MEdium Resolution Imaging Spectrometer (MERIS) was one of the main instruments on board the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

(ESA)'s

Envisat Envisat ("Environmental Satellite") is a large Earth-observing satellite which has been inactive since 2012. It is still in orbit and considered space debris. Operated by the European Space Agency (ESA), it was the world's largest civilian Ear ...

platform. The sensor was in orbit from 2002 to 2012. ESA formally announced the end of Envisat's mission on 9 May 2012. Envisat image of a phytoplankton bloom in the Baltic Sea ESA226711

Envisat image of a phytoplankton bloom in the Baltic Sea ESA226711

This instrument was composed of five cameras disposed side by side, each equipped with a

pushbroom A push broom scanner, also known as an along-track scanner, is a device for obtaining images with spectroscopic sensors. The scanners are regularly used for passive remote sensing from space, and in spectral analysis on production lines, for exa ...

spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomeno ...

. These spectrometers used two-dimensional

CCD CCD may refer to: Science and technology * Charge-coupled device, an electronic light sensor used in various devices including digital cameras * .ccd, the filename extension for CloneCD's CD image file * Carbonate compensation depth, a property ...

s. One of the sides of the detector was oriented perpendicular to the trajectory of the satellite and simultaneously collected, 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, generated data that was later used to create two-dimensional images. A light dispersing system separated the various wavelengths (colors) composing the incoming radiation at the entrance of the instrument and directed these on the detector along the second dimension, i.e., along-track. These spectrometers acquired data in many spectral bands. For technical reasons only 16 of the bands were actually transmitted to the

ground segment A ground segment consists of all the ground-based elements of a spaceflight, space system used by operators and support personnel, as opposed to the Satellite space segment, space segment and user segment. The ground segment enables management of ...

(one of which is required for the low-level processing of the raw data). This instrument thus provided useful data in 15 spectral bands, which were actually programmable in position, width and gain. In practice these technical characteristics were kept constant most of the time to allow many systematic or operational missions. The intrinsic spatial resolution of the detectors provided for samples every 300 m near

nadir The nadir is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direction opposite of the nadir is the zenith. Et ...

at the Earth's surface, and the pushbroom design avoided or minimized the distortions (e.g., bow tie effects) typical of scanning instruments. This is known as the 'Full Resolution (FR)' product. The more common 'Reduced Resolution (RR)' products were generated by aggregating the FR data to a nominal resolution of 1200 m. The total field of view of MERIS was 68.5 degrees around nadir (yielding a swath width of 1150 km), which was sufficient to collect data for the entire planet every three days (in equatorial regions). Polar regions were visited more frequently due to the convergence of orbits. The primary objective of MERIS was to observe the color of the

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

, both in the open ocean (clear or Case I waters) and in

coast A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...

al zones (turbid or Case II waters). These observations were used to derive estimates of the concentration of

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

and

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s in suspension in the water. It was also used for monitoring and mapping the deposits of seagrass ''

Posidonia oceanica ''Posidonia oceanica'', commonly known as Neptune grass or Mediterranean tapeweed, is a seagrass species that is endemic to the Mediterranean Sea. It forms large underwater meadows that are an important part of the ecosystem. The fruit is free ...

'', in couple with the airborne HR/VHR (High/Very High Resolution) multispectral sensors for correcting the atmospheric and water column noise attenuation of the reflectance signals which arise from the shallow and turbid sea bottom waters in the

Northern Mediterranean Southern Europe is also known as Mediterranean Europe, as its geography is marked by the Mediterranean Sea. Definitions of southern Europe include some or all of these countries and regions: Albania, Andorra, Bosnia and Herzegovina, Bulgaria, C ...

. These measurements are useful to study the oceanic component of the global

carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...

and the productivity of these regions, amongst other applications. The characterization of atmospheric properties (gaseous absorption and

aerosol An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...

scattering) is essential to derive accurate information over the oceans because they contribute to the bulk of the signal measured (under clear skies) or simply because clouds prevent the observation of the underlying surface. In addition, this instrument is useful to monitor the evolution of terrestrial environments, such as the fraction of the solar radiation effectively used by plants in the process of

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

, amongst many others applications.

References

{{reflist

External links

Earth Snapshot
- Web Portal dedicated to Earth Observation. Includes commented satellite images, information on storms, hurricanes, fires and meteorological phenomena.
Miravi
- Meris Image Rapid Visualization. MIRAVI shows the gallery of images generated on the Level0 (raw data) Meris Full Resolution (300m) products, few seconds after their availability.
SRRS
- Satellite Rapid Response System. Like MIRAVI but including also ASAR, MERIS Full and Reduced Resolution and ALOS AVNIR2 images.
ESA page on MERIS
Earth observation satellites Oceanographic satellites Spectrometers Satellite imaging sensors Satellite meteorology

See also

References

External links