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Acronyms
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Acronyms
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Table 1-1: Summary of methodologies used to estimate the accuracies, for TCDR and ICDR datasets. Table 2-1: Summary of the accuracy of the Surface Radiation Budget dataset. Table 43-1: Summary of KPI results with 2.5 and 97.5 percentiles and number of ICDR months within the range Table 4-1: GCOS targets for Earth GCOS targets for Surface Radiation Budget ECVs and TCDR CDR values. |
List of figures
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Figure 2-1: Results from [D1]; Top: Validation results for Cloud_cci surface incoming shortwave (SIS) flux using BSRN as a reference. Bottom: Bias for each ground station. Figure 2-2: Results from [D1]; Top: Validation results for Cloud_cci surface downwelling longwave (SDL) flux using BSRN as a reference. Bottom: Bias for each ground station. Figure 2-3: SRS, SOL, SIS and SDL values from SLSTR (ICDR dataset) for March 2017. Figure 2-4: SRS, SOL, SIS and SDL values from CERES dataset for March 2017. |
General definitions
The “CCI product family” Climate Data Record (CDR) consists of two parts. The ATSR2-AATSR Surface Radiation Budget CDR is formed by a TCDR brokered from the ESA Cloud_cci project and an ICDR derived from the Sea and Land Surface Temperature Radiometer (SLSTR) on board of Sentinel-3A and -B. ICDR uses the same processing and infrastructure as the TCDR. Both TCDR and ICDR data have been produced by STFC RAL Space.
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Stability: The variation of the bias over a multi-annual time period
Table 1: Summary of variables and definitions Anchor table1 table1
Variables | Abbreviation | Definition |
Surface incoming solar radiation | SIS | The total incoming solar flux, measured at the Earth’s surface. |
Surface reflected solar radiation | SRS | The total upwelling shortwave flux, measured at the Earth’s surface. |
Surface net solar radiation | SNS | The net downwelling solar flux, measured at the surface (equal to SIS – SRS). |
Surface downwelling longwave radiation | SDL
| The total downwelling thermal infrared flux, measured at the Earth’s surface. |
Surface outgoing longwave radiation
| SOL
| The total upwelling thermal infrared flux, measured at the Earth’s surface. |
Surface net longwave radiation | SNL | The net downwelling thermal infrared flux, measured at the Earth’s surface (equal to SDL-SOL). |
Total surface radiation budget | SRB | The total net downwelling radiative flux, measured at the Earth’s surface (equal to (SIS+SDL) – (SRS+SOL)). |
Table 2: Definition of processing levels Anchor table2 table2
Processing level | Definition |
Level-1b | The full-resolution geolocated radiometric measurements (for each view and each channel), rebinned onto a regular spatial grid. |
Level-2 (L2) | Retrieved cloud variables at full input data resolution, thus with the same resolution and location as the sensor measurements (Level-1b). |
Level-3C (L3C) | Cloud properties of Level-2 orbits of one single sensor combined (averaged) on a global spatial grid. Both daily and monthly products provided through C3S are Level-3C. |
Table 3: Definition of various technical terms used in the document Anchor table3 table3
Jargon | Definition |
Brokered product | The C3S Climate Data Store (CDS) provides both data produced specifically for C3S and so-called brokered products. The latter are existing products produced under an independent programme or project which are made available through the CDS. |
Climate Data Store (CDS) | The front-end and delivery mechanism for data made available through C3S. |
Retrieval | A numerical data analysis scheme which uses some form of mathematical inversion to derive physical properties from some form of measurement. In this case, the derivation of cloud properties from satellite measured radiances. |
Forward model | A deterministic model which predicts the measurements made of a system, given its physical properties. The forward model is the function which is mathematically inverted by a retrieval scheme. In this case, the forward model predicts the radiances measured by a satellite instrument as a function of atmospheric and surface state, and cloud properties. |
TCDR | It is a consistently-processed time series of a geophysical variable of sufficient length and quality. |
ICDR | An Interim Climate Data Record (ICDR) denotes an extension of TCDR, processed with a processing system as consistent as possible to the generation of TCDR. |
CDR | A Climate Data Record (CDR) is defined as a time series of measurements with sufficient length, consistency, and continuity to determine climate variability and change. |
Scope of the document
This document provides a description of the product validation results for the Climate Data Record (CDR) of the Essential Climate Variable (ECV) Surface Radiation Budget. This CDR comprises inputs from two sources: (i) brokered products from the Cloud Climate Change Initiative (ESA’s Cloud_cci), namely those coming from processing of the Advanced Along-Track Scanning Radiometer (A)ATSR) data and (ii) those produced under this contract for the Climate Data Store, specifically those coming from processing of the Sea and Land Surface Temperature Radiometers (SLSTR).
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Table 1-1: Summary of methodologies used to estimate the accuracies, for TCDR and ICDR datasets. Anchor table1_1 table1_1
Product name | Validation with BSRN | Comparison with CERES | Uncertainty propagation |
Surface Incoming Shortwave radiation (SIS) | TCDR | TCDR and ICDR |
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Surface Reflected Shortwave radiation (SRS) |
| TCDR and ICDR | TCDR and ICDR |
Surface Net Shortwave radiation (SNS) |
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| TCDR and ICDR |
Surface Outgoing Longwave radiation (SOL) |
| TCDR and ICDR |
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Surface Downwelling Longwave radiation (SDL) | TCDR | TCDR and ICDR |
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Surface Net Longwave radiation (SNL) | TCDR and ICDR | ||
Surface Radiation Budget (SRB) |
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| TCDR and ICDR |
The Product Validation and Intercomparison Report [D1] includes the validation and intercomparison of the TCDR Surface Radiation Budget versus the CERES satellite dataset. The same methodology is used for the ICDR.
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1 Please find more information on the reference data on [D1]: BSRN (Annex A.5) and CERES (A.6) |
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The validation results for the TCDR products are presented and described in detail in [D1], sections 3.3.2, 5.3 and 5.4. In this document, a summary highlighting the main results is presented. Only SIS and SDL in the TCDR product are validated with BSRN. All All other properties (including SIS and SDL in the ICDR) are compared with CERES. The evaluation with CERES is considered to be a comparison because the CERES surface radiation dataset has a similar accuracy to the CDR dataset.
Table 2-1: Summary of the accuracy of the Surface Radiation Budget dataset. The ‘bold’ accuracies come from direct validation with a ground measurement network (BSRN), the others come from the intercomparison with similar datasets (CERES) or with an uncertainty propagation. ICDR values are obtained from data between January 2017 and December 2021 for SLSTR-A and between October 2018 and December 2021 for SLSTR-B. Anchor table2_1 table2_1
Product name | TCDR Accuracy [W/m2] | ICDR SLSTR-A Accuracy [W/m2] | ICDR SLSTR-B Accuracy [W/m2] | ICDR A+B Accuracy [W/m2] |
Surface Incoming Shortwave radiation (SIS) | 8.2 | 1.8 | 0.23 | 0.51 |
Surface Reflected Shortwave radiation (SRS) | 4.6 | 1.6 | 2.1 | 2.2 |
Surface Net Shortwave radiation (SNS) | 13 | 3.4 | 2.3 | 2.7 |
Surface Outgoing Longwave radiation (SOL) | 11 | 1.6 | 4.1 | 3.8 |
Surface Downwelling Longwave radiation (SDL) | 12 | 9.7 | 11 | 11 |
Surface Net Longwave radiation (SNL) | 23 | 11 | 15 | 15 |
Surface Radiation Budget (SRB) | 36 | 14 | 17 | 18 |
The ICDR data of SIS, SRS, SOL and SDL are compared with CERES, using the methodology described in [D1] section 5.3 and 5.4, and results are presented here in section 2.2.
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The resulting global mean accuracy for the SRB is 36 W/m2 for TCDR, 14 W/m2 , 17 W/m2 and 18 W/m2 for ICDR SLSTR-A , B and A+B respectively.
3. Application(s)
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specific assessments
In addition to the extensive product validation (see chapter 2 for results and chapter 2/3 in [D6] for validation methodology) a second assessment is introduced to evaluate the Interim Climate Data Record (ICDR) against the Thematic Climate Data Record (TCDR) in terms of consistency. Since frequent ICDR deliveries make detailed validation not feasible, a consistency check against the deeply validated TCDR is used as an indication of quality. This is done by a comparison of the following two evaluations:
- TCDR against a stable, long-term and independent reference dataset
- ICDR against the same stable, long-term and independent reference dataset
The evaluation method is generated to detect differences in the ICDR performance in a quantitative, binary way with so called Key Performance Indicators. The general method is outlined in [D5] chapter 3. The same difference between TCDR/ICDR and the reference dataset would lead to the conclusion that TCDR and ICDR have the same quality (key performance is "good"). Variations or trends in the differences (TCDR/ICDR against reference) would require a further investigation to analyze the reasons. The key performance would be marked as "bad". The binary decision whether the key performance is good or bad is made in a statistical way by a hypotheses test (binomial test). Based on the TCDR/reference comparison (global means, monthly or daily means) a range is defined with 95% of the differences are within. This range (2.5 and 97.5 percentile) is used for the ICDR/reference comparison to check whether the values are in or out of the range. The results could be the following:
- All or a sufficient high number of ICDR/reference differences lies within the range defined by the TCDR/reference comparison: Key performance of the ICDR is "good"
- A smaller number of ICDR/reference differences is within the pre-defined range: Key performance of the ICDR is "bad"
3.1 Results
The results of the KPI test are summarized in Table 3-1.
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Surface Incoming Shortwave Radiation | Surface Reflected Shortwave Radiation | Surface Outgoing Longwave Radiation | Surface Downwelling Longwave Radiation | ||
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Percentiles | p2.5 p97.5 | -1.29 W/m² 2.12 W/m² | -0.45 W/m² 0.36 W/m² | -16.4 W/m² 11.3 W/m² | -4.65 W/m² 4.48 W/m² |
Sentinel-3A: | |||||
01/2017 - 12/2020 | 11/37 | 08/37 | 00/37 | 35/37 | |
01/2017 - 12/2021 | 44/60 | 48/60 | 60/60 | 15/60 | |
01/2017 - 06/2022 | 44/63 | 51/63 | 63/63 | 15/63 | |
Sentinel-3B: | |||||
10/2018 - 12/2021 | 24/39 | 29/39 | 39/39 | 10/39 | |
10/2018 - 06/2022 | 25/42 | 32/42 | 42/42 | 10/42 | |
Sentinel-3A+B: | |||||
10/2018 - 06/2022 | 36/42 | 32/42 | 42/42 | 20/42 |
Percentiles were calculated based on the comparison of the TCDR using the Advanced Along Track Scanning Radiometer (AATSR) instrument against CERES as reference dataset for the variables Surface Incoming Shortwave Radiation (SIS), Surface Reflected Shortwave Radiation (SRS), Surface Outgoing Longwave Radiation (SOL) and Surface Downwelling Longwave Radiation (SDL). Percentiles were based on the time from 2002-2012 with monthly means and applied to the ICDR from 01/2017 (10/2018) to 06/2022 for Sentinel-3A (Sentinel-3B and merged product Sentinel-3A+B) based on measurements of the Sea and Land Surface Temperature Radiometer (SLSTR).
Most of the ICDR months are outside the TCDR-based KPI limits and leading to “bad” KPI tests. Therefore, the ICDR is not stable in relation to the TCDR. This is due to multiple reasons starting with the fact of a five year gap (2012-2016) between TCDR and ICDR. In addition, TCDR and ICDR are based on different instruments with SLSTR on Sentinel-3 and (A)ATSR/ATSR-2 on Envisat/ERS-2, respectively. Differences occur due to a lower bias between ICDR and reference dataset and a subtraction of the monthly means (based on the TCDR) to remove the annual cycle leads to values outside of the KPI range (see method in [D5], chapter 3.2.2). Please note that significant changes between 01/2017 - 12/2020 and 01/2017 - 12/2021 are due to bugfixesThis section is not applicable. There are no additional application specific assessments known since the dataset has just been published.
4. Compliance with user requirements
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Table 4-1: GCOS targets for Earth Radiation Budget ECVs and CDR values. TCDR values taken from Table 5-4 and Table 5-5 in [D1]. Anchor table4_1 table4_1
Product name |
| GCOS targets | Cloud_cci dataset |
SIS | Frequency | Monthly (resolving diurnal cycles) | Cloud_cci products do not meet the requirement for resolving the diurnal cycle. |
Resolution | 100 km | Cloud_cci products exceed the spatial resolution. | |
Measurement uncertainty | 1 W/m² on global mean | Uncertainty: 8.2 W/m² Standard Deviation: 24 W/m² on global mean (Validation with BSRN ground base measurements) | |
Stability | 0.2 W/m²/decade | 0.97 W/m²/decade (Comparison with CERES) | |
SDL | Frequency | Monthly (resolving diurnal cycles) | Cloud_cci products do not meet the requirement for resolving the diurnal cycle. |
Resolution | 100 km | Cloud_cci products exceed the spatial resolution. | |
Measurement uncertainty | 1 W/m² on global mean | Uncertainty: 12 W/m2 Standard Deviation: 15 W/m2 on global mean (Validation with BSRN ground base measurements) | |
Stability | 0.2 W/m²/decade | 2.76 W/m2/decade (Comparison with CERES) |
Known limitations [From D1 table 7.1]:
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This document has been produced with funding by the European Union in the context of the Copernicus Climate Change Service (C3S) .The activities leading to these results have been contracted, operated by the European Centre for Medium-Range Weather Forecasts , operator of C3Son behalf ofon the European Union ( Delegation Agreement signed on 11/11/2014 andContribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee orof warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt, the European Commission and the European Centre for Medium-Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view. |
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