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History of modifications
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List of datasets covered by this document
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Acronyms
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Scope of the document
This document provides information on how to use the satellite-based estimates of cloud properties 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 (daily and 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 CCI documentation, but produced only in the scope of the brokering to the CDS.
Executive summary
The ESA Climate Change Initiative (CCI) Cloud Properties 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.
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This CDR is partnered with the ICDR produced from the Sentinel-3 Sea and Land Surface Temperature Radiometers (SLSTR). The CDR provides level-3 data (monthly means) on a regular global latitude-longitude grid (with a resolution of 0.5°x 0.5°) as well as level-2 data (daily means) on a regular global latitude-longitude grid (with a resolution of 0.1°x 0.1°) and includes these products: cloud fractional cover (CFC), cloud phase (water/ice), cloud optical thickness (COT), cloud particle effective radius (CER), cloud liquid/ice water path (LWP/IWP), and cloud-top pressure (CTP), height (CTH) and temperature (CTT).
1. Cloud_cci global monthly cloud products
The Cloud_cci global monthly cloud properties 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 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. 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 cloud properties 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
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The Cloud_cci product brokered to the CDS consists of cloud properties derived from the ATSR instruments; specifically:
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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 cloud 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 cloud properties.
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Quantity | Cloud_cci variable | Targets |
Cloud amount | CFC |
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Cloud top pressure | CTP |
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Cloud top temperature | CTT |
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Cloud Optical Depth | COT |
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Cloud Water Path | LWP, IWP |
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Effective particle radius | CER |
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1.3 Data usage information
Cloud_cci and SLSTR ICDR 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:
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- The narrow swath of the (A)ATSR instruments means that it requires approximately three days of measurements to provide full global coverage.
- The sun-synchronous orbit used by ERS-2, ENVISAT and Sentinel-3, means that observations are made near two fixed local solar times At high latitudes temporal sampling becomes somewhat better, as adjacent orbits overlap.; 10:00 and 22:00 for the descending and ascending halves of the ENVISAT and Sentinel-3 orbit, and 10:30 and 22:30 for ERS-2. Thus, the diurnal cycle is poorly sampled.
1.3.1 Uncertainties
The ORAC retrieval algorithm is an implementation of Optimal Estimation (Rodgers, 2000) and as such provides uncertainty estimates on all retrieved parameters, propagated from the uncertainty in the input satellite measurements (as well as any forward modelling error included in the uncertainty calculations). The propagation of the L2 uncertainty into L3 products, such as those brokered to the CDS, is not straight forward. Users should refer to the Cloud_cci Comprehensive Error Characterisation Report [D3].
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1At high latitudes temporal sampling becomes somewhat better, as adjacent orbits overlap. |
2. Cloud_cci global daily cloud products
The Cloud_cci global daily cloud properties 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 CDR. Although the format of the brokered data products differs from the official Cloud_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 daily mean global cloud properties over land and ocean from the Along Track Scanning Radiometer (ATSR) series of satellite sensors, on a 0.1×0.1° 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.
2.1 Product description
The Cloud_cci product brokered to the CDS consists of cloud properties derived from the ATSR instruments; specifically:
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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.
2.2 Target requirements
The target requirements for cloud 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 2-1 provides an overview of the GCOS requirements for cloud properties.
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Quantity | Cloud_cci variable | Targets |
Cloud amount | CFC |
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Cloud top pressure | CTP |
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Cloud top temperature | CTT |
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Cloud Optical Depth | COT |
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Cloud Water Path | LWP, IWP |
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Effective particle radius | CER |
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2.3 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:
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For lists and details of known issues and limitations of the data, the user is referred to the referenced ATBDs and papers in Section 1.1.
2.3.1 Uncertainties
The ORAC retrieval algorithm is an implementation of Optimal Estimation (Rodgers, 2000) and as such provides uncertainty estimates on all retrieved parameters, propagated from the uncertainty in the input satellite measurements (as well as any forward modelling error included in the uncertainty calculations). The propagation of the L2 uncertainty into L3 products, such as those brokered to the CDS, is not straight forward. Users should refer to the Cloud_cci Comprehensive Error Characterisation Report [D3].
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where σ2std is the unweighted standard deviation about the mean and c is the correlation between the L2 pixels.
3. Data access information
3.1 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.
3.2 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 be also provided.
3.3 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.
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Bennartz, R., 2017: Error propagation in the generation of gridded satellite datasets, DWD Visiting Scientist Report.
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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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