Planck 2013 results. II. The Low Frequency Instrument data processing

We describe the data processing pipeline employed by the Low Frequency Instrument (LFI) data processing centre (DPC) to create and characterize the full-sky maps based on the first 15.5 months of operations at 30, 44 and 70 GHz. In particular, we discuss the various steps involved in reducing the data, starting from telemetry (TM) packets through to the production of cleaned calibrated timelines and calibrate d frequency maps. Data are continuously calibrated using the modulation induced on the mean temperature of the cosmic microwave background radiation by the proper motion of the spacecraft. Sky signals other than the dipole are removed by an iterative procedure based on simultaneous fi tting of calibration parameters and sky maps. Noise properties are estimated from time-ordered data after the sky signal has been removed, using a generalized least square map-making algorithm. A destriping code (Madam) is employed to combine radiometric data and pointing information into sky maps, minimizing the variance of correlated noise. Noise covariance matrices, required to compute statistical uncertainti es on LFI and Planck products, are also produced. Main beams are estimated down to the≈−20 dB level using Jupiter transits, which are also used for th e geometrical calibration of the focal plane.