18.104.22.168.8 MERIS Level 2 Product Formatting Algorithm
MERIS processed data samples corresponding annotations and flags are collected from previous steps and formatted according to Level 2 product description in R-8.
Each MERIS Level 2 geo-physical product is derived from a MERIS Level 1B product (herein after called "parent L1B product") and auxiliary parameter files specific of the MERIS Level 2 processing.
The MERIS Level 2 product is composed of : the Main Product Header (MPH), the Specific Product Header (SPH), one Summary Quality Annotation Data Sets (SQ ADS) ), one Global Annotation Data Sets (GADS), one Annotation Data Sets and twenty Measurement Data Sets.
The MPH allows to identify the product and some of its main characteristics.
The SPH contains references to external data files and Data Sets descriptors, as well as general information applicable to the product such as sensor characteristics, PCD and metrics summary. A large amount of SPH contents can be directly derived from the parent L1B product SPH.
The first ADS (SQ ADS) contains information on the quality of the product.
The GADS contains all the data scaling factors.
The second ADS contains information on geo-location, measurement viewing and illumination geometry and auxiliary environment parameters for a subset of the product pixels: the tie-points. One ADSR includes the set of tie points corresponding to a given satellite location. It is the same as in the parent Level 1B product.
The Measurement Data Sets (MDS) contain geo-physical parameters derived by the L2 processing. The products are distributed in order to obtain
· maximum homogeneity of the information: the "reflectance" bands, for instance, contain reflectance whatever the underlying surface is;
· maximum storage efficiency: the bytes allocated for a given pixel will be used to store different parameters, relevant to the surface observed.
The Flags MDS (20) contains all information needed to decode and check for quality the distributed pixel information.
One MDSR includes the parameters for all pixels corresponding to a given time sample of MERIS. The term "product line" will be used hereafter to name the MDSRs of the different MDS for the same time sample, i.e. with the same MDSR index.
Information coming either from parent Level 1B product, from external data sources, or generated by any processing step are gathered, organised, scaled and coded according to the “Envisat-1 Products Specifications - Volume 11 – MERIS Products Specifications” document ( R-8) to build the Level 2 product file.