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Contributors: E. Carboni (UKRI-STFC RAL Space), G.E. Thomas (UKRI-STFC RAL Space)
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List of datasets covered by this document
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Acronyms
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Acronym
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Definition
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AATSR
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Advanced Along-Track Scanning Radiometer
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AMSR-E
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Advanced Microwave Scanning Radiometer - EOS
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ATBD
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Algorithm Theoretical Basis Document
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ATSR
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Along-Track Scanning Radiometer
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C3S
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Copernicus Climate Change Service
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CALIOP
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Cloud-Aerosol Lidar with Orthogonal Polarization
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CCI
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Climate Change Initiative
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CDR
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Climate Data Record
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CDS
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Climate Data Store
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CER
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Cloud Effective Radius
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CFC
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Cloud Fractional Cover
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COT
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Cloud Optical Thickness
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CTH
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Cloud Top Height
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CTP
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Cloud Top Pressure
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CTT
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Cloud Top Temperature
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CWP
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Cloud Water Path
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DARDAR
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raDAR/liDAR
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ENVISAT
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Environmental Satellite
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ERS
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European Research Satellite
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ICDR
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Interim CDR
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IWP
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Ice Water Path
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LWP
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Liquid Water Path
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MODIS
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Moderate Resolution Imaging Spectroradiometer
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RAL
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Rutherford Appleton Laboratory
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RMSE
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Root Mean Squared Error
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SLSTR
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Sea and Land Surface Temperature Radiometer
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STFC
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Science and Technology Facilities Council
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SYNOP
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Surface synoptic observations
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TCDR
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Thematic Climate Data Record
Scope of the document
This document provides a description of the product validation methodology for the global Cloud Properties Climate Data Record (CDR). These products are brokered to (in case of (A)ATSR) or produced for the Climate Data Store (in the case of SLSTR) by the Copernicus Climate Change Services (C3S).
ESA’s Cloud_cci ATSR2-AATSR version 3.0 (Level-3C) dataset, produced by STFC RAL Space from the second Along-Track Scanning Radiometer (ATSR-2) on board the second European Remote Sensing Satellite (ERS-2) spanned 1995-2003, the Advanced ATSR (AATSR) on board ENVISAT spanned 2002-2012. In addition the SLSTR on board of Sentinel-3 spans from 2017 to present and forms the ICDR. The validation for the ICDR is over the period from January 2017 to December 2019. The retrieval algorithm is presented in [D2] and the validation methodology refers to the Cloud_cci Product Validation and Intercomparison Report [D1]. The same methodology is applied to SLSTR dataset.
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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 STFC RAL Space, using the Community Cloud for Climate (CC4CL) processor, based on the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm.
The Cloud_cci dataset comprises 17 years (1995-2012) of satellite-based measurements derived from the Along Track Scanning Radiometers (ATSR-2 and AATSR) on board the ESA second European Research Satellite (ERS-2) and ENVISAT. This TCDR is partnered with the ICDR produced from the Sentinel-3A SLSTR, beginning in 2017, and Sentinel-3B SLSTR beginning in October 2018.
The TCDR and ICDR provide level-3 data, monthly means on a regular global latitude-longitude grid (with a resolution of 0.5 0.5) and daily data (with a resolution of 0.10.1) and includes these products: Cloud Fractional Cover (CFC), Cloud Phase (water/ice), Cloud Optical Thickness (COT), Cloud particle Effective Radius (CER), Liquid/Ice Water Path (LWP/IWP), and Cloud Top Pressure (CTP), Height (CTH) and Temperature (CTT).
1. Validated products
The Cloud_cci ATSR2-AATSR Cloud Properties CDR, version 3.0, is brokered to the CDS from the ESA Cloud_cci project and produced by STFC RAL. 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.
These Cloud Properties datasets from polar orbiting satellites consist of: Cloud Fractional Cover (CFC), Cloud Top Pressure (CTP), Cloud Top Height (CTH), Cloud Top Temperature (CTT), Cloud Effective Radius (CER), Cloud Optical Thickness (COT), Liquid Water Path (LWP), Ice Water Path (IWP) and Cloud Water Path (CWP).
The datasets cover the period from June 1995 to April 2012 (TCDR) of satellite-based measurements derived from ATSR2 and AATSR onboard the polar orbiting ERS-2 and ENVISAT respectively, and the period from January 2017 onwards using the SLSTR measurements (ICDR).These are level 3 products (daily and monthly means) on a regular global latitude-longitude grid (with 0.1° x 0.1° resolution for the daily mean files and 0.5° x 0.5° resolution for the monthly mean files).
ESA’s Cloud_cci dataset on cloud properties, version 3, is the Climate Data Record used for generation of the brokered cloud properties dataset. (DOI: https://doi.org/10.5676/DWD/ESA_Cloud_cci/ATSR2-AATSR/V003).
The Cloud_cci dataset can be downloaded here: https://climate.esa.int/en/projects/cloud/data/. The SLSTR based ICDR extends the coverage, with a five year gap, from 2017 onwards and is only available through Copernicus Climate Data Store (CDS).
Poulsen et al. (2019) [D3] is the paper describing the TCDR dataset that includes cloud products as well as Surface Radiation Budget and Earth Radiation Budget products.
The Product Validation and Intercomparison Report [D1] is the document with validation and intercomparison of cloud properties against other satellite and ground datasets.
2. Description of validating datasets
The Cloud Properties TCDR from ATSR2 and AATSR instruments are validated against CALIOP for cloud fractional cover, and cloud top height.
The cloud top pressure, cloud optical thickness and cloud effective radius (for both liquid and ice cloud) are compared against MODIS Collection 6.1 Terra.
Liquid water path is validated against AMSR-E products and ice water path is validated against the DARDAR IWP product.
We used the CALIOP level-2 1 km and 5 km cloud layer data record versions 3-01, 3-02 and 3-30 ( (https://www-calipso.larc.nasa.gov/) for the validation purpose of cloud fraction and cloud top height.
The MODIS (or Moderate Resolution Imaging Spectroradiometer) 6.1 Terra monthly datasets are available here: https://modis-atmosphere.gsfc.nasa.gov/products/monthly. For the validation we used the data from MODIS Collection 6.1 Terra (dx.doi.org/10.5067/MODIS/MOD08_M3.061).
The Advanced Microwave Scanning Radiometer – EOS (AMSR-E) LWP products can be found here: https://nsidc.org/data/ae_ocean/
The DARDAR data has been downloaded from the University of Lille site:
https://www.icare.univ-lille.fr/dardar/
More details on the datasets used for the validation are described in [D1] section 2.4.2 and Annex A.
3. Description of product validation methodology
The validation strategy is described in [D1] section 2.4. We use the bias, i.e. mean difference between Cloud_cci and the reference data, as the metric for accuracy. The bias corrected root mean squared error (bc-RMSE) is used to express the precision of CDR compared to a reference data record. The stability is the variation of the bias over a multi-annual time period.
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Bias (accuracy):
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Mean difference between Cloud_cci and reference data
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bc-RMSE (precision):
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Bias corrected root mean squared error to express the precision of Cloud_cci compared to a reference data record
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Stability:
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The variation of the bias over a multi-annual time period.
TCDR evaluation is divided into: (i) validation against high quality and satellite-based reference observations (CALIOP, DARDAR and AMSR-E) and (ii) an intercomparison with well-established, satellite-based cloud datasets of similar kind (MODIS).
ICDR data are only validated against MODIS dataset following the same methodology described in section 4.1 of [D1].
3.1 Cloud Fractional Cover (CFC)
Cloud Fractional Cover (CFC) from TCDR is validated against SYNOP in [D1] section 3.2, validated against CALIOP in [D1] section 3.1.1 and compared with MODIS in [D1] section 4.1.1. The validation methodology can be found in the corresponding sections.
ICDR CFC is compared against MODIS using the same methodology described in [D1] section 4.4.1.
3.2 Cloud Top Height (CTH)
Cloud Top Height is validated against the CALIOP data and the validation methodology is described in [D1] section 3.1.3.
ICDR CTH is indirectly validated trough CTP comparison with MODIS.
3.3 Cloud Top Pressure (CTP), Cloud Optical Thickness (COT) and Cloud Effective Radius (CER)
For the TCDR these parameters are compared against MODIS Collection 6.1. Cloud Top Pressure (CTP) is compared in [D1] section 4.1.2, Cloud Effective Radius (CER) is compared in [D1] section 4.1.5 and 4.1.6 and the Cloud Optical Thickness (COT), is compared in [D1] section 4.1.3 and 4.1.4 for the liquid and ice cloud phase. The comparison methodology is described in the corresponding section introduction, 4.1 [D1]. The ICDR uses the same methodology as the TCDR.
3.4 Cloud Liquid Water Path (LWP) and cloud Ice Water Path (IWP)
For the TCDR, Cloud Liquid Water Path (LWP) is validated in [D1] section 3.1.4 against AMSR-E products and compared with MODIS Collection 6.1 in [D1] section 4.1.7. The validation and comparison methodology is described in the mentioned sections.
For the TCDR, Cloud Ice Water Path (IWP) is validated against DARDAR IWP product in [D1] section 3.1.5 and compared with MODIS Collection 6.1 in section 4.1.8. The validation and comparison methodology can be found in the corresponding sections.
For the ICDR, data re compared with MODIS only, according to the methodology described in [D1] section 4.1.
4. Summary of validation results
The validation results for TCDR are provided in [D1] section 7, together with recommendation for use. Here is an extract from table 7-2 in [D1]:
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Comments from [D1]
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Cloud fractional cover
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Accuracy
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Level-2 validation against CALIOP
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Values taken from Table 4-2 and Table 4-13 (L3C comparisons to MODIS C6.1)
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Cloud top height/ pressure
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Accuracy
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0.12km (liquid cloud)
-1.76km (ice cloud)
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Level-2 validation against CALIOP
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Stability (per decade)
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Values taken from Table 4-4 and Table 4-15 (L3C comparisons to MODIS C6.1)
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Liquid cloud optical depth
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Accuracy
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n/v
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No validation possible due to a lack of reliable reference data. through LWP and IWP validation
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Stability (per decade)
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Values taken from Table 4-5 and Table 4-16 divided by mean MODIS C6.1 Terra COTliq (13) (L3C comparisons to MODIS C6.1)
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No validation possible due to a lack of reliable reference data. through LWP and IWP validation
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Values taken from Table 4-6 and Table 4-17 divided by mean MODIS C6.1 Terra COTice (10) (L3C comparisons to MODIS C6.1)
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Level-2 validation against AMSR-E (Figure 3-1)
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Values taken from Table 4-9 and Table 4-20 divided by mean MODIS C6 LWP (123g/m²) (L3C comparisons to MODIS C6)
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Ice water path
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Accuracy
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-39.9%
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Level-2 validation against DARDAR
(Figure 3-2)
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Scope of the document
This Algorithm Theoretical Basis Document (ATBD) describes the generation of the Climate Data Record (CDR) on cloud properties brokered from ESA's Cloud_cci programme 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 ESA Cloud_cci ATBDs [D1, D2], the ESA Cloud_cci Product User Guide (PUG) [D3], and the ESA Cloud_cci Error characterization report [D4]. These documents describe the data processing chain and the algorithms used to generate the cloud property products. The assessment described in this document is carried out within the scope of C3S and 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 cloud properties is a product of the CC4CL dataset produced by ESA's Cloud_cci project and brokered to C3S, and the SLSTR ICDR is an extension to the brokered product. Accordingly, this document largely refers to the ESA Cloud_cci documentation.
The Cloud_cci record contains 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 to C3S comprises daily (0.1° x 0.1° resolution), and monthly (0.5° x 0.5° resolution) means of cloud properties on a regular global latitude-longitude grid. The SLSTR ICDR continues this record, with a 5-year gap, with version v3.x providing cloud products from SLSTR from 2017 on.
The provided cloud products are cloud fractional cover, cloud top level (consisting of cloud top temperature, pressure, and height), and cloud physical properties (consisting of cloud optical thickness, effective radius, and water path for both the liquid and the ice phase). Note that the brokered service within Copernicus provides only a subset of the original CCI cloud properties dataset, thus the mentioned products do not cover the entire range on cloud 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 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. The 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 16th February 2016 and Sentinel-3B on 25th 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.
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.Anchor table1_1 table1_1
Altitude | Inclination | Period | Repeat Cycle | Ground-track deviation | Local Time at Descending node |
814.5 km | 98.65° | 100.99 min | 27 days | ±1 km | 10:00 |
The SLSTR instrument is described in detail by the Sentinel-3 SLSTR User Guide [D10], but an overview of its specifications is given in Table 1‑2.
Table 1‑2: The specifications of the SLSTR instruments (taken from the SLSTR User Guide [D10]).Anchor table1_2 table1_2
Capability | SLSTR Specifications | |
Swath | Nadir view | 1,400 km |
Oblique view | 740 km | |
Global Coverage Revisit Times | 1 satellite | 1 day (mean) |
2 satellites | 0.5 day (mean) | |
Spatial Sampling interval at Sub-satellite point (km) | VIS-SWIR | 0.5 km |
IR-Fire | 1 km | |
Spectral channel centre (µm) | VIS | 0.554 (S1); 0.659 (S2) 0.868 (S3) |
SWIR | 1.374 (S4); 1.613 (S5); 2.25 (S6) | |
MWIR/TIR | 3.742 (S7); 10.85 (S8); 12.02 (S9) | |
Fire ½ | 3.742 (F1); 10.85 (F2) | |
Radiometric Resolution | VIS (Albedo =0.5%) | Signal-to-Noise Ratio (SNR) > 20 |
SWIR (Albedo =0.5%) | Signal-to-Noise Ratio (SNR) > 20 | |
MWIR (T =270K) | NEΔT < 80 mK | |
TIR (T=270K) | NEΔT < 50 mK | |
Fire 1 (<500 K) | NEΔT < 1 K | |
Fire 2 (<400 K) | NEΔT < 0.5 K | |
Radiometric Accuracy | VIS-SWIR (Albedo = 2-100%) | < 2% (Beginning of Life) |
<5% (End of Life) | ||
MWIR –TIR(265 – 310 K) | < 0.2 K (0.1 K goal) | |
Fire (< 500 K) | < 3 K |
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This section summarises the required input data used in the retrieval algorithms.
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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 for this product. The processing of measured radiances to level 1b is described in the ESA AATSR Detailed Processing Model Level 1b [D8] and ENVISAT-style products for ATSR-1 and ATSR-2 data [D9] documents.
The input data for the SLSTR 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 cloud product quality will be attributable to this inconsistency in the level-1 input data.
SLSTR level-1 data is provided in NetCDF-4 formatted files, which are segregated into 3-minute frames. The level-1 data provide TOA reflectance (for visible and SWIR channels) and brightness temperature (for TIR channels), pixel viewing geometry, measurement time and geolocation, as well as other auxiliary information (see the SLSTR User Guide [D10] for further details).
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The specific spectral channels used in producing the (A)ASTR and SLSTR cloud properties datasets 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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(A)ATSR Channel number | SLSTR Band name | Nominal wavelength |
2 | S2 | 0.67 m |
3 | S3 | 0.87 m |
4 | S5 | 1.6 m |
6 | S8 | 10.8 m |
7 | S9 | 12.0 m |
In addition to (A)ATSR or SLSTR level 1 data, the CC4CL retrieval scheme also relies on a range of auxiliary datasets, which are detailed in Table 2-2.
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ECMWF ERA-Interim | ECMWF reanalysis products provide pressure, temperature, humidity and ozone profiles, as well a priori surface temperature, sea ice extent and near-surface wind speed for ocean surface reflectance calculation. |
MODIS MCD43A1 The product used is MCD43A1 V006. See the MODIS user guide at https://www.umb.edu/spectralmass/terra_aqua_modis/v006 (accessed 7-May-2020). V006 | The MODIS BRDF product provides land-surface reflectance. |
IREMIS UW Baseline Fit | The Global Infrared Land Surface Emissivity (IREMIS) University of Wisconsin-Madison Baseline Fit to the MODIS MOD11 emissivity product provides land-surface emissivity. |
RTTOV | The standard coefficient and database files provided with RTTOV v 12.1 are used, where not superseded by other auxiliary data (as is the case with the emissivity and surface reflectance atlases) |
Further details of the input and auxiliary data used are provided in the Cloud_cci CC4CL ATBD [D2], Section 3.
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This section describes the algorithms used to derive the final cloud properties products.
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The algorithm used to retrieve the level-2 data on the cloud fractional cover is briefly summarised in Cloud_cci ATBD [D1] Section 3.1 and the CC4CL ATBD [D2] Section 2.1. A comprehensive description can be found in Sus et al. 2017 [D6].
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3.1.2 Cloud physical properties
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The algorithm used to retrieve the level-2 data on the cloud physical properties is briefly summarised in Cloud_cci ATBD [D1], Section 3.3. Detailed descriptions can be found in the CC4CL ATBD [D2] and McGarragh et al 2017 [D7].
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3.2.1 Cloud fractional cover
Error budget estimates of cloud fractional cover as well as assumptions and limitations associated with the retrieval algorithms are found in the Cloud_cci Comprehensive Error Characterisation Report [D4].
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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). |
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Error budget estimates of cloud physical properties as well as assumptions and limitations associated with the retrieval algorithms are found in the Cloud_cci CC4CL ATBD [D2] Section 2 and the Comprehensive Error Characterisation Report [D4].
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The generation of the final level-3 products (the daily and monthly means) is outlined in Cloud_cci ATBD [D1], Section 4. Note that within the scope of this project, the provided dataset constitutes only a subset of the original Cloud_cci cloud properties dataset. The Cloud_cci PUG [D3] Annex C and the Cloud_cci Comprehensive Error Characterisation Report [D4] Section 6.1 describe the propagation of uncertainty into L3 products.
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Details on the level-3 cloud fractional cover retrieval are given in Cloud_cci ATBD [D1] Section 4.2.1.
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Details on the level-3 cloud physical properties retrieval are given in Cloud_cci ATBD [D1] Section 4.2.2.
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This section summarises information on the output files.
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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-CLD-INSTORACPLATFORM{}YYYYMM{_}_fv3.0.nc,
or
C3S-312bL1-L3C-DAILY-CLD-INSTORACPLATFORM{}YYYYMMDD{_}_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 or YYYYMMDD provide the year, month and (in the case of daily products) day covered by the mean product.
Data are provided as monthly and daily means of cloud properties, as described in Table 4-1 and 4-2, on a regular latitude-longitude grid. For monthly products this grid has 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). Daily products have a grid spacing of 0.1° in both dimensions.
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The data in the monthly cloud products are given in Table 4‑1, while those for the daily products are given in Table 4‑2. Most data fields have four related variables, which are the mean value of the data itself (for example, the mean cloud-top pressure is found in the ctp variable), followed by the standard deviation of the data, denoted by _std, the propagated uncertainty, denoted by _unc, and the spatially correlated uncertainty, denoted by _cor. The definition and details of the calculation of these terms is given in the Cloud_cci Comprehensive Error Characterisation Report [D4].
Both daily and monthly data files have common global attributes, which are defined in Table 4‑3. All data arrays (aside from the lat/lon arrays defining the geographic grid) in the monthly products are 720×360 element arrays, while those in the daily files are 3600×1800 elements. In the case of daily files, data are separated into daylight and night data, based on a solar zenith angle cut-off. This separation is done for two main reasons:
- In locations where the daylight (descending half of the orbit) and night sections (ascending half of the orbit) overlap, data values separated in time by approximately 12 hours would be combined if a simple daily average was taken. Not only can such an average not be considered a valid daily mean, but will result in inconsistent results in adjacent sections of the orbit track which do and do-not overlap
- Cloud optical depth and effective radius rely on information for the shortwave (A)ATSR or SLSTR channels, and thus are not retrieved for night pixels. Thus, in order to provide a consistent set of cloud properties for each retrieval, only daylight cloud top pressure, height and temperature as well as water path should be included in the averaging where effective radius and optical depth are present.
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Property | Unit | Variable name | Comment |
Latitude | Degrees North | lat | Values correspond to grid centres (-89.75°, -89.25°, -88.75°, …, 89.75°). |
Longitude | Degrees East | lon | Values correspond to grid centres (-179.75°, -179.25°, -178.75°, …, 179.75°). |
Cloud pixel count | - | pixel_count | The number of level 2 cloud pixels included in the averaging. Totals are given for all pixels and daylight pixels. |
Liquid cloud pixel count | - | liquid_count | The number of level2 pixels, classified as liquid water cloud, included in the averaging. Totals are given for all pixels and daylight pixels. |
Ice cloud pixel count | - | ice_count | The number of level2 pixels, classified as ice water cloud, included in the averaging. Totals are given for all pixels and daylight pixels. |
Cloud fractional cover | - | cfc | The cloud fractional-area cover, defined as the fraction of level 2 pixels within each level 3 grid cell flagged as cloudy. |
Cloud-top pressure | hPa | ctp | The pressure at the cloud top, as determined from thermal infrared emission. This value is directly related to cth and ctt by ECMWF ERA profiles. |
Cloud-top height | km | cth | The height of the cloud top above mean sea level, determined from thermal infrared emission. This value is directly related to ctp and ctt by ECMWF ERA profiles. |
Cloud-top temperature | K | ctt | The temperature at cloud top, determined from thermal infrared emission. This value is directly related to ctp and cth by ECMWF ERA profiles. |
Cloud effective radius | µm | cer | The effective radius of cloud droplets or ice crystals. |
Cloud optical thickness | - | cot | The column optical thickness at a wavelength of 500 nm. |
Liquid water path | gm-2 | lwp | The column mass of liquid cloud water. |
Ice water path | gm-2 | iwp | The column mass of ice cloud water. |
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Property | Unit | Variable name | Comment |
Latitude | Degrees North | lat | Values correspond to grid centres (-89.95°, -89.85°, -89.75°, …, 89.95°). |
Longitude | Degrees East | lon | Values correspond to grid centres (-179.95°, -179.85°, -179.75°, …, 179.95°). |
Cloud pixel count | - | pixel_count_day | The number of level 2 cloud pixels included in the averaging. Totals are given for daylight and night pixels separately. |
Liquid cloud pixel count | - | liquid_count_day | The number of level2 pixels, classified as liquid water cloud, included in the averaging. Totals are given for daylight and night pixels separately. |
Ice cloud pixel count | - | ice_count_day | The number of level2 pixels, classified as ice water cloud, included in the averaging. Totals are given for daylight and night pixels separately. |
Cloud fractional cover | - | cfc_day | The cloud fractional-area cover, defined as the fraction of level 2 pixels within each level 3 grid cell flagged as cloudy. |
Cloud-top pressure | hPa | ctp_day | The pressure at the cloud top, as determined from thermal infrared emission. This value is directly related to cth and ctt by ECMWF ERA profiles. |
Cloud-top height | km | cth_day | The height of the cloud top above mean sea level, determined from thermal infrared emission. This value is directly related to ctp and ctt by ECMWF ERA profiles. |
Cloud-top temperature | K | ctt_day | The temperature at cloud top, determined from thermal infrared emission. This value is directly related to ctp and cth by ECMWF ERA profiles. |
Cloud effective radius | µm | cer_day | The effective radius of cloud droplets or ice crystals. |
Cloud optical thickness | - | cot_day | The column optical thickness at a wavelength of 500 nm. |
Liquid water path | gm-2 | lwp_day | The column mass of liquid cloud water. |
Ice water path | gm-2 | iwp_day | The column mass of ice cloud water. |
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Attribute name | Description |
title | Descriptive title of the file contents |
Project | "Climate Change Initiative-European Space Agency" |
product_version | The version number of the product |
conventions | Lists the naming and meta data conventions used |
standard_name_vocabulary | Defines the standard name convention used |
Institution | The source institution of the data |
Source | The source (level 1) data used in the product |
geospatial_lon_resolution | The grid spacing in the longitude axis |
geospatial_lat_resolution | The grid spacing in the latitude axis |
geospatial_lon_min | The minimum longitude covered by the product |
geospatial_lon_max | The maximum longitude covered by the product |
geospatial_lat_min | The minimum latitude covered by the product |
geospatial_lat_max | The maximum latitude covered by the product |
spatial_resolution | Alternative description of the spatial grid used. |
geospatial_vertical_min | Definition of vertical grid used (0 indicated no vertical grid) |
geospatial_vertical_max | Definition of vertical grid used (0 indicated no vertical grid) |
Platform | Satellite platform from which observations originated |
Sensor | Satellite sensor which made the observations used |
creator_email | |
creator_url | |
date_created | ISO date and time string of processing time of the particular file |
creator_name | Alternative for institution |
time_coverage_duration | ISO time string defining temporal coverage of the product |
time_coverage_resolution | ISO time string defining temporal resolution of the product |
references | Link to further information about the product |
history | Brief description of provenance of the product |
summary | Brief description of product contents |
keywords | List of keywords (for data discovery) |
comment | Any further comments on the product not covered by other fields |
license | License conditions of the product |
cdm_data_type | Common Data Model Data Type used in the NetCDF file |
keywords_vocabulary | The standard list from which the keywords have been extracted |
naming_authority | ID string of the institution naming product (and contents) |
tracking_id | An ISO Universally Unique Identifier (UUID) number for the file |
id | A human readable identifier of the product |
time_coverage_start | ISO time string of the start of the product's temporal coverage |
time_coverage_end | ISO time string of the end of the product's temporal coverage |
inputfilelist | List of the primary input files used to create the product |
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References are listed in ESA Cloud_cci ATBD [D1], Section 6; ESA Cloud_cci CC4CL ATBD [D2]; ESA Cloud_cci PUG [D3], Section 6; in ESA Cloud_cci CECR [D4], Section 11; in ESA Cloud_cci ATBD (MLEV) [D5], Section 4; in AATSR Level 1b Detailed Processing Model [D8], Section 3; in ENVISAT-style Products for ATSR-1 and ATSR-2 data [D9], Section 8; and Sus et al. 2017 and McGarragh et al. 2017 [D6, D7].
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Values taken from Table 4-10 and Table 4-21 divided by mean MODIS C6 IWP (208g/m²) (L3C comparisons to MODIS C6)
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No validation possible due to a lack of reliable reference data. through LWP and IWP validation
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Values taken from Table 4-7 and Table 4-18 (L3C comparisons to MODIS C6)
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No validation possible due to a lack of reliable reference data. through LWP and IWP validation
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Values taken from Table 4-8 and Table 4-19 (L3C comparisons to MODIS C6)
Intercomparison (using the monthly mean data from January 2017 to December 2019) of ICDR products with MODIS present biases consistent with values found through the TCDR MODIS comparison (D1, section 4.1) for cloud fractional cover (- 5 %), cloud top pressure (-15 hPa) and liquid water path (-15.0 g/m2), but higher values for ice water path, with global average bias of -31 g/m3 for SLSTR-A and -46 g/m3 for SLSTR-B (TCDR IWP bias with MODIS was -29 g/m3).
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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