MERIS

MEdium Resolution Imaging Spectrometer (MERIS) is one of the main instruments on board the European Space Agency (ESA)'s Envisat platform.

This instrument is composed of five cameras disposed side by side, each equipped with a pushbroom spectrometer. These spectrometers use two-dimensional CCDs. One of the sides of the detector is oriented perpendicular to the trajectory of the satellite and simultaneously collects, through the front optics, observations for a line of points at the Earth's surface (or in the atmosphere). The displacement of the platform along its orbit, combined with a short integration time, generate data that can later be used to create two-dimensional images. A light dispersing system separates the various wavelengths (colors) composing the incoming radiation at the entrance of the instrument and directs these on the detector along the second dimension, i.e., along track. These spectrometers acquire data in a large number of spectral bands, but, for technical reasons, only 16 of them are actually transmitted to the ground segment (one of which is required for the low-level processing of the raw data). This instrument thus provides useful data in 15 spectral bands, which are actually programmable in position, width and gain. In practice, these technical characteristics are kept constant most of the time to allow a large number of systematic or operational missions.