Contributors: Oleksandr Bobryshev (DWD), A. C. Mikalsen (DWD)
Issued by: DWD/Bobryshev Oleksandr
Date: 09/06/2021
Ref: C3S_D312b_Lot1.2.2.2-v2.1_202007_PQAD_ECVSurfaceRadiationBudget_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 document is the Product Quality Assurance Document (PQAD) for CLARA Product family CDR. This document provides a brief guide to the data quality, and describes the validation method.
The brokered service within Copernicus solely refers to the CM SAF Validation Report [D1]. 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.
The longwave fluxes are not included in the CM SAF ICDR plans for the current phase. Therefore SOL and SDL change their license 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). Table 1 provides an overview of the licenses for all data CLARA family products.
All brokered CLARA data products (SIS, SOL, SDL) are validated against available reference data sets from surface measurements. The accuracy is defined based on the absolute bias derived from the validation with the reference data and evaluated against the accuracy requirements as given in the product requirements document [D5]. The accuracy estimation of SOL and SDL ICDR extensions is performed within the C3S using the algorithms developed by CM SAF.
An executive summary of the evaluation of the CLARA-A2.1 surface radiation dataset can be found in CM SAF Validation Report [D1], Section 1. An executive summary of the evaluation of the CLARA-based ICDR data record can be found in CM SAF Validation Report ICDR, Section 1 [D7].
An error budget (accuracy estimation and trend analysis) for the brokered radiation products can be found in CM SAF Validation Report [D1] Sections 5.2, 5.3 and 5.4 (for the TCDR); in CM SAF Validation Report, ICDR [D7] for ICDR SIS; in the PQAR [D6] for ICDR SOL and SDL. All data records fulfil the optimal or target accuracy requirements for the period 1992-2020, period when the ground based data are available (see PQAR [D6] for more details). The SDL and SOL datasets should not be used for validation of models, as these data are based on the ERA-reanalysis and model-derived data records (See [D1] Chapter 6).
The validation methodology for the extra data products is selected in a way to provide the most conservative accuracy estimation, i.e. by assuming that the uncertainties in the input datasets align perfectly and contribute fully to the overall uncertainty. The SRS accuracy is 7.8 (6.5) W/m2, the SNS accuracy is 13.0 (14.2) W/m2, the SNL accuracy is 21.9 (25.0) W/m2, and the SRB accuracy is 34.9 (39.2) W/m2, ICDR values are in parenthesis (see the PQAR [D6] for more details).
1. Validated products
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, 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 produced specifically within the C3S project as complimentary data for the convenience of users.
The CDR provided here (exclusively) 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 comprises two years of data 2019-2020.
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). 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). 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.
2. Description of validating datasets
The Surface Radiation CDR was validated against surface radiation measurements from the Baseline Surface Radiation Network (BSRN) (Ohmura et al., 1998). The reference dataset used for the validation is thoroughly described in CM SAF Validation Report [D1], Section 4.
At the time of writing (May 2021) only 34 out of 60 BSRN stations have submitted data for years 2019-2020. 12 stations had less than 4 month worth of data and they were discarded. The outgoing longwave measurements are performed not on all BSRN stations. Only 9 stations have submitted data for years 2019-2020 (see the PQAR [D6] for more details).
The accuracy of extra data products is derived based on the accuracy of the input data using the method of error propagation.
3. Description of product validation methodology
3.1 Validation methodology for SIS, SOL, SDL
The general validation methodology is fully described in CM SAF Validation Report, Section 5.1 [D1] and CM SAF Validation Report ICDR, Section 5.1 [D7]. Both TCDR and ICDR data are validated in the same way.
3.1.1 Surface Incoming Shortwave Radiation (SIS)
The validation of the SIS product is described in CM SAF Validation Report, Sections 5.2 [D1]. Validation of the ICDR part (2019-2020) is described in CM SAF Validation Report ICDR, Sections 5.2 [D7]
3.1.2 Surface Outgoing Longwave Radiation (SOL)
The validation of the SOL product is described in CM SAF Validation Report [D1], Section 5.3.
SOL is not included in the CM SAF ICDR plans for the current phase, so, for the ICDR dataset extension (2019 2020), SOL has been produced within the C3S contract. Validation methodology for the ICDR extension is same as TCDR.
3.1.3 Surface Downwelling Longwave Radiation (SDL)
The validation of the SDL product is described in CM SAF Validation Report [D1], Sections 5.4.
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. Validation methodology for the ICDR extension is same as TCDR.
3.2 Validation methodology for CLARA family extra data products
3.2.1 Surface Reflected Shortwave Radiation (SRS)
The accuracy of the SRS is determined based on the accuracy of the Surface Incoming Shortwave Radiation (SIS) from the Surface Radiation Budget brokered from EUMETSAT’s CM SAF CLARA-A2.1 dataset and the Surface Albedo (SAL), not provided within the C3S.
Estimates of the accuracy of the SIS product are given in CM SAF Validation Report [D1] and the accuracy of the SAL product is given in CM SAF Validation Report, Surface Albedo [D3].Applying the error propagation method, the accuracy of the SRS product can be estimated by:
\[ \Delta SRS=\frac{\delta SRS}{\delta SIS}\Delta SIS+\frac{\delta SRS}{\delta SAL}\Delta SAL=SAL\Delta SIS+SIS\Delta SAL \quad (Eq. 1) \]The accuracy for the SRS is calculated using the fixed accuracy values for the SIS ( \( \Delta SIS = 10 W/m^2 \) ) and the relative error of the SAL ( \( \Delta SAL = 25% \text{of the SAL value} \) ). These values are the target requirements for accuracy from the CM SAF Product Requirement Document [D5]. The resulting global mean accuracy for the SRS is 7.8 W/m2 for TCDR and 6.5 W/m2 for ICDR. Figure 1 provides the spatial distribution of the propagated SRS accuracies for TCDR and ICDR.
Figure 1: Spatial distribution of the propagated SRS accuracies for 1982-2018 (left) and 2019-2020 (right) years.
3.2.2 Surface Net Shortwave Radiation (SNS)
The accuracy of the SNS is determined based on the accuracy of the SIS and the SAL datasets.
Estimates of the accuracy of the SIS product are given in CM SAF Validation Report [D1] and the accuracy of the SAL product is given in CM SAF Validation Report, Surface Albedo [D3].
Applying the error propagation method, the accuracy of the SNS product can be estimated by:
\[ \Delta SNS=\frac{\delta SNS}{\delta SIS}\Delta SIS+\frac{\delta SNS}{\delta SAL}\Delta SAL= |(1-SAL)|\Delta SIS+|SIS|\Delta SAL \quad (Eq. 2) \]The accuracy for the SNS is calculated using the fixed accuracy values for the SIS ( \( \Delta SIS = 10 W/m^2 \) ) and the relative error of the SAL ( \( \Delta SAL = 25% \text{of the SAL value} \) ). These values are the target requirements for accuracy from CM SAF Product Requirement Document [D5]. Resulting global mean accuracy for the SNS is 13.0 W/m2 for TCDR and 14.2 W/m2 for ICDR. Figure 2 provides the spatial distribution of the propagated SNS accuracies for TCDR and ICDR.
Figure 2: Spatial distribution of the propagated SNS accuracies for 1982-2018 (left) and 2019-2020 (right) years.
3.2.3 Surface Net Longwave Radiation (SNL)
The accuracy of the SNL is defined by the accuracy of the Surface Downwelling Longwave Radiation (SDL) and the Surface Outgoing Longwave Radiation (SOL), both of which are part of the Surface Radiation Budget dataset brokered from EUMETSAT’s CM SAF CLARA-A2.1 [D4].
Estimations of the accuracy of the SDL and the SOL products are given in CM SAF Validation Report [D1]. Applying the error propagation method, the accuracy of the SNL product can be estimated by:
\[ \Delta SNL=\frac{\delta SNL}{\delta SDL}\Delta SDL+\frac{\delta SNL}{\delta SOL}\Delta SOL=\Delta SDL+\Delta SOL \quad (Eq. 3) \]The accuracy for the SNL is calculated using the fixed accuracy values for the SDL (
\( \Delta SDL=8.13 W/m^2 \)
) and the SOL (
\( \Delta SOL=13.77 W/m^2 \)
). Resulting global mean accuracy for the SNL is 21.9 W/m2.
Global mean accuracy for the SNL ICDR is 25.0 W/m2.
3.2.4 Surface Radiation Budget (SRB)
The accuracy of the SRB is defined by the accuracy of the SNS and the SNL datasets. Applying the error propagation method, the accuracy of the SNS product can be estimated by:
\[ \Delta SRB=\frac{\delta SRB}{\delta SNS}\Delta SNS+\frac{\delta SRB}{\delta SNL}\Delta SNL=\Delta SNS+\Delta SNL \quad (Eq. 4) \]The accuracy for the SRB is calculated using the fixed accuracy values for the SNS (
\( \Delta SNS=13.0 W/m^2 \)
and the SNL (
\( \Delta SNL=21.9 W/m^2 \)
). Resulting global mean accuracy for the SRB is 34.9 W/m2.
Global mean accuracy for the SNL ICDR is 39.2 W/m2.
4. Summary of validation results
A summary of the validation results is provided in CM SAF Validation Report Section 6 [D1], CM SAF Validation Report ICDR Section 6 [D7] and C3S PQAR Document [D6].
The validation methodology for the extra data products is selected in a way to provide the most conservative accuracy estimation, i.e. by assuming that the uncertainties in the input datasets align perfectly and contribute fully to the overall uncertainty. The SRS accuracy is 7.8 (6.5) W/m2, the SNS accuracy is 13.0 (14.2) W/m2, the SNL accuracy is 21.9 (25.0) W/m2, and the SRB accuracy is 34.9 (39.2) W/m2, ICDR values are in parenthesis.
References
References are listed in CM SAF Validation Report Surface Radiation Products [D1], Section 7 and in CM SAF Validation Report Surface Albedo [D3], Section 6.
Ohmura, A., et al. (1998), Baseline Surface Radiation Network (BSRN/WCRP): New precision radiometry for climate research, Bulletin of the American Meteorological Society, 79(10), 2115-2136.
