POLDER (polarization and directionality of the Earth reflectances) is a French instrument that will be flown on- board ADEOS (advanced earth observing satellite) polar orbiting satellite, scheduled to be launched in August 1996. POLDER is a multispectral imaging radiometer/polarimeter designed to collect global and repetitive observations of the solar radiation reflected by the Earth/atmosphere system, with a wide field of view (2400 km) and a moderate geometric resolution (6 km). The instrument concept is based on telecentric optics, on a rotating wheel carrying 15 spectral filters and polarizers, and on a bidimensional CCD detector array. In addition to the classical measurement and mapping characteristics of a narrow-band imaging radiometer, POLDER has a unique ability to measure polarized reflectances at three different polarization angles (for three of its eight visible and near-infrared spectral bands), and to observe target reflectances from 14 different viewing directions during a single satellite pass. All the data transmitted by POLDER are processed in the POLDER Processing Centre. Level 1 products include geometrically and radiometrically corrected data, level 2 products are elementary geophysical products created from a single satellite pass, and level 3 products are geophysical synthesis from several passes of the satellite. This paper presents the radiometrical and geometrical algorithms of the level 1 processing: new algorithms developed for the removal of sensor artefacts (smearing, stray light), for the radiometrical mode inversion (normalized radiance and polarization parameter extraction), and for the geometrical projection of the data on a unique grid are explained.