Planck Early Results. V. The Low Frequency Instrument data processing

TL;DR

This paper details the data processing pipeline for the Planck Low Frequency Instrument, including calibration, noise estimation, map-making, and beam characterization, crucial for producing the Early Release Compact Source Catalogue.

Contribution

It introduces a comprehensive data reduction and calibration methodology for LFI data, including noise modeling and beam estimation, enhancing the accuracy of Planck's early cosmological results.

Findings

Noise knee frequencies range from 100mHz at 30GHz to tens of mHz at 70GHz.

Effective destriping reduces correlated noise in sky maps.

Main beams are accurately estimated using Jupiter transits.

Abstract

We describe the processing of data from the Low Frequency Instrument (LFI) used in production of the Planck Early Release Compact Source Catalogue (ERCSC). In particular, we discuss the steps involved in reducing the data from telemetry packets to cleaned, calibrated, time-ordered data (TOD) and frequency maps. Data are continuously calibrated using the modulation of the temperature of the cosmic microwave background radiation induced by the motion of the spacecraft. Noise properties are estimated from TOD from which the sky signal has been removed using a generalized least square map-making algorithm. Measured 1/f noise knee-frequencies range from 100mHz at 30GHz to a few tens of mHz at 70GHz. 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 uncertainties on LFI and Planck products are also produced. Main beams are estimated down to the approx -10dB level using Jupiter transits, which are also used for geometrical calibration of the focal plane.