MERIS is a 68.5 degree field-of-view pushbroom imaging spectrometer that measures the solar radiation reflected by the Earth, at a ground spatial resolution of 300m, in 15 spectral bands, programmable in width and position, in the visible and near infra-red. MERIS allows global coverage of the Earth in 3 days.
Taking advantage of the re-processing of MERIS Level 2 (L2) data, a number of demonstration MERIS Level 3 products have been generated for the complete mission. They have been processed using the standard L2 products processed with the 2nd reprocessing version of the IPF, version 5.
The first set of products are marine products:
Chlorophyll Concentration for the open ocean (case I)
Chlorophyll concentration is a very convenient measure of abundance of phytoplankton biomass, which has an important role in fixing CO2 through photosynthesis.
Water leaving radiances at 412, 443, 490, 510 and 560 nm.
Aerosol optical thickness at 865 nm and the angstroem coefficient.
The aerosol retrieval is an important step in the atmopheric correction, but it also gives an indication on the status of the atmosphere (pollution, dust storm...etc).
The second set of products are land products:
The aerosol optical thickness at 443 nm and the angstroem coefficient.
The aerosol properties give information on the air quality and aerosol types over land. It can be used as well to correct the land reflectance from the atmospheric effect.
The MERIS Global Vegetation Index (MGVI)
The MGVI is the Fraction of Absorbed Photosynthetcally Active Radiation (FAPAR) calculated from MERIS data. It is a fundamental parameter for monitoring the state of the vegetation and for environmental studies. It represents the fraction of the solar energy absorbed by the vegetation which is the key parameter for the photosynthetic process.
MERIS Terrestrial Chlorophyll Index
In addition, global and regional composite (Level 3) products of MERIS Level 2 geophysical data have been generated.
The product produces an image of chlorophyll content (i.e. the amount of chlorophyll per unit area of ground). Chlorophyll content plays an important role in determining the physiological status of a plant, is related to photosynthetic rate and varies temporally and spatially. MTCI composites can therefore be used to estimate relative and land cover specific chlorophyll content in space and time.
The MERIS Terrestrial Chlorophyll Index (MTCI) product is available from NEODC
The products are generated in GEOTIFF format, on lat-lon geocoded grids, accompanied by an XML-metadata file and a JPEG browse image. The MTCI is an ESA Level 2 land product which is calculated using three red/near infrared bands of MERIS data.
Albedo is the measure of the reflectivity of the earth surface. It is the ratio of the radiation reflected to the amount of solar radiation incident upon it. The fraction, usually expressed as a percentage from 0% to 100%, is an important concept in climatology. The objective is to derive 16-days averaged maps of spectral and broadband albedos from data acquired by MERIS at a spatial resolution of 0.05° x 0.05°.
The global surface albedo map is used as auxiliary parameters in the ENVISAT Ground Segment and improves the generation of the standard MERIS Level2 atmospheric products. MERIS albedo maps are also used in climate and environmental studies. The follow up product is the GlobAlbedo product (www.globalbedo.org).
The full set of MERIS albedo maps, including relevant documentation, have been made publicly available from the MERIS Global Land Surface Albedo website in March 2008.
The third set of products are atmosphere products:
The water vapour over clear sky
Water vapour is the most effective greenhouse gas in the atmosphere. It influences weather and climate and is responsible for cloud development, precipitation, and modulates the atmospheric radiative energy transfer.
It effects weather and climate and is responsible for cloud development, precipitation, and modulates the atmospheric radiative energy transfer. Therefore, it influences the energy balance of the earth and, in turn, also effects the temperature and circulation of the earth-atmosphere system.
In addition, two other quality products have been processed:
The aerosol optical thickness at 550 nm both over land and sea.
The repartition of the ABSO_DUST flag
The ABSO_DUST flag represents the dust-like absorbing aerosol selected for atmosphere correction.
Acknowledgement: ACRI, JRC, Brockmann Consult, GRID On demand team at ESRIN.