The Medium Resolution Imaging Spectrometer (MERIS) was a programmable, medium-spectral resolution imaging spectrometer operating in the solar reflective spectral range. Fifteen spectral bands can be selected by ground command. The instrument scanned the Earth's surface by the so called "push-broom" method. Linear CCD arrays provide spatial sampling in the across-track direction, while the satellite's motion provides scanning in the along-track direction.

MERIS was designed so that it could acquire data over the Earth whenever illumination conditions were suitable. The instrument's 68.5-degree field of view around nadir covered a swath width of 1150 km. This wide field of view was shared between five identical optical modules arranged in a fan shape configuration.

The mission ended on May 9, 2012, after the sudden loss of communication with the Envisat-1 satellite on April 8, 2012.