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Depending on the data record producer, different product requirements may be applied and they are used to evaluate validation results. An often-used way to handle this is to define several levels of requirements where each level is linked to specific needs or priorities. A three-level approach like the following is rather common:

Satellite product levels

Satellite-based products are often described as belonging to the following condensed description of processing levels, each one with different complexity and information content:

A more comprehensive definition of all processing levels is given here: https://www.earthdata.nasa.gov/engage/open-data-services-and-software/data-information-policy/data-levels.

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The extra data products are not included in the CLARA-A2.1 dataset and are calculated specifically within the C3S project as complimentary data for enabling the description of the full surface radiation budget. Notice also that the SDL and SOL products for the ICDR could not be provided by CM SAF because of computer environment limitations in producing all products in the ICDR version of CLARA-A2.1. Once again, we repeat that combining all variables in the “CLARA product family” group logically combines all variables which are needed for the full description of the Energy Budget at the surface.

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The retrieval of the shortwave surface radiation parameters is based on an estimation of the atmospheric transmission and the associated reflected irradiance at the surface. The retrieval of the longwave surface radiation parameters is based on the cloud information from a combination of CLARA-A2.1 cloud products, reanalysis data and topographic information. 

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AVHRR Global Area Coverage (AVHRR GAC) data is the fundamental climate data record (FCDR) used for generation of the seven Surface Radiation Budget datasets, that are presented in the following sub-sections. The detailed description of the algorithm used to generate AVHRR GAC is given in CM SAF ATBD Cloud Products [D5], Section 4.3. Further information on the specific input and auxiliary data can be found in the Algorithm Theoretical Basis Document (ATBD) for this dataset [D1].

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At the time (~2010) when requirements for the CLARA-A2 data record were defined, as described in [D4], there was no guidance available for surface radiation products in the available GCOS-107 document [D6]. Instead, requirements had to be set based on a dialogue with experts and potential users (e.g., in association with CM SAF User Workshops).

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2.1.2 Discussion of requirements with respect to GCOS and other requirements

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New GCOS requirements for the ECV Surface Radiation Budget are summarized in GCOS-200 [D7] and include requirements for the horizontal resolution, temporal resolution, accuracy and stability. However, these requirements are only valid for the net fluxes (i.e., SNS and SNL) and not for all individual radiation budget components (see Table 2-4 below). However, one could claim that individual radiation budget components should consequently be constrained in the same way as net fluxes.

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2.2.2 Key Performance Indicators - KPIs

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The Cloud_cci (A)ATSR data record forms the basis for the calculation of KPIs for the SLSTR based ICDR. The KPIs for the SRB products are based on comparison against the NASA Clouds and the Earth's Radiant Energy System (CERES) instruments (Wielicki et al., 1996). These comparisons are represented as the 2.5 and 97.5 percentiles of the distribution of differences between (A)ATSR or SLSTR monthly-mean values and the corresponding CERES values (corrected for the mean seasonal cycle). These values, calculated from the 12-year (A)ATSR CDR are summarized in Table 2-6.

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2.2.3 Discussion of requirements with respect to GCOS and other requirements

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