Contributors: G.E. Thomas (UKRI-STFC RAL Space), R.Shevchuk (Brockmann Consult)
Issued by: STFC RAL Space / Gareth Thomas and Brockmann Consult / Roman Shevchuk
Date: 29/07/2024
Ref: C3S2_D312a_Lot1.2.2.10_202407_PUGS_ECV_ERB_SLSTR_v1.2
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 |
Outgoing Longwave Radiation | OLR | Net total thermal radiation emitted by the Earth, as measured at the top of atmosphere. |
Reflected Solar Flux | RSF | Net total outgoing shortwave (UV, visible, near-IR) radiation at the top of atmosphere. This is dominated by reflected and scattered solar radiation. |
Table 2: Definition of various technical terms used in the document
Jargon | Definition |
TCDR | A Thematic Climate Data Record is a consistently processed time series of a geophysical variable. The time series should be 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. |
GCOS requirement | GCOS defines three requirements depending on user’s needs: - Goal (G): The strictest requirement, indicating no further improvements necessary - Breakthrough (B): Intermediate level between threshold and goal. Breakthrough indicates that it is recommended for certain climate monitoring activities - Threshold (T): Minimum requirement |
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. It is a platform that provides access to a wide range of climate data, including satellite and in-situ observations, reanalysis and other relevant datasets. |
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. |
Remapping | Interpolation of horizontal fields to a new, predefined grid. All datasets are remapped to the same grid (1°x1°, latitude from -90° to 90°, longitude from -180° to 180°) to make them comparable. The remap is done with bilateral interpolation. |
Collocation | A collocation consists in filtering nan values of different datasets in the same grid to make them uniform. This is necessary to compare e.g. the global average of two datasets. |
Cosine weighted averaging | Consideration of different grid box areas. Grid boxes on usual equal angle grid boxes have a different area depending on the latitude (with larger areas towards the equator). Towards the poles the same number of boxes covers a smaller area; therefore, a correction factor is needed to achieve equal area grid boxes. This factor is the cosine of the latitude. The method is applied for calculation of global averages. |
Table 3: 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. |
Scope of the document
This Product User Guide and Specification (PUGS) document is associated with the Climate Data Store (CDS) catalogue entry: Earth's radiation budget from 1979 to present derived from satellite observations. This Climate Data Record (CDR) comprises inputs from three 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 (also named TCDR (Thematic Climate Data Record)), and two Interim Climate Data Records (ICDR) extensions namely (ii) those produced under this contract for the CDS, specifically those coming from processing of the Sea and Land Surface Temperature Radiometers (SLSTR) by Rutherford Appleton Laboratory (RAL) Space and (iii) those produced under this contract for the CDS, specifically those coming from processing of the SLSTR by Brockmann Consult (BC).
Both of the ICDRs mentioned above are produced using the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm, using the Community Cloud for Climate (CC4CL) processor under the ESA Cloud_cci project. One ICDR was produced by Rutherford Appleton Laboratory (RAL) Space for the period 01/2017 to 06/2022 and the other ICDR by Brockmann Consult (BC) for the period 07/2022 to 12/2023.
This document provides information on how to use these products. It is not part of the official CCI documentation, but produced only 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 is generated 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 ICDR product was generated by RAL Space for the period from 01/2017 up to 06/2022 and by BC for the period 07/2022 to 12/2023.
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 TCDR 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. In addition to the individual data from each platform, a merged product is provided from 10/2018 onwards.
The TCDR and ICDRs provide level-3 data (monthly means) on two grids: (1) regular equal angle global latitude-longitude grid (2) regular equal area global latitude-longitude grid (the second option solely for the merged product from 07/2022 onwards). An overview of the various data producers, satellites, grids and time coverages for the ICDRs is shown in section 1, Figure 1-1.
Both grids have a resolution of 0.5°× 0.5° and includes these products: top-of-atmosphere Reflected Solar (shortwave) Flux (RSF) and Outgoing Longwave (thermal-IR) Radiation (OLR).
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 is provided; 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 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, versions 3.1.1 and 4.0 up to June 2022, are supplied to the CDS via the same route and uses the same processing software and infrastructure as the CDR. The SLSTR ICDR, version 4.0 for the period from 07/2022 to 12/2023 is processed on BC infrastructure using the same processing software for Level-2, the additional grid version (equal area) was processed using the Calvalus aggregator [D6] for the Level-3 step. 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 splits them into separate 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/. Detailed information on the cloud products and their use are outlined in the CCI Product User Guide [D3].
The product provides estimates of monthly mean global broadband top-of-atmosphere Earth radiation over land and ocean from the Along Track Scanning Radiometer ((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). All monthly means are provided on an equal angle projection. In addition, the product from 07/2022 onwards is provided on an equal area projection as well (see Figure 1-1 for an overview).
Figure 1-1:Overview of data producers, satellites, time coverages and grids for the ICDRs. Products above/below the horizontal black line are produced by RAL Space/Brockmann Consult (BC) respectively, while data from 07/2022 onwards is provided on two different grids.
1.1 Product description
The Cloud_cci product brokered to the CDS consists of top-of-atmosphere 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 this is described in the C3S ATBD [D1], Cloud_cci ATBD [D2], Cloud_cci CC4CL Broadband Radiative Flux Retrieval ATBD [D4], Sus et al. (2018) and McGarragh et al. (2018).
The brokered TCDR 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 TCDR.
1.2 Target requirements
The target requirements for ERB observations are laid-out in the Target Requirements and Gap Analysis Document [D5], and are summarized here. These requirements originate from 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 defines ideal targets that are often not attainable using existing or historical observing systems. Table 1-1 provides an overview of the GCOS targets 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:
\[ C3S-312bL1-L3C-MONTHLY-ERB-INST_ORAC_EA_PLATFORM_YYYYMM_fvV.V.nc, \]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), EA is added for the additional equal area grid and left out for the equal angle grid, and YYYYMM provides the year and month covered by the monthly mean product, and V.V denotes the product version.
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 available through the CDS.
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 v3.0 TCDR 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 https://climate.esa.int/en/data/#/dashboard, which provides online data mining, analysis and visualization tools for CCI data through the CCI Toolbox.
Only the(A)ATSR based TCDR is available through the ESA_cci data portal (original provider) as well as the CDS (brokered from CCI within the C3S Project), while SLSTR data is only supplied by the CDS.
2.2 Data access through the CDS
Within C3S, the distribution is through the CDS (https://cds.climate.copernicus.eu/) where documentation created for the inclusion of the data in the CDS, such as this PUGS, is also 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.
