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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
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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
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Product description
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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
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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)
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Annotation Data Set "Product Quality"
Annotation Data Set "Tie Points Location and corresponding Auxiliary Data"
Global Annotation Data Set
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Level 1b Algorithms
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MERIS User Guide
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 Water Confidence Checks (step 2.6.5)

Water confidence checks include processing of Sun glint, and flagging of low pressure and whitecaps. These steps use the wind and pressure provided in the L1B product annotations. All water confidence checks apply to water pixels within a 4x4 pixels window. Glint processing (step

Glint processing applies only to water pixels

· Glint estimation

The Sun glint reflectance rg is calculated (step by interpolation in LUT produced using the Cox and Munk model (1954) as a function of geometry, wind speed modulus and direction. An estimate of glint reflectance is produced. Wind speed modulus and wind direction are computed from the W_u and W_v annotations.

Note: Sun glint reflectance is now an input to current step as its computation a been moved to section “Pixel identification” (step 2.1c).

· Glint classification (low, medium or high glint ?)

This glint reflectance is compared to a low glint threshold (step If the glint reflectance is below this low glint threshold then no glint correction for this pixel is applied. If the pixel is not bright then it is further processed by step If bright, it is flagged as ice or high aerosol load.

If the glint reflectance is above the low glint threshold then the glint reflectance is compared to a medium glint threshold (step

If the glint reflectance is below the medium glint threshold then a medium glint flag is raised and the pixel is corrected for glint reflectance in step

If the glint reflectance is above the medium glint threshold then no correction is applied and the pixel is flagged as uncorrected sun glint (step

In addition, a specific glint threshold is used to derive a second “high glint” flag dedicated to Water Vapour Processing over water (step As a matter of fact, when the Glint reflectance is very high, total water vapour over water surface is best determined using the Water Vapour Over Land algorithm, best suited for bright underlying surfaces.

· Glint correction in case of medium glint (step

The glint reflectance at surface level is transferred to the Top Of Atmosphere by applying a direct atmospheric transmission term (including Rayleigh scattering on both sun-surface and surface sensor paths). The Top Of Atmosphere glint reflectance rg* is then subtracted from the TOA reflectance.

Note : step, because of its simplicity, is only shown in the corresponding equation section. Low pressure water flagging (step

Surface pressure (from ECMWF annotation) is compared with a threshold in order to flag low pressure, typically high altitude inland waters. Above such waters, the results of the atmosphere correction are disturbed. Whitecaps Flagging (step

The modulus of the wind speed is compared to a threshold. Above that threshold a whitecap flag is raised because white caps are likely to disturb the performance of the atmosphere correction. Reflectance threshold on reflectance at 412 nm (step

An additional “bright” pixels screening, specific to water pixels, is performed by comparison of the Glint corrected reflectance at 412 nm with a pre-computed threshold. It is intended to further sort out and flag those pixels affected by sea-ice, partial clouds or very high aerosol load.

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