Level 2: Geophysical Data Products

The MERIS Level 2 algorithms theoretical basis document
MERIS Level 2 reference product
Product description
Flags
Annotation data set

The MERIS Level 2 algorithms theoretical basis document

The scientific description of the MERIS Level 2 algorithms are described in Algorithm Theoretical Basis Documents (ATBDs). The architecture of the MERIS Level 2 processing is schematically represented in the block diagram below.

Each processing step in the block diagram corresponds to one (or more) ATBDs. ATBDs are identified by red numbers.

The following table contains the chapters of the ATBDs implemented in version 6.04 of the MERIS IPF.

MERIS Level 2 reference product

The classification between land and sea is made on a pixel by pixel basis by using an a priori land sea mask, as in the Level 1b, complemented by spectral signature and radiometric tests to consolidate the classification.

• Ocean pixels are processed with the ocean algorithms on a pixel basis
• Ocean geophysical parameters are retrieved on a pixel basis as well as ocean-normalised water leaving radiances (reflectance)
• Land pixels are processed with the land algorithm using a window approach
• Land surface reflectances are reported on a pixel basis as well as land vegetation indices
• Cloudy pixels are processed with the cloud algorithms on a pixel basis
• Cloud geophysical parameters are retrieved on a pixel basis as well as cloud reflectances
• Partly cloudy pixel over both ocean and a land surfaces will be processes according to their underlying surface type but the underlying surface geophysical parameters will not be provided. The associated reflectances are provided on a pixel basis

The Level 2 classification information will be provided on a pixel by pixel basis in the flag measurement data set.

Product description

For each pixel classification (Ocean/Land/Cloud), the corresponding specific information are defined data sets hereafter.

Note:

Flags

Flags will be provided on a pixel by pixel basis. Level 1b flags will enable the Level 2 processing to switch processing depending on the underlying surface type identified. The following list of flags to be provided by the Level 2 processing have been identified to date:

From Level 1b flags

• Land/sea (a priori)
• Coastline
• Duplicated
• Cosmetic
• Suspect
• Invalid
  

Classification flags

• Land/sea (reclassified)
• Cloud
• High-sun glint
• Thick aerosols
• High inland water
• Dense dark vegetation
• Turbid water
• Yellow-substance-dominated water
  

Quality flags

• Partially cloudy
• Cirrus
• Medium sun glint
• White caps risk
• Anomalous scattering  
  

Out-of-range flags

• Input out-of-range for water vapour processing
• Output out-of-range for water vapour processing
• Input out-of-range for land or cloud or ocean case 1 processing
• Output out-of-range for land or cloud or ocean case 1 processing
• Input out-of-range for ocean case 2 processing
• Output out-of-range for ocean case 2 processing
  

Annotation data set

The MERIS ADS will contain the auxiliary data predicted for the unconsolidated product and actual for the consolidated product.

The localisation information, with respect to the reference WGS084 as well as the altitude and associated localisation shift, will be provided at tie points. These tie points are located every 64 × 64 Full Resolution (FR) pixels in the product grid and are listed in the ADS.

The viewing information (sun zenithal, view zenithal, and azimuthal angles) will be provided at fixed predetermined tie points e.g., every 64 FR pixels across track × 64 FR pixels along track and will be listed in the ADS.

The following resampled auxiliary data will be identified by Data Set Descriptors (DSDs) in the Specific Product Header (SPH) and will be content provided at tie points in the ADS:

• Surface atmospheric pressure fields - ECMWF
• Surface wind speed fields - ECMWF
• Total ozone content fields - ECMWF
• A quality summary will be provided at a subset of tie points

MERIS derived Level 2 products

• The derived Level 2 Cloud (RRC) and the derived Level 2 vegetation products (RRV) consist of only two of the Level 2 data sets. (See spreadsheets)


• The derived Level 2 low resolution product (LRC) consists of a subsampled (4.8km × 4.8.km) Level 2 cloud product.

For further details regarding the MERIS Level 2 data products see Product Spreadsheets.

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