Contributors: G. Thomas (STFC RAL Space)
Issued by: STFC RAL Space / Gareth Thomas
Date: 13/05/2021
Ref: C3S_D312b_Lot1.3.8.4-v3.3_202105_PUGS_CCIEarthRadiationBudget_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
Scope of the document
This document provides information on how to use the satellite-based estimates of Earth Radiation Budget produced by 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. 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. This document is not part of the official Cloud_cci documentation, but produced solely in the scope of the brokering to the CDS.
Executive summary
The ESA Climate Change Initiative (CCI) Earth Radiation Budget Climate Data Record (CDR) is a brokered product from the ESA Cloud_cci project, while the extension Interim CDR (ICDR) is produced from the Sea and Land Surface Temperature Radiometers (SLSTR) and is produced specifically for C3S. The product was generated by RAL Space, using the Community Cloud for Climate (CC4CL) processor, based on the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm. The Earth 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 SLSTR, beginning in 2017.
The CDR and ICDR provide level-3 data (monthly means) on a regular global latitude-longitude grid (with a resolution of 0.5°b× 0.5°) and includes these products: top-of-atmosphere reflected solar (shortwave) flux (RSF) and outgoing longwave (thermal-IR) radiation (OLR).
1. Cloud_cci global monthly Earth Radiation Budget products
The Cloud_cci global monthly Earth Radiation Budget product, version 3.0, is brokered to the CDS by the C3S from STFC RAL Space. The SLSTR ICDR, version 3.x, is supplied to the CDS via the same route and uses the same processing software and infrastructure as the TCDR. Although the format of the brokered data products differs from the official CCI products, the intellectual property rights remain with the Cloud_cci team. In detail, the official daily and monthly files from Cloud_cci contain more than 180 variables, but the specified C3S format split them into separated parts per ECV. That way, each file has a reduced data amount as well as an increased usability. 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 top-of-atmosphere Earth radiation over land and ocean from the Along Track Scanning Radiometer (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.
1.1 Product description
The Cloud_cci product brokered to the CDS consists of top-of-atmosphere radiation derived from the 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 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 Cloud_cci ATBD [D1], Cloud_cci CC4CL Broadband Radiative Flux Retrieval ATBD [D2], Sus et al. (2018) and McGarragh et al. (2018).
The brokered CDR is extended, with a five-year gap, from 2017 with an ICDR derived from the SLSTR instruments, which fly onboard the Copernicus operational Sentinel-3 satellites. From late 2018, a second Sentinel-3 platform is available, which doubles the spatial coverage of SLSTR and allows for nearly complete global coverage twice a day. The SLSTR product is produced using the same processing chain as the (A)ATSR CDR.
1.2 Target requirements
The target requirements for ERB observations are defined by the WMO Global Climate Observing System (GCOS) initiative, which defines and lays down targets for the observation of essential climate variables (ECVs). It should be noted that GCOS requirements are targets and are often not attainable using existing or historical observing systems. Table 1-1 provides an overview of the GCOS requirements for the ERB.
Table 1-1: GCOS targets for Earth 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 |
Top-of-atmosphere ERB longwave | olr |
|
Top-of-atmosphere ERB shortwave (reflected) | rsf |
|
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-ERB-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 TCDR, 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).
Data are provided as monthly means of Earth radiation values, 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 10:30 for ERS-2. Thus, the product does not contain any information on the diurnal variability of Earth radiation (due to changes in cloud cover and 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. The user is referred to the ATBDs [D1, D2] for details of the algorithms used in this process. In the case of SLSTR, daily coverage is significantly improved, with a single instrument covering over 1/2 the globe, while two instruments provide global coverage. SLSTR has the same local solar observation time as ENVISAT (10:00).
The list of Earth radiation properties, the variable names used within the NetCDF data files and their units are given in Table 1-2.
Table 1-2: Earth Radiation Budget variables included in Cloud_cci TCDR and SLSTR ICDR monthly products.
Property | Unit | Variable name |
Top-of-atmosphere reflected solar flux | Wm-2 | rsf |
Top-of-atmosphere outgoing longwave radiation | Wm-2 | olr |
2. Data access information
2.1 Data access through CCI
The original repository for the CCI formatted L3 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. In detail, the official daily and monthly files from Cloud_cci contain more than 180 variables, but the specified C3S format split them into separated parts per ECV. That way, each file has a reduced data amount as well as an increased usability. 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/cdsapp#!/dataset/satellite-earth-radiation-budget?tab=overview) 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.