Contributors: O. Bobryshev (DWD)
Issued by: DWD/ Oleksandr Bobryshev
Date: 09/06/2021
Ref: C3S_D312b_Lot1.3.5.1-v2.1_202007_PUGS_ECVSurfacRadiationBudget_v1.0
Official reference number service contract: 2018/C3S_312b_Lot1_DWD/SC1
History of modifications
List of datasets covered by this document
Related documents
Acronyms
General definitions
In the scope of the Copernicus Climate Change Service (C3S), two Surface Radiation Budget datasets are combined into one Climate Data Record (CDR) called "CLARA product family".
The first dataset, EUMETSAT's CM SAF CLARA-A2.1, is the core of this CDR. The second dataset includes extra data products that are not included in the CLARA-A2.1 dataset. The core data products are brokered from CM SAF. The extra net fluxes are not included in the brokered CLARA-A2.1 dataset and are calculated specifically within the C3S project as complimentary data for the convenience of users. Their format is as close as possible to the CLARA-A2.1 and the datasets are meant to be used together. Both datasets are frequently updated with Interim Climate Data Records (ICDRs) or simply extensions, generated using the same software and algorithms to cover more recent periods. The ICDR part for all products covers period from 2019 to 2020.
This separation into two datasets is necessary to keep the origin of the data, e.g. licence affiliations: "EUMETSAT's CM SAF" and "C3S", clear for individual products (Table 1)
Table 1: Licence overview of the CLARA product family Surface Radiation Products available through the CDS
Year | CDR Type | CLARA Product Family | |||
SIS | SDL, SOL | SRS | Net Fluxes | ||
| Longwave fluxes | Extra data products | |||
1982 – 2018 | TCDR | CM SAF (CLARA A2.1) | CM SAF (CLARA A2.1) | C3S | C3S |
2019 – 2020 | ICDR | CM SAF | C3S | C3S | C3S |
The longwave fluxes are not included in the CM SAF ICDR plans for the current phase. To ensure the dataset integrity and continuity, they are calculated within the C3S for the ICDR part. As such, the longwave fluxes change their licence affiliation, namely they are provided within the C3S project for the ICDR part (2019-2020) and are brokered from EUMETSAT’s CM SAF for the TCDR part (1982 to 2018).
Furthermore the CM SAF CLARA-A2.1 dataset has a temporal coverage of January 1982 to June 2019 (as described in [D2]), but TCDR data are only being brokered to the CDS up to December 2018. Data available from the CDS for January 2019 to December 2020 are brokered/derived from the CLARA A2.1 ICDR1.
In contrast to the original CM SAF CLARA-A2.1 dataset, the brokered service within Copernicus solely provides:
- Level-3 data – excluding the level-2b data format.
- Data on a global equal angle grid – excluding the polar grid format.
- An aggregated version of all satellite data – excluding the provision of the individual satellite datasets.
Scope of the document
This is the Product User Guide and Specification (PUGS) document for the CLARA Product Family CDR. It describes data products and data usage, lists target requirements and provides data access information. The data origin overview for all data products is given.
The brokered service within Copernicus solely refers to the CM SAF Validation Report. It can be found at the CM SAF web site http://www.cmsaf.eu with the copy of the main documents provided at the CDS website.
Extra data products produced within C3S are described in this document.
Executive summary
The brokering service of the CLARA-A2.1 data products includes 37 years (1982-2018) of level-3 data (monthly means) on a regular global latitude-longitude grid (with 0.25° x 0.25° resolution), merged from various polar orbiting satellites. It includes three products: the Surface Incoming Shortwave radiation (SIS), the Surface Outgoing Longwave radiation (SOL), and the Surface Downwelling Longwave radiation (SDL). SIS daily averages are also available within C3S. This document refers to the CM SAF documentation [D2] data products and data usage, lists target requirements and provides data access information.
The extra data products (produced specifically within the C3S project) are: the Surface Reflected Shortwave radiation (SRS), the Surface Net Shortwave radiation (SNS), the Surface Net Longwave radiation (SNL), and the Surface Radiation Budget (SRB). Data product descriptions for these extra data products are provided within this document.
The CLARA ICDR is a continuation of the products of the CLARA-A2.1 and the extra data products. It extends both products by 2 years (2019-2020) and further updates.
Table 2: Association table of CLARA product names and CF Standard names used in the CDS (Climate Data Store)
CLARA Long Names | CF Standard names |
Surface Incoming Shortwave Radiation (SIS) | Surface downwelling shortwave flux |
Surface Downwelling Longwave Radiation (SDL) | Surface downwelling longwave flux |
Surface Outgoing Longwave Radiation (SOL) | Surface upwelling longwave flux |
Surface Reflected Shortwave (SRS) | Surface upwelling shortwave flux |
Surface Net Shortwave Radiation (SNS) | Surface net downward shortwave flux |
Surface Net Longwave Radiation (SNL) | Surface net downward longwave flux |
Surface Radiation Budget (SRB) | Surface net downward radiative flux |
1. Data origin and licensing overview
In the scope of the Copernicus Climate Change Service (C3S), two Surface Radiation Budget datasets are combined into one Climate Data Record (CDR) called the "CLARA product family".
The first dataset, CLARA-A2.1, is the core of this CDR. The second dataset includes extra products that are not included in the CLARA-A2.1 CDR. The core data products are brokered from EUMETSAT's CM SAF. The extra data products are not included in the brokered CLARA-A2.1 dataset and are produced specifically within the C3S project as complimentary data for the convenience of users. The longwave fluxes are not included in the CM SAF ICDR plans, so to ensure the dataset integrity and continuity, they are calculated within the C3S for the ICDR part (2019-2020). As such, the longwave fluxes change their license affiliation from CM SAF to C3S for the ICDR part.
The extra data products are meant to be used together with CLARA-A2.1, they have file format and data parameters compatible with to CLARA-A2.1. This separation into two datasets is necessary to keep the origin of the data, e.g. license affiliations: "EUMETSAT's CM SAF" and "Copernicus", clear for individual products. Table 1 in the General definition section gives an overview for the license attribution of all products within this CDR.
The CDR provided here includes daily and monthly means of surface radiation properties on a regular global latitude-longitude grid, merged from various satellites. The TCDR comprises 37 years of data ranging from January 1982 to December 2018. The ICDR part extends the dataset by two more years: from January 2019 to December 2020.
In the TCDR, the data products brokered from CLARA-A2.1 are the Surface Incoming Shortwave radiation (SIS), the Surface Outgoing Longwave radiation (SOL), and the Surface Downwelling Longwave radiation (SDL). In the ICDR, Surface Incoming Shortwave radiation (SIS) is brokered from CLARA-A2.1, while the Surface Outgoing Longwave radiation (SOL), and the Surface Downwelling Longwave radiation (SDL) are generated with the C3S project, using CLARA-A2.1 input data. Therefore, as mentioned above, SOL and SDL for the ICDR part (2019-2020) change their license affiliation from CM SAF to C3S..
The extra data products are generated within C3S_312b Lot1 by the German Meteorological Service, Deutscher Wetterdienst (DWD). They consist of the Surface Reflected Shortwave radiation (SRS), the Surface Net Shortwave radiation (SNS), the Surface Net Longwave radiation (SNL) and the Surface Radiation Budget (SRB).
Note that the brokered service provides a subset of the original CLARA-A2-1 dataset, thus the mentioned products do not cover the entire range of surface radiation budget products contained in the original dataset.
2. Product description
This section provides the specific product description.
Table 3 shows a summary of the general product characteristics.
Table 3: Common characteristics of the brokered part of CM SAF Surface Radiation Budget of AVHRR CLARA-A2.1 and ICDR data
Characteristics | Description |
Originating satellite sensor type | AVHRR Advanced Very High Resolution Radiometer with 4 to 6 VIS-IR channels |
Data class | Earth Observation Data |
Algorithm description reference | CM SAF ATBD Radiation [D1] |
Geographic coverage | Global |
Horizontal grid | 0.25° longitude x 0.25° latitude |
Temporal resolution | Monthly. Monthly and daily for the Surface Incoming Shortwave Radiation |
Main variable | Surface radiation |
Data format | CF-compliant NetCDF |
Algorithm Level 3 processor | CM SAF GAC L3_V2.0 |
2.1 Surface Incoming Shortwave Radiation (SIS)
The brokered version of the CLARA-A2-1 SIS dataset contains daily and monthly means (level-3 data) on a global equal angle grid. The algorithm used to generate the product is outlined in CM SAF ATBD [D1], Section 2.1.1 and CM SAF ATBD ICDR [D8], Section 2.1.1
2.2 Surface Downwelling Longwave Radiation (SDL)
The brokered version of the CLARA-A2 surface downwelling longwave radiation dataset contains monthly means (level-3 data) on a global equal angle grid. The algorithm used to generate the product is outlined in CM SAF ATBD [D1], Section 2.2.1.
SDL is not included in the CM SAF ICDR plans for the current phase, so, for the ICDR dataset (2019-2020), SDL has been produced within the C3S contract.
Reanalysis data are a key input requirement for SDL product. The ERA-Interim reanalysis dataset (used for the TCDR) ended in August 2019, so for the whole ICDR period (2019-2020) ERA-5 data are used. Other input and auxiliary data used for the ICDR are the same as for the TCDR.
2.3 Surface Outgoing Longwave Radiation (SOL)
The brokered version of the CLARA-A2 surface outgoing longwave radiation dataset contains monthly means (level-3 data) on a global equal angle grid. The algorithm used to generate the product is outlined in CM SAF ATBD [D1], Section 2.2.2.
SOL is not included in the CM SAF ICDR plans for the current phase, so, for the ICDR dataset (2019 2020), SOL has been produced within the C3S contract.
Reanalysis data are a key input requirement for SOL product. The ERA-Interim reanalysis dataset (used for the TCDR) ended in August 2019, so for the whole ICDR period (2019-2020) ERA-5 data are used. Other input and auxiliary data used for the ICDR are the same as for the TCDR.
2.4 Surface Reflected Shortwave Radiation (SRS)
The SRS product is generated from the Surface Incoming Shortwave Radiation (SIS) from EUMETSAT’s CM SAF CLARA-A2.1 [D1] and the Surface Albedo (SAL) from CLARA-A2.1 dataset (monthly means). SRS ICDR is generated in the same way as TCDR.
2.5 Surface Net Shortwave Radiation (SNS)
The SNS product is generated from the Surface Incoming Shortwave Radiation (SIS) from EUMETSAT’s CM SAF CLARA-A2.1 [D1] and the Surface Reflected Shortwave Radiation (SRS). SNS ICDR is generated in the same way as TCDR.
2.6 Surface Net Longwave Radiation (SNL)
The SNL product is generated from the Surface Downwelling Longwave radiation (SDL) and the Surface Outgoing Longwave radiation (SOL) brokered from EUMETSAT’s CM SAF CLARA-A2 [D1]. SNL ICDR is generated in the same way as TCDR.
2.7 Surface Radiation Budget (SRB)
The SRB product is generated from the SNS and the SNL, described above.
3. Target requirements
A general overview of user requirements needed for climate monitoring is provided in CM SAF Product Requirements Document [D4]. They were formulated in a dialogue with experts and potential users when there was no guidance from GCOS documents for surface radiation products.
New GCOS requirements for the ECV Surface Radiation Budget are summarized in GCOS-200, Table 23, page 279 and include requirements for the horizontal resolution, temporal resolution, accuracy and stability. GCOS targets are:
- Frequency: Monthly (resolving diurnal cycle)
- Resolution: 100 km
Measurement uncertainty: \( 1\ W/m^2 \) on global mean
Stability: \( 0.2\ W/m^2dec \)
However, these requirements are only valid for the net fluxes (i.e., SNS and SNL) and not for all individual radiation budget components. Having said that, one could claim that individual radiation budget components should consequently be constrained in the same way as net fluxes.
All products in the brokered CLARA-A2.1 dataset fulfil the GCOS requirements regarding the horizontal and temporal resolution. However, the SNS and SNL products do not fulfil the new requirements on accuracy and stability which are very stringent. Nevertheless, achieved accuracy and stability results [see D6] allow consistent quantification of mean values, anomalies, variability and the Earth energy budget in general. We point out the existing uncertainties in the methodology of comparison with area-to point measurements (i.e. satellite-area to point-ground-based reference networks) as important reasons for not fulfilling the new GCOS requirements.
3.1 Surface Incoming Shortwave Radiation
A complete TCDR evaluation of the SIS daily and monthly means is outlined in CM SAF Validation Report [D3], Sections 5.2, 5.2.1 and 5.2.2.
A summary on the accuracy evaluation is given in CM SAF Validation Report [D3], Tables 5-1 and 5-2. Summary on the stability evaluation is given in CM SAF Validation Report [D3], Figure 5-3.
ICDR Accuracy and stability evaluations are given in CM SAF Validation Report ICDR [D10].
Achieved accuracy and stability fulfil the CM SAF product requirements [D4].
3.2 Surface Downwelling Longwave Radiation
The predefined requirements for the SDL are given in CM SAF Product Requirement Document [D4], Annex A. A complete evaluation of the SDL TCDR is outlined in CM SAF Validation Report [D3], Section 5.4. The accuracy estimation of SDL ICDR extension is performed within the C3S using the algorithms developed by CM SAF.
Summary on the TCDR accuracy evaluation is given in CM SAF Validation Report [D3], Table 5-4. Summary on the TCDR stability evaluation is given in CM SAF Validation Report [D3], Figure 5-12.
Achieved accuracy and stability fulfil the CM SAF product requirements [D4]..
3.3 Surface Outgoing Longwave Radiation
The predefined requirements for the SOL are given in CM SAF Product Requirement Document [D4], Annex A. A complete evaluation of the SOL TCDR is outlined in CM SAF Validation Report [D3], Section 5.3. The accuracy estimation of SOL ICDR extension is performed within the C3S using the algorithms developed by CM SAF.
Summary on the TCDR accuracy evaluation is given in CM SAF Validation Report [D3], Table 5-3. Summary on the TCDR stability evaluation is given in CM SAF Validation Report [D3], Figure 5-8, page 24.
Achieved accuracy and stability fulfil the CM SAF product requirements [D4].
3.4 Surface Reflected Shortwave Radiation
Target requirements are not applicable for these products as they are directly derived from other products. All input products fulfil their corresponding target requirements. For this dataset, we provide an accuracy estimation using the error propagation method [D6]. We provide the most conservative accuracy estimation by assuming that the uncertainties in the input datasets align perfectly and fully contribute to the overall uncertainty.
3.5 Surface Net Shortwave Radiation
Same as 3.4
3.6 Surface Net Longwave Radiation
Same as 3.4
3.7 Surface Radiation Budget
Same as 3.4
4. Data usage information
4.1 Data format
Information on the file format for the data brokered from EUMETSAT’s CM SAF CLARA-A2.1 products is provided in CM SAF PUM Surface Radiation Products [D2], Section 4.1.
CLARA product family Global Surface Radiation Budget dataset from polar orbiting satellites is provided in NetCDF (Network Common Data Format) file format. The global attributes follow the Copernicus Common data Model (CDM) instructions [D5]. The metadata and naming definitions follow the Climate & Forecast (CF) conventions version 1-7 (https://cfconventions.org). The keywords follow GCMD Science Keywords (Global Change Master Directory), Version 8.1.
ICDR extensions of SOL and SDL and the extra data products data format and data file contents are made fully compatible with brokered CLARA-A2.1 products.
4.2 Product content and attributes
A description of the file contents of the brokered CLARA-A2.1 dataset in general is given in CM SAF PUM [D2], Section 4.1. Note that within the scope of this project, the brokered dataset exclusively comprises level-3 data on a global equal angle grid.
Each NetCDF file consists of dimensions, variables and attributes. All data files are built following the same design principles. Each data file contains the following coordinate and 3-dimensional variables:
- Time
Start of averaging time period [days since 1970-01-01 00:00:00]
- Latitude
Geographical latitude of grid-box centre [degrees_north]
- Longitude
Geographical longitude of grid-box centre [degrees_east]
- \( SIS,\ SDL,\ SOL,\ SRS,\ SNS,\ SNL,\ SRB \)
Parameter grid box mean value, name depends on the parameter
Global attributes are summarized in the Copernicus CDM [D5], Section 9.
ICDR extensions of SOL and SDL and the extra data products NetCDF file structure is fully compatible with brokered CLARA-A2.1 products.
4.3 User-relevant dataset characteristics
The product description in CM SAF ATBD [D1], Section 2.1.1.4 includes information on known limitations of the algorithm used to generate the SIS product and their implications.
The product description in CM SAF ATBD [D1], Section 2.2.1.3 includes information on known limitations of the algorithm used to generate the SDL product and their implications.
The product description in CM SAF ATBD [D1] Section 2.2.2.1 includes information on known limitations of the algorithm used to generate the SOL product and their implications.
CM SAF PUM [D2], Section 2.2 includes the general limitations on the application of the SIS, the SDL and the SOL products.
Known limitations of the algorithms and the general limitations apply to both TCDR and ICDR extensions of SOL and SDL
4.4 Disclaimer
The disclaimer outlined in CM SAF PUM [D2], Section 7 applies for all CM SAF brokered datasets.
Full licence text can be found in the Licence section of the landing page at the CDS-entry: Surface Radiation Budget derived from satellite observations https://cds.climate.copernicus.eu.
5. Data access information
The dataset is available in the C3S Climate Data Store (CDS, see Figure 1)
https://cds.climate.copernicus.eu/cdsapp#!/dataset/satellite-surface-radiation-budget?tab=overview
CLARA product family CDR is the part of the Surface Radiation Budget (SRB) Essential Climate Variable (ECV).
Figure 1: Copernicus CDS Landing Page.
5.1 Product ordering process
You need to be registered and logged in to order products in the CDS. A login is provided upon registration, all products in the CDS are delivered free of charge.
5.2 Visualization tool
The data may be visualized using the CDS Toolbox:
https://cds.climate.copernicus.eu/cdsapp#!/toolbox
References
References are listed in CM SAF ATBD [D1], Section 3, CM SAF Product User Manual [D2], Section 8 and CM SAF Validation Report [D3], Section 7.
