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The Medium Resolution Imaging Spectrometer (MERIS) forms part of the core instrument payload of ESA's environmental research satellite ENVISAT-1. MERIS is funded by ESA. The demands of the European scientific community for a global environmental monitoring system, whose technical characteristics enable the extraction of quantitative information from ocean colour data, as well as for documentation of the state and evolution of the atmosphere and land surfaces, led to the conception of MERIS.
The oceanographic mission is radiometrically the most demanding in terms of low radiance levels and their associated high signal-to noise ratios. Therefore, the instrument must be capable of detecting the low levels of radiation emerging from the ocean (linked to the water constituents by the processes of absorption and scattering). But at the same time, for the acquisition of e.g. cloud and land information, the instrument must have a high dynamic range in order to detect bright objects. The characteristics of MERIS are also of great value for the retrieval of information on land surfaces, in particular that of global biomass.
MERIS is a wide field-of-view pushbroom imaging spectrometer with a swath width of 1150km (field-of-view (FOV) = 68.5°) measuring the solar radiation reflected by the Earth in 15 spectral bands from about 412.5nm to 900nm (ESA 1996, http://envisat.esa.int/instruments/meris/). All bands are programmable in width (variable between 1.25 and 30 nm) and position, but are fixed before launch in response to the recommendations of the Science Advisory Group (SAG) for the main period of the mission (see Table 1).
The most crucial requirements for MERIS is the radiometric performance
because signals coming from the ocean are weak while signals emanating
from clouds or land surfaces are strong. A radiometric resolution of 0.03
mWm-2sr-1nm-1 is required to discriminate a pigment concentration of 1mg/m3
. For ocean applications a total signal of about 50 mWm-2sr-1nm-1 (including
the atmosphere) is expected at the sensor at a solar zenith angle of 40°
from the sub-satellite point around 450nm assuming low chlorophyll concentrations.
This requires a dynamic range of more than 3 magnitudes. Taking into account
that MERIS is designed to monitor all targets on Earth a much higher dynamic
range is required and realised.
Each MERIS pixel has a field of view of 0.019°. Due to the wide instrument field of view (68.5°), spatial sampling varies in the across track direction, between 0.26 km at nadir and 0.39 km at swath extremities. Along-track sampling is close to 0.29 km.
MERIS has the capability to output data sampled at the Full Resolution (FR) with the spatial sampling described above, and Reduced Resolution (RR) data sub-sampled at 1.2 km.
For more information on value-added products, please see the MAPP - Algorithm Theoretical Basis Document (PDF, 16MB) or visit the MERIS Application and Regional Products Project (MAPP) website.
"Quicklook" images of the most recently acquired MERIS images are currently available on-line. Please click here to view them and get more information on the MERIS data received and processed by DLR-DFD.
ENVIronment SATellite (launched March 2002).
Envisat, an advanced polar-orbiting Earth observation satellite, provides measurements of the atmosphere, ocean, land, and ice. Instruments include MERIS, AATSR, MWR, GOMOS, MIPAS and SCIAMACHY.
The Envisat satellite has an ambitious and innovative payload that will ensure the continuity of the data measurements of the ESA ERS-1 and ERS-2 satellites. Envisat data supports earth science research and allows monitoring of the evolution of environmental and climatic changes. (http://envisat.esa.int/m-s/).
If you would like to know more about the MERIS instrument or especially the MERIS data available now and in the near future at WDC-RSAT, please contact: email@example.com.