The GPI IFS data reduction pipeline has the following top level requirements:
The data pipeline comprises several main components, all written in IDL:
When running, the DRP constantly looks for data to reduce, either in the form of new FITS files (in “automatic” mode, used for real-time analysis while observing) or new reduction “recipes” (in regular mode for post-observing analysis). Output data, like the input, are saved as FITS files. Reduced calibration files are stored in a special Calibrations Database directory allowing appropriate calibrations to be retrieved automatically at each step of data reducion. As the pipeline processes data, it can also display plots or figures on screen, or send data to the GPItv display and data analysis tool for interactive exploration of images and spectra. An administration console provides a status display of the data reduction process, and keeps a log of all messages generated during reduction.
The most complex step in the data reduction is the conversion from 2D raw IFS frames to 3D datacubes. Because the light from each lenslet in the IFS is dispersed across many detector pixels, the process of uniquely assigning flux from detector pixels back to GPI’s field of view is complex. This is called ‘Data-cube Extraction’. The overall process is similar for both spectral and polarimetry modes, though algorithmic details differ.
For each mode (prism+filter choice), a map of the reimaged lenslet array geometry must be made based on observations of calibration lamps (e.g. the locations and wavelength solutions of the ~37000 microspectra). This calibration data is produced from arc lamps for use in the extraction process. These calibrations should be moderately stable, and obtaining the necessary lamp data is expected to be part of Gemini’s facility calibrations rather than requiring calibration by individual users. Photometric, spectral, and polarimetric standards must be observed at night in the usual manner. The GPI IFS Data Pipeline is designed to reduce all of this calibration data, and to reduce scientific data to the level where an astronomer can begin custom analyses.