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Reference documents
MERIS Product Handbook
MERIS Product Handbook
MERIS Product Handbook
MERIS Credits
MERIS Data Formats Products
MERIS Glossary and reference documents
Optics Glossary
Vegetation Glossary
Water Vapour Glossary
Ocean Colour Glossary
Neural Network Glossary
Meteorology Glossary
Cloud Glossary
Atmosphere Glossary
Product Glossary
Geometry Glossary
Acronyms and Abbreviations
MERIS Instrument
Instrument Characteristics and Performance
MERIS Quality Status
Instrument characteristic
Characterisation and Calibration
Onboard Calibration Hardware
Calibration Modes
Instrument Description
Instrument model philosophy
Instrument Concept
Digital processing Unit
Video Electronic Unit
Detection Focal Plane
Instrument optics
The MERIS instrument
MERIS Products and Algorithms
Auxiliary Files
Common Auxiliary Datasets
Auxiliary Datasets for Level 2 Processing
Auxiliary Datasets for Level 1b Processing
Summary of Auxiliary Datasets
Water Vapour Parameters Data File
Atmosphere Parameters Data File
Level 2 Control Parameters Data File
Aerosol Climatology Data File
Coastline/Land/Ocean Data File
Digital Roughness Model Data File
Radiometric Calibration Data File
MERIS Level 1b Control Parameters Data File
Digital Elevation Model
ECMWF Data Files
ENVISAT Orbit Data Files
Surface Confidence Map File
Land Vegetation Index Parameters Data File
Cloud Measurement Parameters Data File
Ocean II Parameters Data File
Ocean I Parameters Data File
Land Aerosols Parameters Data File
Ocean Aerosols Parameters Data File
MERIS Instrument Data File
MERIS-Specific Topics
Level 2 Products and Algorithms
Level 2 Products
Level 2 Geophysical Products
Annotation data set
Water Vapour products
Land products
Meris Terrestrial Chlorophyll Index
Meris Global Vegetation Index
Aerosol Angström Coefficient
Aerosol optical thickness
Cloud products
Cloud reflectance
Cloud Type
Cloud top pressure
Cloud albedo
Cloud optical thickness
Ocean products
The MERIS Aerosol Angström Coefficient
Aerosol optical thickness
Photosynthetically Active Radiation (PAR)
Yellow substance
Suspended matter
Algal Pigment Index II
Algal Pigment Index I
Normalized water leaving radiance / reflectance
Product description
Level 2 High-Level Organisation of Products
Full Resolution Geophysical Product
Extracted Vegetation Indices
Extracted Cloud Thickness and Water Vapour for Meteo Users
Extracted Cloud Thickness and Water Vapour
Reduced Resolution Geophysical Product
Level 2 Algorithms
Level 2 Accuracies
Level 2 Algorithm Description
MERIS Level 2 Product Formatting Algorithm
Measurement Data Sets
Annotation Data Set "Tie Points Location and corresponding Auxiliary Data"
Global Annotation Data Set - Scaling Factors
Annotation Data Set "Summary Product Quality"
Specific Product Header
Main Product Header
MERIS Land Pixels Processing
MERIS Bottom Of Atmosphere Vegetation Index (BOAVI) (step 2.8)
Atmospheric correction over land (step 2.6.23)
MERIS Top Of Atmosphere Vegetation Index (TOAVI) (step 2.2)
Water Processing
MERIS Ocean Colour Processing (step 2.9)
Clear water atmospheric corrections (step 2.6.9)
Turbid water screening and corrections (steps 2.6.8, 2.6.10)
Water Confidence Checks (step 2.6.5)
Cloud Processing
Cloud type processing (step 2.4.8)
Cloud Optical Thickness processing (step 2.4.3)
Cloud Albedo processing (step 2.4.1)
Total Water Vapour Retrieval
Water vapour polynomial (function)
Range checks (steps 2.3.0, 2.3.6)
Water vapour retrieval over clouds (step 2.3.3)
Water vapour retrieval over water surfaces (steps 2.3.2, 2.3.5)
Water vapour retrieval over land surfaces (step 2.3.1)
MERIS Pixel Identification
Land Identification (step 2.6.26) and Smile Effect Correction (step 2.1.6)
Gaseous absorption corrections (step 2.6.12)
Stratospheric Aerosol Correction (step 2.1.9)
Cloud screening (steps 2.1.2, 2.1.7, 2.1.8)
MERIS Pressure Processing
Atmospheric pressure confidence tests (steps 2.1.2)
Atmospheric pressure estimate (steps 2.1.5, 2.1.12)
MERIS Pre-processing
Pre processing step
Level 1b product check
Level 2 Physical Justification
Level 1b Products and Algorithms
Level 1b product definition
Browse Products
Level 1b Essential Product Confidence Data
Level 1b Engineering Quantities
Level 1b Accuracies
Level 1b High-Level Organisation of Products
Measurement Data Sets
Annotation Data Set "Product Quality"
Annotation Data Set "Tie Points Location and corresponding Auxiliary Data"
Global Annotation Data Set
Specific Product Header
Main Product Header
Full Resolution Geolocated and Calibration TOA Radiance
Reduced Resolution Geolocated and Calibration TOA Radiance
Level 1b Algorithms
External Data Assimilation
Pixel Classification
Stray Light Correction
Radiometric Processing
Saturated Pixels
Source Data Packet Extraction
Level 0 Products
Product Evolution History
Definitions and Conventions
Notations and Conventions
Product Grid
Organisation of Products
MERIS product data structure
File naming convention
Acquisition identification scheme
Product identification scheme
Latency, Throughput and Data Volume
MERIS products overview
MERIS product types
Full and reduced resolutions
MERIS product processing levels
MERIS User Guide
Image gallery
How to Use MERIS Data
Software Tools
General Tools
How to Choose MERIS Data
Summary of Applications vs. Products
Special Features of MERIS
Geographical Coverage
Principles of Measurement
Scientific Background
Mission Objectives
MERIS Level 3 products
Geophysical Measurements
MERIS Product Handbook
Site Map
Frequently asked questions
Terms of use
Contact us

The ocean exerts a major influence on the Earth's meteorology and climate through its interaction with the atmosphere. Understanding the transfer of moisture and energy between ocean and atmosphere is therefore a scientific priority. Better observations are needed, to improve the accuracy of weather forecasts of marine conditions and the assessment of climatic change.

Earth observation satellites have revolutionised the study of the ocean. They now provide detailed repetitive measurements over remote areas of the world, where previously there were only a limited number of (isolated) observations from ships and buoys. Microwave instruments, including SARs and radar altimeters, have a remarkable sensitivity to the roughness and height of the ocean surface, enabling the detection of ocean currents, fronts and internal waves, oil slicks and ships, as well as accurate measurement of sea level changes, wave height and wind speed. Optical instruments provide measurements of ocean colour and temperature, which are important indicators of phytoplankton, yellow substance and suspended sediments.

ENVISAT, by including advanced SAR, radar altimeter, ocean colour and ocean temperature instruments together on the same platform, offers particularly exciting opportunities for synergetic measurements over the oceans. It provides an improvement in measurement capability compared with ERS, together with possibilities for many new geophysical measurements. The simultaneous recording of MERIS ocean colour measurements with both AATSR sea surface temperature, and ASAR sea surface roughness offers particularly exciting possibilities.

Ocean Biophysical Properties

There remain major uncertainties about the amount of carbon stored in the ocean and the biosphere, and about the fluxes between these reservoirs and the atmosphere. In particular, there is an important need for better information on the spatial distribution of biological activity in the upper ocean and its temporal variability, especially in the case of oceanic phytoplankton biomass, which has an important role in fixing CO2 through photosynthesis. In the upper layers of the open ocean, chlorophyll concentration is the most convenient index for phytoplankton abundance and this can be measured using the visible part of the spectrum.

"The remote measurement which has caused the greatest interest within the JGOFS (Joint Global Ocean Flux Study) is the estimation of basin and global-scale variability in the concentration of chlorophyll in the upper ocean. The images of the global distribution of these pigments, derived from data taken by the coastal zone colour scanner (CZCS) onboard the United States' Nimbus-7 spacecraft, have revolutionised the way biological oceanographers view the oceans. For the first time, the blooming of the ocean basins in spring has been observed, as has the extent of the enriched areas associated with the coastal ocean." (International Geosphere-Biosphere Programme [IGBP] A study of Global Change, Report No. 12, 1990).

Although CZCS, launched in 1978, was intended as a one-year proof-of-concept mission, the sensor continued to transmit data over selected oceanic test sites until early 1986. The figures below show examples of CZCS chlorophyll maps of the Earth and the Mediterranean Sea.

Remotely sensed information about global ocean colour is once again available; firstly from the OCTS and POLDER instrument on the Japanese ADEOS mission, from the NASA SeaWiFS satellite launched in August 1997, and from the MOS instrument on IRS-3. MERIS provides data continuity with improved spectral and spatial performance. This results from the use of several near-infrared channels to perform atmospheric corrections, and several narrow visible channels to compute radiance values.

Phytoplankton abundance varies from less than 0.03 mg m-3 in oligotrophic waters (i.e., waters poor in nutrients and therefore in phytoplankton), up to about 30 mg m-3 in eutrophic waters (i.e., in nutrient rich waters, supporting high biomass). Ocean colour responds in a non-linear way to these large changes in chlorophyll content. It is conveniently depicted by the ratio of blue-to-green radiation backscattered by the ocean, with the ratio that is most sensitive based on wavelengths of 445 and 565 nm. It varies within a range of 1 to 20 for the types of pigments considered, and decreases, almost linearly, with the logarithm of the concentration.

Coastal Waters

The coastal regions are the most populated areas in the world and coastal waters are highly affected by human activities. Marine ecosystems are affected by the influx of large amounts of agricultural and industrial pollutants and sewage from rivers which may inhibit or stimulate marine productivity.

Continuous long-term observation of coastal waters, which cover more than three million square kilometres, is most important for regional climate impact studies and for environmental monitoring. Remote sensing measurements from satellite are the only available means of monitoring such large areas of water.

The major water constituents, which determine the marine and estuarine ecology and the bio-geochemical budget and whose concentration and distribution can be determined by optical remote sensing, are suspended matter, phytoplankton and Gelbstoff.

Figure 1.10 - Simulated multispectral radiances for a spectral resolution of 5 nm just above the water surface

Suspended matter is defined as a combination of:

· inorganic particles and detritus, present due to re-sedimentation and advection processes

· atmospheric inputs

· dead material of plankton

Gelbstoff consists of various polymerised dissolved organic molecules which are formed by the degradation products of organisms. These originate in brackish and underground water as well as in extraordinary plankton blooms. All these constituents have different optical properties, but there are similarities in their spectral scattering and absorption coefficients.

The upward radiance at any visible wavelength is composed of contributions from all these substances. Figure 1.9 above shows simulated multispectral radiances for different ocean waters. Suspended matter usually enhances the upward radiances through reflection within the visible spectrum, while Gelbstoff reduces these radiances mainly in the blue.

To convert from the optical properties of the water constituents, used in the radiative transfer model, to pigment or suspended matter concentration units, robust algorithms have been developed with global applicability. The accuracy of derived oceanic properties depends strongly on the precision of the atmospheric correction procedure.

The development of inverse modelling techniques for the interpretation of MERIS measurements is an ongoing process. For monitoring coastal regions world wide, precise multispectral radiances, with contemporary optical and concentration measurements of the water constituents, are needed. As well as the chlorophyll concentration and several atmospheric parameters, planned geophysical products include total suspended matter and yellow substance concentration.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry