The Medium Resolution Imaging Spectrometer (MERIS) is one of the ten instruments on board the Envisat satellite launched on the 28th of February 2002 from Kourou (French Guyana) and operated by the European Space Agency (ESA). MERIS is a 68.5 deg field-of-view nadir-pointing imaging spectrometer which measures the solar radiation reflected by the Earth in 15 spectral bands (visible and near-infrared). It obtains a global coverage of the Earth in 3 days. Its main objective is to measure the sea colour and quantify the ocean chlorophyll content and sediment, thus providing information on the ocean carbon cycle and thermal regime. It is also used to derive the cloud top height, cloud optical thickness, aerosol and water vapour column. The ground spatial resolution of the instrument is 260 m x 290 m. Only reduced resolution data (1.04 km x 1.16 km) are archived at the NEODC.