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

Issued by: STFC RAL Space (UKRI-STFC) / Gareth Thomas

Date: 22/02/2023

Ref: C3S2_D312a_Lot1.3.2.2_202302_SQAD_CCI_CP_SRB_ERB_v1.1

Official reference number service contract: 2021/C3S2_312a_Lot1_DWD/SC1

History of modifications

List of datasets covered by this document

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Acronyms

List of tables

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General definitions

Table 1: Definition of processing levels

Table 2: Definition of various technical terms used in the document

Scope of the document

This document describes the systems used for delivering the satellite-based estimates of Cloud Properties (CP), Surface Radiation Budget (SRB), and Earth Radiation Budget (ERB), brokered from ESA´s Cloud_cci ATSR-AATSRv3 dataset or derived from the Sea and Land Surface Temperature Radiometer (SLSTR) specifically for the Copernicus Climate Change Service (C3S). The CP, SRB, and ERB products are produced by the Optimal Estimation of Aerosol and Cloud (ORAC) retrieval scheme, operating as the Community Cloud for Climate (CC4Cl) processor, and provided to the Climate Data Store (CDS) by the C3S. Interfaces to external data, the data processing infrastructure, and the interface to the CDS are outlined. Internal procedures for managing and communicating system maintenance and for user support are described.

Executive summary

All ORAC datasets – brokered (A)ATSR cloud and radiation CDRs and SLSTR cloud and radiation ICDRs – are made available to the CDS using a common architecture. Access is via HTTP access to the CDS-C3S cloud workspace hosted on the JASMIN compute infrastructure provided by the Centre for Environmental Data Analysis (CEDA), or through CEDA’s long-term data archive with FTP, HTTP, or OPeNDAP interfaces available. As a national facility, JASMIN outages are kept to a minimum and, if possible, will be communicated to C3S in advance. We provide user support for queries relating to our products when forwarded to us by C3S (see Section 5 User Support).

1. System overview

1.1 System elements and interfaces

The Cloud_cci ATSR-AATSRv3 dataset has been produced and archived outside of this contract by ESA, whereas the SLSTR extension Interim Climate Data Record (ICDR) is produced specifically for C3S, using the same processing infrastructure as the original Cloud_cci TCDR. Data was produced using the CC4CL cloud processor, with the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm producing cloud properties, which are then fed into the Broadband Radiative Flux Retrieval (BRFR) module to produce the Surface Radiation Budget (SRB) and Earth Radiation Budget (ERB) products. The CC4CL processor consists of a 4 or 5-stage processing chain, depending if only CP products or ERB/SRB products are required, to go from level-1 satellite top-of-atmosphere radiances to level-3 gridded  data:

1. Pre-processing: Reads satellite level-1 data, as well as ancillary data including meteorology data (ECMWF ERA-Interim in the case of the v3 Cloud_cci product and ERA-5 in the case of the SLSTR ICDR) and surface reflectance (MODIS MCD43A1 BRDF¹ product). Clear-sky radiative transfer calculations are done, using RTTOV (version 12), data are co-located onto the level-1 data grid and all inputs required by the ORAC retrieval code are written to disk.
2. Cloud-retrieval: The cloud retrieval is run twice, one assuming water cloud droplets, one assuming ice.
3. Post-processing: This step combines the ice and water cloud retrievals into a unified product, based on which assumption best fit the observations, and the retrieved cloud-top-temperature. This step produces the level-2 cloud product.
4. Flux calculation²: The BRFR module reads the level-2 cloud product, temperature, humidity, ozone and surface reflectance data produced by the pre-processing step, (A)ATSR aerosol_cci level-2 data (also produced by the ORAC processor) and solar irradiance data provided by the Solar and Heliospheric Observatory (SOHO) (https://sohowww.nascom.nasa.gov/) and SOlar Radiation and Climate Experiment (SORCE) (https://lasp.colorado.edu/home/sorce/) satellite records. This step produces the level-2 radiative flux product.
5. Level-3 compositing: Level-2 cloud properties and radiative fluxes are averaged onto the regular lat-lon grid used for the level-3 products. This step produces the level-3 monthly CP, SRB and ERB data provided to C3S.

All steps of this processing are coded in Fortran 2003 and are version controlled using Git. All code, with the exception of the level-3 processor, are publicly accessible, under the GNU General Public License v3, via GitHub (https://github.com/ORAC-CC/orac).

Details of the cloud retrieval algorithm can be found in the ATBD [D1], while the BRFR module has its own ATBD [D2]. Details of the Cloud_cci product in general can be found in the product user guide [D3].

Processing is performed using the Lotus cluster, which provides a large-scale computational resource (approx. 12,000 CPU cores) to the JASMIN super-data-cluster. Use of JASMIN for processing provides the benefit that all required level-1 satellite and ancillary data are available from on-line disk storage. The processing system is run via Python and shell scripts, interfacing to a Slurm³ job-manager. Reformatting of the Cloud_cci level-3 products to meet C3S requirements is performed using run-time IDL code.

1.1.1 Interfaces to external data

Brokered CDR products

The Cloud_cci TCDR is a brokered product, for which processing has been completed. The brokered data is static and self-contained – no further production of version-3 Cloud_cci data will be undertaken.

Interim CDR products

All required input data needed to produce ICDR data from SLSTR is stored on-line on the JASMIN system, including ERA data (which is provided by CEDA) and the auxiliary datasets of MODIS MCD43A1.

1.1.2 Delivery of the data to C3S

Access to Cloud_cci Cloud Properties, Surface Radiation Budget, and Earth Radiation Budget datasets is provided using the same mechanism as used for the CCI project itself, and is replicated for SLSTR ICDR products. Data are provided through an HTTP access to CEDA group-workspace storage until data is transferred into the CEDA archive, after which FTP, HTTP, and OPeNDAP are all available.

The storage (both group-workspace and archive) used for storing the brokered Cloud_cci data and SLSTR ICDR data, as well as the HTTP, FTP, and OPeNDAP interfaces are provided and maintained by CEDA, as part of the UK national computational infrastructure. See section 1.2 for further details of this system.

1.2 Hardware, supercomputers and cloud computing

1.2.1 Computing infrastructure

The UK JASMIN "super-data-cluster", operated by CEDA, provides all the computing infrastructure for production and delivery of ORAC products. JASMIN hosts the UK archive of both (A)ATSR and SLSTR level 1b data, as well as providing on-line access to ECMWF ERA-5 data. Through support from the UK Space Agency, the system also provides approximately 12,000 CPU cores for data production and 250 Tb of storage for data production and provision, dedicated solely for C3S_312b_Lot1.

1.2.2 Back-up

(A)ATSR and SLSTR products are archived and served by the Centre for Environmental Data Analysis (CEDA) which holds multiple tape backups of its archive. Data stored on group-workspace storage are not automatically backed up, but a back-up can be made through a user-accessible elastic tape storage system.

1.2.3 Data access and delivery

The CEDA archive provides HTTP, FTP and OpenDAP access to datasets. Access to data stored on the dedicated C3S_312b_Lot1 group-workspace will be through HTTP only. CEDA provides a target minimum availability of both the archive and workspace servers of 95%, with data transfer rates greater than 10 Mbit/s.

2. Upgrade cycle implementation procedure

The data record provided by the Cloud_cci ATSR-2/AATSR dataset will be extended by the production of an ICDR from the Sea and Land Surface Temperature Radiometer (SLSTR) instrument, flying on board the Sentinel-3 satellites from mid-2016. This record will be updated to include the most recent data on a 6-monthly basis.

3. Procedures for reprocessing CDRs

Within the scope of this project, no reprocessing of the ESA Cloud_cci ATSR-AATSRv3, or SLSTR, cloud properties dataset is foreseen. Therefore n/a.

4. System maintenance and system failures

In general, any issues with IT infrastructure that either delay delivery of data or impede access to data via the CDS will be documented in the Quarterly Report.

4.1 Interfaces to external data

See section 1 above.

4.2 Production of data sets

No data production is required to deliver Cloud_cci (A)ATSR data, as it is an existing, brokered dataset. Production of SLSTR ICDR data makes use of the Lotus cluster, which forms part of the JASMIN infrastructure.

4.3 Interface to the CDS

This section discusses maintenance and outages of the data server hosting the files for access through the CDS.

4.3.1 Planned maintenance

CEDA performs regular maintenance and upgrades of its systems, and these works are undertaken in such a way to minimize impact to users of the system. Scheduled updates and downtime are advertised on the CEDA website and through an RSS feed (http://www.ceda.ac.uk/blog/feeds/rss/).
CEDA also takes the needs of its customers and users into account when planning downtime. These notifications will cover interruptions to input data, processing infrastructure and access to data for C3S.

4.3.2 Unplanned outages

CEDA has a dedicated technical team to deal with unplanned outages, and their helpdesk keeps users informed through emails and news-feed updates. This information will be forwarded on to C3S as required.

5. User support

5.1 Enquiries

The user (customer) has the possibility to browse and search in the Copernicus Knowledge Base (CKB) (CAMS and C3S Knowledge Base (CKB)) or the Copernicus Climate Data Store desk (https://cds.climate.copernicus.eu/cdsapp#!/usersupport) (Figure 5-1). This is known as the level-0 process of User Support.

Contact and User Support process on JIRA service desk

Once a request is sent, the Copernicus User Support (CUS) Service team at ECMWF will handle the requests within 8 hours (level 1).

For any scientific and special enquiries that cannot be answered by the CUS team at ECMWF or addressed to the Knowledge Base, the request will be forwarded to the Copernicus User Support Specialists (level-2).

Enquiries forwarded to the Copernicus User Support Specialist team will be acknowledged within 3 working days (target 100%) and a notification sent to the user. In case of specific scientific issues, the enquiries will be channelled to the ECV and data specialist of the C3S2_312a_Lot1 project and should be resolved within 3 working weeks (target 85%). In each quarter, we aim for User Support satisfaction scoring 3 in 90% of all voluntary based feedbacks by users, with 1 (very unsatisfied) to 5 (very satisfied). We will also list the number of tickets in the Quarterly Report.

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