<p>The Copernicus missions Sentinel-4 (S4) and Sentinel-5 (S5) will carry out atmospheric composition observations on an operational long-term basis to serve the needs of the Copernicus Atmosphere Monitoring Service (CAMS) and the Copernicus Climate Change Service (C3S).</p><p>Building on the heritage from instruments such as GOME, SCIAMACHY, GOME-2, and OMI, S4 is an imaging spectrometer instruments covering wide spectral bands in the ultraviolet and visible wavelength range (305-500nm) and near infrared wavelength range (750-775 nm). S4 will observe key air quality parameters with a pronounced temporal variability by measuring NO<sub>2</sub>, O<sub>3</sub>, SO<sub>2</sub>, HCHO, CHOCHO, and aerosols over Europe with an hourly revisit time.</p><p>A series of two S4 instruments will be embarked on the geostationary Meteosat Third Generation-Sounder (MTG-S) satellites. S4 establishes the European component of a constellation of geostationary instruments with a strong air quality focus, together with the NASA mission TEMPO and the Korean mission GEMS.</p><p>This paper will address the development status of the L1b Operational Processor (L1OPS) by EUMETSAT and the supporting L1b reference processor (L1RP) developed by ESA; In dedicated cases (e.g. CTI, Non-linearity signal loss, ...) the algorithms input from the S4 Industrial Prime have been used. The paper will also provide an overview of the status of the Level 2 processor developed by ESA for integration into the EUMETSAT MTG-S ground segment.</p>
