal and background noise in ground-based infrared imaging is chopping and nodding. In it simplest form, this results in four different signals (two on-source and two off-source) which are subtracted from one another pair-wise and then combined to a net image. Since noise in the data can severely affect the reconstruction, regularization algorithms have to be implemented. In particular, when performing raster maps, observing crowded or extended regions (Orion, M17, GC, etc.) dedicated inversion problems have to be solved but are not currently implemented in the VLT pipelines. Proposed solutions to this problem are given in the following references.


  • Vandame, B., 2003, New algorithms and technologies for the un-supervised reduction of Optical/IR images, astroph:0208230v1
  • Astro-Wise project: http://www.astro-wise.org, http://www.astrometry.net
  • Anconelli et al., 2006, A&A, 460, 349
  • Bertero et al., 2000, PASP, 112, 1121
  • Lenzen et al., 2005, A&A, 443, 1087


Applicable instruments and modes

This project is applicable to all ESO imaging instruments in optical and near-infrared (e.g. FORS, ISAAC, SOFI, VIMOS, WFI, etc..). This also applies to thermal instrumentation in N,Q bands (VLT:VISIR, ELT:MIDIR) and L,M bands (VLT: NACO, ISAAC,etc.)

Required archive, calibration or observation data

A lot of observers split observations of a given target among different OBs. Data required for this project is available in the ESO archive.

Required algorithm and software developments

The development is divided into two tasks: DR-01 is concerned with the determination of the photometry and astrometry solution to a set of data, while DR-02 is the task of combining these data into a mosaic. The task DR-02 involves the following steps:

  1. Evaluate the existing MVM and Terapix (scamp, swarp) packages both in terms of functionality, performance, and software structure (http://archive.eso.org/cms/eso-data/data-packages/eso-mvm-software-package, and http://terapix.iap.fr/).
  2. Define a rejection method that can take into account criteria of seeing, image quality, and signal-to-noise in the data (currently not supported by MVM). One can assume that the image quality has been measured by a previous recipe.
  3. Allow the user to provide a pre-calculated distortion map (currently not supported by MVM).
  4. Allow the user to check the astrometric and photometric corrections on the overlaps and, if necessary, adjust the correction to match the overlap regions.
  5. Resample the data into a common astrometric grid.
  6. Apply photometry correction, taking into account background matching, overlaps, global fringing
  7. Deliver the mosaiced image with error estimates.


Required software developments

All software will be developed following the guidelines of the VLT-SPE-ESO-19000-1618 document. The software delivery will include in particular the CPL-based recipes, test reports, user documentation and Reflex workflows. A prototype based upon available software products shall be first developed and reviewed as additional part of the detailed specifications.


The result of the combination will be compared to results obtained by the standard MVM package (http://archive.eso.org/cms/eso-data/data-packages/eso-mvm-software-package) for a set of selected data sets (FORS, VIMOS, WFI, VISTA, HAWK-I, ISAAC, NACO, VISIR). ESO will process the raw data for the selected data sets and provide the corresponding pipeline products. A suitable test field will be the CHANDRA Deep Field South, for which both ESO data and published results are available.



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Vienna University
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