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- skymaps 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 calibrated frequency maps. Data are continuously calibrated using the modulation induced on the mean temperature of the cosmic microwave backgroundradiation by the proper motionof the spacecraft. Skysignals other than the dipole are removed by an iterative procedure based on simultaneous fitting of calibration parameters and skymaps. Noise properties are estimated from time-ordered data after the skysignal has been removed, using a generalized least squaremap-making algorithm. A destriping code ( Madam) is employed to combine radiometric data and pointing information into skymaps, minimizing the variance of correlated noise. Noise covariance matrices, required to compute statisticaluncertainties 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 the geometrical calibration of the focal plane.