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Contributors: G.E. Thomas(UKRI-STFC RAL Space)

Issued by: RAL Space (UKRI-STFC)

Date: 16/11/2020

Ref: C3S_D312b_Lot1.1.5.4-v3.1_202011_ATBD_CCIEarthRadiationBudget_v1.0

Official reference number service contract: 2018/C3S_312b_Lot1_DWD/SC1

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History of modifications

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Version Date Description of modification Chapters/Sections V1.0 04/11/2020 Initial All

List of datasets covered by this document

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Deliverable ID Product title Product type (CDR, ICDR) Version number Delivery date D3.3.25-v3.0 ECV Earth Radiation Budget brokered from ESA's Cloud_cci ATSR-AATSRv3 dataset CDR V3.0 22/07/2020 D3.3.26-v3.x ECV Earth Radiation Budget derived from SLSTR ICDR V3.1 30/11/2020 – onward

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Related documents

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Reference ID Document D1 Algorithm Theoretical Basis Document, v.6.2. ESA Cloud_cci. https://climate.esa.int/media/documents/Cloud_Algorithm-Theoretical-Baseline-Document-ATBD_v6.2.pdf Last accessed on 11/10/2022 D2 Product User Guide, v5.1. ESA Cloud_cci. https://climate.esa.int/media/documents/Cloud_Product-User-Guide-PUG_v5.1.pdf Last accessed on 11/10/2022 D3 Algorithm Theoretical Basis Document, CC4CL, v6.2. ESA Cloud_cci. https://climate.esa.int/media/documents/Cloud_Algorithm-Theoretical-Baseline-Document-ATBD-CC4CL_v6.2.pdf Last accessed on 11/10/2022 D4 Comprehensive Error Characterization Report, v.4.1. ESA Cloud_cci. https://climate.esa.int/media/documents/Cloud_Comprehensive-Error-Characterisation-Report-CECR_v4.1.pdf Last accessed on 11/10/2022 D5 Algorithm Theoretical Basis Document: CC4Cl Broadband Radiative Flux Retrieval, v1.1. ESA Cloud_cci. https://climate.esa.int/media/documents/Cloud_Algorithm-Theoretical-Baseline-Document-ATBD-CC4CL-TOAFLUX_v1.1.pdf Last accessed on 11/10/2022 D6 Algorithm Theoretical Basis Document (AATSR Oxford-RAL Aerosol and Cloud), Version 3.0. ESA Aerosol_cci. http://cci.esa.int/sites/default/files/Aerosol_cci2_ATBD_ATSR_ORAC_v3.0.pdf Last accessed on 11/10/2022 D7 Sus et al. The Community Cloud retrieval for Climate (CC4CL). Part I: A framework applied to multiple satellite imaging sensors, Atmos. Meas. Tech. 2017. DOI: https://doi.org/10.5194/amt-2017-334 D8 McGarragh et al. The Community Cloud retrieval for CLimate (CC4CL). Part II: The optimal estimation approach, Atmos. Meas. Tech. 2017. DOI: https://doi.org/10.5194/amt-2017-333 D9 AATSR Detailed Processing Model Level 1b. Ref: PO-TN-RALS-GS-10004. http://cci.esa.int/sites/default/files/Aerosol_cci2_ATBD_ATSR_ORAC_v3.0.pdf Last accessed on 15/10/2019 D10 ENVISAT-style products for ATSR-1 and ATSR-2 data. Ref: APP-TN-005. https://earth.esa.int/c/document_library/get_file?folderId=46990&name=DLFE-694.pdf  Last accessed on 15/10/2019 D11 Sentinel-3 SLSTR Technical Guide. https://sentinel.esa.int/web/sentinel/technical-guides/sentinel-3-slstr/instrument Last accessed on 23/09/2020

Acronyms

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Acronym Definition AATSR Advanced Along-Track Scanning Radiometer ATBD Algorithm Theoretical Basis Document ATSR-1, -2 Along Track Scanning Radiometer AVHRR Advanced Very High Resolution Radiometer BRDF Bidirectional Reflection Distribution Function BRFR Broadband Radiative Flux Retrieval C3S Copernicus Climate Change Service CC4CL Community Cloud retrieval for Climate CCI (ESA) Climate Change Initiative CDR Climate Data Record CDS Climate Data Store DARD Data Access Requirements Document ECMWF European Centre for Medium Range Weather Forecasts ECV Essential Climate Variable ENVISAT (the) Environmental Satellite ERA ECMWF Re-Analysis ERB Earth Radiation Budget ERS-2 Environmental Research Satellite ESA European Space Agency FCDR Fundamental Climate Data Record GCMD Global Change Master Directory ICDR Interim Climate Data Record IR InfraRed MODIS Moderate Resolution Imaging Spectroradiometer MWIR Mid-Wavelength InfraRed NEΔT Noise-Equivalent delta-Temperature ORAC Optimal Retrieval of Aerosol and Cloud PUG Product User Guide RAL Rutherford Appleton Laboratory RITS Radiative Important Trace Species RTTOV Radiative Transfer for TOVS (TIROS Observational Vertical Sounder) SLSTR Sea and Land Surface Temperature Radiometer SOHO Solar and Heliospheric Observatory SORCE SOlar Radiation and Climate Experiment STFC Science and Technology Facilities Council SWIR Short-Wavelength InfraRed TIR Thermal InfraRed TIROS Television and Infra-Red Observation Satellite UKRI UK Research and Innovation VIS Visible (wavelengths)

Scope of the document

This Algorithm Theoretical Basis Document (ATBD) describes the generation of the Climate Data Record (CDR) on Earth Radiation Budget, which is a brokered service from ESA’s Cloud_cci, and its extension with an interim-CDR (ICDR) derived from the Sea and Land Surface Temperature Radiometer (SLSTR) on the Sentinel-3 platform. This extension of the ESA Cloud_cci dataset is generated specifically for C3S by RAL Space, but is derived using the same algorithm and processing chain. Therefore, this document refers to several Cloud_cci documents (see Related documents), namely the Cloud_cci ATBD [D1], the Broadband Radiative Flux Retrieval ATBD [D5] and the ESA Cloud_cci Product User Guide (PUG) [D2]. These documents describe the data processing chain and the algorithms used to generate the Earth radiation products and the cloud products on which they are based. The assessment described in this document is carried out within the scope of C3S, whereas the intellectual property rights of the products themselves remain with the Cloud_cci, in the case of the CDR, or lie with STFC RAL Space, in the case of the ICDR. 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 CDR on Earth Radiation Budget is a brokered product of the CC4CL dataset produced by ESA's Cloud_cci project, and the SLSTR ICDR is an extension to the brokered product. Accordingly, this document largely refers to the ESA Cloud_cci documentation, with additional information specific to SLSTR included.

The Cloud_cci record comprises 17 years (1995-2012) of satellite-borne observations derived from measurements of the ATSR series of satellites on board the ESA ERS-2 and ENVISAT satellites. The CDR provided here comprises monthly means (0.5° x 0.5° resolution) of Earth radiation on a regular global latitude-longitude grid. The SLSTR ICDR continues this record, with a 5-year gap, with version v3.x providing cloud and radiation budget products from SLSTR from 2017 on.

The Earth Radiation Budget products are top-of-atmosphere reflected solar (shortwave) flux and outgoing longwave (thermal-IR) radiation. Note that the brokered service within Copernicus provides only a subset of the original CCI cloud properties and radiation dataset, thus the mentioned products do not cover the entire range of Earth Radiation Budget products contained in the original dataset provided by Cloud_cci.

1. Instruments

The brokered Cloud_cci cloud dataset is derived from the ATSR-2 and AATSR instruments, which are described in the Cloud_cci ATBD [D1], Section 2.2.

ICDR data is derived from the Sea and Land Surface Temperature Radiometer (SLSTR), flown on board the Copernicus Sentinel-3 platform. SLSTR is an improved version of the ATSR instruments, providing additional spectral channels, improved spatial resolution for the visible and shortwave-infrared channels and a considerably wider swath (1,400 km nadir swath, compared to 512 km for AATSR). As part of the Copernicus operational observation system, two SLSTR instruments are kept operational, with a backup instrument also to be in orbit (although not yet launched). The two operational instruments were launched on Sentinel-3A on 16^th February 2016 and Sentinel-3B on 25^th April 2018. The two platforms fly in identical, interleaved sun-synchronous orbits, such that the two SLSTR instruments provide nearly global coverage twice daily (with one day and one night overpass). Orbital characteristics of Sentinel-3A are summarised in Table 1‑1.

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Table 1‑1: The orbital characteristics of the Sentinel-3 satellites. Note that these characteristics are very similar to the ERS-2 and ENVISAT platforms which carried the preceding ATSR instruments.

The SLSTR instrument is described in detail by the Sentinel-3 SLSTR User Guide [D11], but an overview of its specifications is given in Table 1‑2.

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Table 1‑2: The specifications of the SLSTR instruments (taken from the SLSTR User Guide [D11]).

2. Input and auxiliary data

This section summarises the required input data used in the retrieval algorithms.

2.1 Fundamental climate data record

The input data for the Cloud_cci dataset is the so-called AATSR-multi-mission level 1b data record, and this forms the Fundamental Climate Data Record (FCDR) for this product. The processing of measured radiances to level 1b is described in the ESA AATSR Detailed Processing Model Level 1b [D9] and ENVISAT-style products for ATSR-1 and ATSR-2 data [D10] documents.

The input data for the Cloud_cci extension ICDR is the (non near-real-time) ESA Observation mode SLSTR level-1 archive, hosted by the Centre for Environmental Data Analysis (CEDA). At time of writing, no reprocessing of the SLSTR level-1 archive has been undertaken, and improvements in instrument calibration, pixel colocation/geolocation and minor product details have continued to evolve throughout the lifetime of the mission. It is likely that some variation in ERB product quality will be attributable to this inconsistency in the level-1 input data.

The Broadband Radiative Flux Retrieval (BRFR) module of the CC4CL processor operates on level 2 Cloud_cci cloud products, as well as level 2 aerosol optical depth products produced for the Aerosol_cci project and C3S 312b Lot2, also using the ORAC retrieval scheme applied to (A)ATSR and SLSTR data. Details of the Aerosol retrieval scheme employed for Aerosol_cci and C3S can be found in the Aerosol_cci ORAC ATBD [D6].

2.2 Specific input and auxiliary data

The specific spectral channels used in producing the (A)ASTR and SLSTR Earth Radiation Budget product are detailed in Table 2 1, which were chosen to match the so-called "heritage-channels" provided by the long-running AVHRR instrument series. The cloud retrieval only makes use of the nadir view of the (A)ATSR and SLSTR instruments.

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Table 2-1: (A)ATSR and SLSTR channels used to produce the Cloud_cci Earth Radiation Budget v3.0 TCDR and SLSTR v3.x ICDR

In addition to (A)ATSR or SLSTR level 1 data, the CC4CL retrieval scheme, and BRFR module, also rely on a range of auxiliary datasets, which are detailed in Table 2 2.

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Table 2-2: Auxiliary data used in generating the SLSTR cloud properties and radiation ICDRs.

Further details of the auxiliary data used are provided in the Cloud_cci CC4CL ATBD [D3], Section 3. Full details of input data to the BRFR module are given in Section 2.1 of the BRFR ATBD [D5].

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Anchor note1 note1 1The product used is MCD43A1 V006. See the MODIS user guide at https://www.umb.edu/spectralmass/terra_aqua_modis/v006 (accessed 7-May-2020).

3. Algorithms

This section describes the algorithms used to derive the final Earth Radiation Budget products.

3.1 Retrieval of swath-based Earth radiation (level-2 data)

The algorithm used to derive top-of-atmosphere (and surface) radiation is described in Section 2.1 of the Cloud_cci BRFR ATBD [D5].

3.2 Generation of final products (level-3 data)

The generation of the final level-3 products (monthly means) is outlined in Cloud_cci ATBD [D1], Section 4.

4. Output data

This section summarises information on the output files.

4.1 File format

Cloud_cci TCDR and SLSTR ICDR products are provided to the CDS 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-INSTORACPLATFORM{}YYYYMM{_}_fv3.0.nc,

where INST and PLATFORM refer to the instrument and platform from which data originates (either ATSR2 and ERS2, or AATSR and ENVISAT for TCDR data, or SLSTR and Sentinel-3a or -3b for ICDR data), and YYYYMM provides the year and month covered by the monthly mean product.
Data are provided as monthly means of Earth Radiation Budget, as described in Table 4-1, 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).

4.2 File contents

All data arrays, described in Table 4-1, are 720x360 element arrays, on the grid defined by the longitude (lon, with 720 elements) and latitude (lat, with 360 elements) axes. In addition, each file contains the global attributes defined in Table 4-2.

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Table 4-1: The data variables included in the Cloud_cci TCDR and SLSTR ICDR Earth Radiation Budget files brokered to, or produced for, the CDS.

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Table 4-2: List of global attributes included in the Cloud_cci TCDR and SLSTR ICDR Earth Radiation Budget files brokered to, or produced for, the CDS.

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references references

References

References are listed in ESA Cloud_cci ATBD [D1], Section 5; in ESA Cloud_cci PUG [D2], Section 6; in ESA Cloud_cci CECR [D4], Section 11; in ESA Cloud_cci BRFR ATBD [D5], Section 4; in AATSR Level 1b Detailed Processing Model [D9], Section 3; in ENVISAT-style Products for ATSR-1 and ATSR-2 data [D10], Section 8; and Sus et al. and McGarragh et al. [D7, D8].

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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or 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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