Contributors: G.E. Thomas (UKRI-STFC RAL Space)
Issued by: STFC RAL Space (UKRI-STFC) / Gareth Thomas
Date: 06/03/2023
Ref: C3S2_D312a_Lot1.2.3.4-v4.0_202303_PUGS_CCISurfaceRadiationBudget_v1.1
Official reference number service contract: 2021/C3S2_312a_Lot1_DWD/SC1
History of modifications
List of datasets covered by this document
Related documents
Acronyms
List of tables
List of figures
General definitions
Table 1: Summary of variables and definitions
Variables | Abbreviation | Definition |
Surface incoming solar radiation | SIS | Total incoming shortwave (UV, visible, near-IR) radiation, measured at the Earth’s surface. |
Surface reflected solar radiation | SRS | Total upwelling shortwave radiation, measured at the Earth’s surface. |
Surface net solar radiation | SNS | The net shortwave radiation, measured at the Earth’s surface. Equal to the difference between SIS and SRS. |
Surface downwelling longwave radiation | SDL | Total downwelling thermal radiation, measured at the Earth’s surface. |
Surface outgoing longwave radiation | SOL | Total upwelling thermal radiation, measured at the Earth’s surface. |
Surface net longwave radiation | SNL | The net longwave radiation, measured at the Earth’s surface. Equal to the difference between SDL and SOL. |
Surface radiation budget | SRB | The total net radiative flux (both short- and longwave) at the Earth’s surface. Equal to the total of SNS and SNL. |
Table 2: Definition of processing levels
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
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 Product User Guide and Specification (PUGS) document is associated with the Climate Data Store (CDS) catalogue entry: Surface radiation budget from 1982 to present derived from satellite observations. This Climate Data Record (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 CDS, specifically those coming from processing of the Sea and Land Surface Temperature Radiometers (SLSTR). Both CDRs are produced by Rutherford Appleton Laboratory (RAL) Space using the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm, using the Community Cloud for Climate (CC4CL) processor under the ESA Cloud_cci project. This document provides information on how to use these products and it is not part of the official CCI documentation, but produced only in the scope of the brokering to the CDS. Therefore, this document referes to several Cloud_cci documents (see Related documents), namely the ESA Cloud_cci ATBD [D2], the ESA Cloud_cci Product User Guide (PUG) [D3], and the ESA Cloud_cci Error characterization report [D4], with additional information specific to SLSTR included.
Executive summary
The ESA Climate Change Initiative (CCI) Surface Radiation Budget Climate Data Record (CDR) is a brokered product from the ESA Cloud_cci project, while the extension Interim CDR (ICDR) produced from the Sea and Land Surface Temperature Radiometers (SLSTR) is produced specifically for C3S. The product is generated by RAL Space, using the Community Cloud for Climate (CC4CL) processor, based on the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm. The Surface Radiation Budget is a product of the Broadband Radiative Flux Retrieval (BRFR) module of CC4CL, which uses the cloud properties produced by ORAC to compute broadband radiative flux values.
The Cloud_cci dataset comprises 17 years (1995-2012) of satellite-based measurements derived from the Along Track Scanning Radiometers (ATSR-2 and AATSR) onboard the ESA second European Research Satellite (ERS-2) and ENVISAT. This CDR is partnered with the ICDR produced from the Sentinel-3 Sea and Land Surface Temperature Radiometers (SLSTR), beginning in 2017 (Sentinel-3A) and 2018 (Sentinel-3B), when data from each platform became available.
The dataset encompasses level-3 data (monthly means) on a regular global latitude-longitude grid (with a resolution of 0.5°× 0.5°) and includes these products: the Surface Incoming and Reflected Shortwave radiation (SIS and SRS respectively), the Surface Downwelling and Outgoing Longwave radiation (SDL and SOL respectively), the Surface Net Shortwave and Longwave radiation (SNS and SNL), and the total Surface Radiation Budget (SRB).
These products are brokered to (in the case of (A)ATSR) or produced for the Climate Data Store (in the case of SLSTR) by the Copernicus Climate Change Services (C3S). The respective data products (monthly means) are first described in terms of their input data and a brief overview of the algorithms; their target requirements in the scope of C3S and achieved performances are given; relevant information for usage is provided. The latter comprises geographical grid specifications, the data format, naming conventions, and the acknowledgement policy.
1. Cloud_cci global monthly surface radiation budget products
The Cloud_cci global monthly Surface Radiation Budget CDR, version 3.0, is brokered to the CDS by the C3S from STFC RAL Space. The SLSTR ICDR, versions 3.1.1 and 4.0, are supplied to the CDS via the same route and uses the same processing software and infrastructure as the CDR. Although the format of the brokered data products differs from the official CCI products, the intellectual property rights remain with the Cloud_cci team. The landing page for the official CCI products is https://climate.esa.int/en/projects/cloud/.
The product provides estimates of monthly mean global broadband surface radiation over land and ocean from (A)ATSR series of satellite sensors, on a 0.5°×0.5° latitude-longitude grid from mid-1995 until early 2012. The SLSTR based ICDR extends the coverage, with a five-year gap, from 2017 onwards and is only available through the CDS. Version 3.1.1 of the ICDR provides data from a single SLSTR (flying on board either Sentinel-3a or -3b), while version 4.0 combines data from both SLSTR instruments into a single combined product (starting with the launch of the Sentinel-3b in late 2018). The processing of version 3.1.1 and 4.0 are identical – the sole difference is whether the two instruments are separately or treated as a single data-stream.
1.1 Product description
The Cloud_cci product brokered to the CDS consists of surface radiation derived from the (A)ATSR instruments; specifically:
- ATSR-2, which flew on the second European Research Satellite (ERS-2) from June 1995 until January 2008. ERS-2 lost global coverage in June 2003, due to failure of the onboard data storage; Cloud_cci data do not extent beyond this date (thus providing approximately one-year of overlap with the succeeding AATSR product).
- Advanced-ATSR (AATSR), which flew on ENVISAT from May 2002 until the satellite’s failure in April 2012.
When referred to in terms of a continuous data record, these two instruments are commonly described as (A)ATSR. The preceding ATSR-1 instrument lacked the visible-NIR channels provided by (A)ATSR and thus isn’t included in the Cloud_cci product.
The Cloud_cci also produced cloud and radiation products from the Advanced Very High Resolution Radiometer (AVHRR) series of instruments and the Moderate Resolution Imaging Spectroradiometer (MODIS), using a common retrieval technique, but only the (A)ATSR products are brokered to the CDS.
The ICDR consists of the same essential climate variables (ECVs) derived from the SLSTR instruments flying on board the Sentinel-3A (from 2017 onwards) and Sentinel-3B (from 2018 onwards).
The analysis algorithm applied in producing the Cloud_cci products is the Optimal Retrieval of Aerosol and Clouds (ORAC), with broadband flux calculations performed using the BUGSRad radiative transfer code (Stephens et al., 2001). The overall data processing system used in the project is referred to as Community Cloud for Climate (CC4CL), and these are detailed in the C3S ATBD [D1], Cloud_cci ATBD [D2], Cloud_cci CC4CL Broadband Radiative Flux Retrieval ATBD [D3], Sus et al. (2018) and McGarragh et al. (2018).
1.2 Target requirements
The target requirements for SRB observations are laid-out in the Target Requirements and Gap Analysis Document [D5], but are summarised here. These requirements originate from the WMO Global Climate Observing System (GCOS) initiative, which defines and lays down targets for the observation of ECVs. It should be noted that GCOS requirements are targets for what should be achievable through Earth observation and are often not attainable using existing or historical observing systems. Table 1-1 provides an overview of the GCOS requirements for the surface radiative balance.
Table 1-1: GCOS targets for surface radiation budget ECVs. Note that the Cloud_cci doesn't meet the requirement for resolving the diurnal cycle due to the nature of the satellite observations, but exceeds the spatial resolution and aims to achieve the uncertainty and stability requirements.
Quantity | Cloud_cci variable | Targets |
Surface ERB longwave | snl |
|
Surface ERB shortwave | sns |
|
1.3 Data usage information
Cloud_cci products are provided in NetCDF (version 4), which are compliant with the conventions CF 1.8 and the NASA Global Change Master Directory (GCMD) Science Keywords vocabulary. Filenames follow the structure:
C3S-312bL1-L3C-MONTHLY-SRB-INST_ORAC_PLATFORM_YYYYMM_fvVVV.nc,
where INST and PLATFORM refer to the instrument and platform from which data originates (either ATSR2 and ERS2, or AATSR and ENVISAT for the CDR, or SLSTR and Sentinel-3a or -3b for the ICDR), YYYYMM provides the year and month covered by the monthly mean product, and VVV denotes the product version (3.0 for the TCDR, 3.1 for the ICDR).
The list of surface radiation properties, the variable names used within the NetCDF data files and their units are given in Table 1-2.
Data are provided as monthly means of surface radiation properties, on a regular latitude-longitude grid, with a spacing of 0.5° in both dimensions (thus grid centres lie at -89.75°, -89.25°, -88.75°, …, 89.75° in latitude and -179.75°, -179.25°, -178.75°, …, 179.75° in longitude).
These values are monthly averages of estimated daily mean radiative fluxes, derived from satellite observations made at a fixed local solar time of 10:00 for ENVISAT and both Sentinel-3s, and 10:30 for ERS-2. Thus, the product does not contain any information on the diurnal variability of surface radiation (due to changes in cloud cover and cloud properties for example). Furthermore, the narrow swath of the (A)ATSR instruments means that only approximately 1/3 of the globe is covered each day, whereas the SLSTR based products provide almost global daily coverage. The user is referred to the ATBDs [D1, D2, D3] for details of the algorithms used in this process.
Table 1-2: Surface Radiation Budget variables included in Cloud_cci TCDR and SLSTR ICDR monthly products.
Property | Unit | Variable name | Comment |
Surface incoming solar radiation | Wm-2 | sis | |
Surface reflected solar radiation | Wm-2 | srs | |
Surface net solar radiation | Wm-2 | sns | Equivalent to "Surface ERB shortwave" GCOS ECV and calculated as sns = sis – srs. |
Surface downwelling longwave radiation | Wm-2 | sdl | |
Surface outgoing longwave radiation | Wm-2 | sol | |
Surface net longwave radiation | Wm-2 | snl | Equivalent to "Surface ERB longwave" GCOS ECV and calculated as snl = sdl – sol. |
Total surface radiation budget | Wm-2 | srb | Calculated as srb = (sis + sdl) - (srs + sol). |
2. Data access information
2.1 Data access through CCI
The original repository for the CCI formatted L3 v3.0 CDR data can be accessed through the Cloud_cci homepage https://climate.esa.int/en/projects/cloud/data/, as can all relevant documentation from the project. It should be noted that Cloud_cci L3 data is not in the same format as data brokered to the CDS, however the same L2 retrieval output was used to produce both products.
Cloud_cci data should also be available through the ESA CCI data portal http://cci.esa.int/data, which provides online data mining, analysis and visualization tools for CCI data through the CCI Toolbox.
Only the brokered (A)ATSR based CDR is available through CCI, with SLSTR data being supplied only to the CDS.
2.2 Data access through the CDS
Within C3S, the distribution will be through the CDS (https://cds.climate.copernicus.eu/) where documentation created for the inclusion of the data in the CDS, such as this PUGS, will also be provided.
2.3 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.
References
McGarragh, G., C.A. Poulsen, G.E. Thomas, A.C. Povey, O. Sus, S. Stapelberg, C. Schlundt, S. Proud, M.W. Christensen, M. Stengel, R. Hollmann, R.G. Grainger, 2018: The Community Cloud retrieval for Climate (CC4Cl) – Part 2: The optimal estimation approach. Atmos. Meas. Tech., 11. 3397-3431, DOI: 10.5194/amt-11-3397-2018.
Stephens, G.L., P.M. Gabriel, P.T. Partain, 2001: Parameterization of atmospheric radiative transfer. Part I: Validity of simple models. J. Atmos. Sci., 58, 3391-3409, DOI: 10.1175/1520-0469(2001)058<3391:POARTP>2.0.CO;2.
Sus, O., M. Stengel, S. Stapelberg, G. McGarragh, C.A. Poulsen, A.C. Povey, C. Schlundt, G.E. Thomas, M. Christensen, S. Proud, M. Jerg, R.G. Grainger, R. Hollmann, 2018: The Community Cloud retrieval for Climate (CC4Cl) – Part 1: A framework applied to multiple satellite imaging sensors. Atmos. Meas. Tech., 11, 3373-3396, DOI: 10.5194/amt-11-3373-2018.
