The Ocean and Land Colour Instrument (OLCI) was developed in part to provide continuity with measurements made by the Medium Resolution Imaging Spectometer (MERIS) instrument flown aboard the Envisat spacecraft. OLCI is a visible imaging push-broom radiometer with five camera modules that acquire data in 21 spectral bands ranging from 400 to 1200 nm. The field of view of the five cameras is arranged in a fan-shaped configuration in the vertical plane, perpendicular to the platform velocity. Each camera has an individual field of view of 14.2° and a 0.6° overlap with its neighboring camera. The whole field of view is shifted across track by 12.6° away from the Sun to minimize the impact of Sun glint. OLCI is equipped with on-board calibration hardware based on Sun diffusers. There are three Sun diffusers: two “white” diffusers dedicated to radiometric calibration and one dedicated to spectral calibration, with spectral reflectance features.