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Project DR-04

Mosaicing of spectral-imaging data (3D cubes)


This project addresses mosaicing/stacking of 3D data cubes for VIMOS, SINFONI, and GIRAFFE IFU data. The goal is to review existing available methods, evaluate combination strategies for existing instruments, and provide CPL-based routines.

Note: First priority shall be given to the VLT 1st generation instruments. Depending on the timescale of the project and the availability of test or simulation data, extending the module to 2nd generation VLT Instruments such as MUSE (Multi Unit Spectroscopic Explorer; www.eso.org/instruments/muse/) and KMOS (infrared multi-integral field spectrograph; www.eso.org/instruments/kmos) could be investigated.



Applicable instruments and modes



Required archive, calibration or observation data

Mosaicing data suitable for 3D combination are probably taken commonly with VIMOS, SINFONI, GIRAFFE IFU, and more detailed information could be obtained from the User Support Department. Data for all these 3D instruments can be obtained from the ESO archive.


Required algorithm developments 

Most, if not all 3D spectroscopic measurements will require multiple exposures of the source to build up sufficient signal-to-noise. Two methods often used for such measurements are the alternating source-sky mode (though not necessarily in equal proportions) and the dither, or "shift and stare" mode (in fact, these two modes are often used together). In the former case extremely tight (and often unrealistic) constraints are placed on the system to return to the exact pointing position on each subsequent source exposure, while in using dithering one intentionally displaces the source from one exposure to the next. Moreover, many 3D instruments, in operation or being developed, have small fields-of-view, and to image larger fields requires multiple (overlapping) pointings. All these facts lead to the conclusion that a 3D mosaicing tool is required to analyze 3D spectroscopic data.

Mosaicing of 3D data has been addressed within the Euro3D network. Available methods and their relevance for ESO instrument data should be studied, in order to identify the necessary further developments. A task breakdown for this project would include the following steps:

  1. Retrieve archive data from the above mentioned instruments, obatin pipeline reduced data from the ESO Data Products Department.
  2. Define a product interface (requirements on the pipeline products for this task)
  3. Develop procedures for relative (and absolute) flux scaling of separate data cubes for proper combination
  4. Assessing schemes for suitable data quality flagging of pixels, planes, and/or entire cubes
  5. Devising methods for arriving at common spatial esolutions, for the case of variable seeing. Depending on the instrument data cube being combined, there may be the added issue of possible wavelength shifts between data cubes (and the need to interpolate).
  6. Obtaining both NIR and optical test observations
  7. Consider instrument specific issues (e.g. detector independent fringes in VIMOS IFU data)
  8. Analyzing the data, testing methods
  9. Writing/debugging/documenting CPL-based code


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.



There is currently no package available against which the new recipes can be evaluated (TBC). The validation will mostly consist of comparing the results with interactive reduction, e.g. for the VIMOS, SINFONI, GIRAFFE IFU observation data.


Institute of Astronomy
Vienna University
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