GALFACTS Data Processing Pipeline
The Galactic ALFA Continuum Survey (GALFACTS) is a large-area spectro-polarimetric survey being carried out with the Arecibo Radio telescope in Puerto Rico. It uses the seven-beam focal plane feed array receiver system (ALFA) recently installed at Arecibo to carry out an imaging survey project of the 12,700 square degrees of sky visible from Arecibo at 1.4 GHz. The raw data produce by spectrometer creates fifty-six digital data streams (seven beams, four polarization states and two frequency bands) each with 4096 spectral channels sampled at 1 millisecond. The aggregate data rate is 460 MB/s.
The data processing pipeline for the GALFACTS observations consists of two parts: (i) the derivation of parameters necessary for processing of the GALFACTS main run data using the calibration observations, and (ii) processing of the main run data to create calibrated spectral image cubes converted to Stokes parameters (I, Q, U, V ). Thus, the imaging process consist of mapping the time-frequency observations to sky coordinate-frequency data cubes. This process is computationally expensive, and involves many calibration and transformation steps, which will be discussed in detail here. Being a first of its kind survey ever attempted, the data processing offers significant challenges right from dealing with a very large data-set to the fact that new techniques need to be developed to reduce such a data-set. The multi-beam nature of observations requires significant modifications of the traditional data reduction techniques for single feed, single dish data. In this talk we will cover all these aspects of the GALFACTS data processing pipeline.
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