...
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 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. |
Table 3: Definition of various technical terms used in the document
Jargon | Definition |
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. |
Near-real-time (NRT) | Data which is provided within a short time window (often taken to be three hours, but there is no fixed definition) of the measurement. NRT data is often supplanted by a subsequent data stream, which is subjected to more rigorous checking data quality. |
BUGSrad | The broad-band radiative transfer software used to generate the radiative flux values that make up the SRB CDR. |
Radiative transfer | The mathematical modelling of the interaction of electromagnetic radiation with some medium – in this case solar and thermal-infrared radiation passing through the Earth’s atmosphere. |
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. |
TCDR | It is a consistently-processed time series of a geophysical variable 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. |
CDR | A Climate Data Record (CDR) is defined as a time series of measurements with sufficient length, consistency, and continuity to determine climate variability and change. |
Scope of the document
This Algorithm Theoretical Basis Document (ATBD) is associated with the CDS catalogue entry: Earth’s radiation budget from 1979 to present derived from satellite observations. The ATBD describes the algorithm used to generate the Climate Data Record (CDR) on Earth Radiation Budget, which is a brokered service from the European Space Agency Cloud Climate Change Initiative (ESAs Cloud_cci), and its extension with an interim-CDR (ICDR) derived from the Sea and Land Surface Temperature Radiometer (SLSTR).
...
Table 1-1: The specifications of the (A)ATSR (i.e. ATSR-2 and AATSR) instruments. Anchor table1_1 table1_1
| Capability | (A)ATSR Specifications |
Swath | Nadir view | 512 km |
Oblique view | 512 km | |
Global Coverage Revisit Times | 3-4 day (mean) | |
Spatial Sampling interval at Sub-satellite point (km) | VIS-SWIR | 1 km |
IR | 1 km | |
Spectral channel centre (µm) | VIS | 0.554 (Ch1); 0.659 (Ch2) 0.865 (Ch3) |
SWIR | 1.61 (Ch4) | |
MWIR/TIR | 3.70 (Ch5); 10.85 (Ch6); 12.00 (Ch7) |
Figure 1‑2: Time coverage of ATSR-2, AATSR and SLSTR at the time of writing. Anchor figure1_2 figure1_2
...
Table 1-2: The orbital characteristics of the ERS-2, ENVISAT and Sentinel-3 satellites. Anchor table1_2 table1_2
Platform | Altitude (km) | Inclination | Period (min) | Repeat Cycle (days) | Ground-track deviation | Local Time at Descending node |
ERS-2 | 780 | 98.5° | 100 | 35 | 10:30 | |
ENVISAT | 799.8 | 98.55° | 100.59 | 35 | 10:00 | |
Sentinel-3 | 814.5 | 98.65° | 100.99 | 27 | ±1 km | 10:00 |
The SLSTR instrument is described in detail by the Sentinel-3 SLSTR User Guide (see References), but an overview of its specifications is given in Table 1-3.
Table 1-3: The specifications of the SLSTR instruments (taken from the SLSTR User Guide (see References)). Anchor table1_3 table1_3
| Capability | SLSTR Specifications |
Swath | Nadir view | 1,400 km |
Oblique view | 740 km | |
Global Coverage Revisit Times (nadir view) | 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 | < 0.2 K (0.1 K goal) | |
Fire (< 500 K) | < 3 K |
2. Input and auxiliary data
...
Anchor | ||||
---|---|---|---|---|
|
(A)ATSR Channel number | SLSTR Band name | Nominal wavelength |
2 | S2 | 0.67 µm |
3 | S3 | 0.87 µm |
4 | S5 | 1.6 µm |
6 | S8 | 10.8 µm |
7 | S9 | 12.0 µm |
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.
Anchor | ||||
---|---|---|---|---|
|
Dataset | Description |
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 MCD43A12 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) |
SOHO and SORCE | Up until September 2019, information on incoming total solar irradiance is supplied by the Solar and Heliospheric Observatory (SOHO) and sOlar Radiation and Climate Experiment (SORCE) satellite records. |
NOAA daily TSI CDR and TSIS | From September 2019 on, information on incoming total solar irradiance is supplied by the Total Solar Irradiance CDR produced by NOAA, with measurements from the Total and Spectral Solar Irradiance Sensor (TSIS) on the International Space Station being used for dates too recent to be covered by the NOAA CDR. |
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].
...
Table 3-1: Inputs to the BRFR module. Cloud properties are only required where the cloud-type is not set to clear. Conversely, aerosol optical depth is only utilized for clear pixels. Anchor table3_1 table3_1
BUGSrad input | Data source |
Total solar irradiance (TSI) | SOHO and SORCE, or NOAA daily TSI CDR and TSIS |
Solar zenith angle | ORAC output (from L1 data) |
Direct and diffuse albedo of the surface (visible and near-IR) | Pre-processor output |
Surface temperature | Pre-processor output (ERA5) |
Cloud type (clear-sky, liquid water cloud or ice cloud) | ORAC output |
Cloud-top height | ORAC output |
Cloud optical depth (at 550 nm) | ORAC output |
Cloud effective radius | ORAC output |
Profiles of temperature, pressure, humidity and ozone-concentration, as a function of height. | Pre-processor output (ERA5) |
Aerosol optical depth (optional) | Aerosol_cci L2, C3S aerosol L2 or MODIS L2. |
Info | ||
---|---|---|
| ||
4 C3S does provide SLSTR aerosol products, including one derived using ORAC, but the difference in nadir and oblique swath widths in SLSTR means that aerosol properties are not available for the full swath of the cloud retrievals. |
...
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. Anchor table4_1 table4_1
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°) |
Pixel count | - | pixel_count | The total number of level 2 pixels included in the averaging (both cloudy and clear). |
Cloud pixel count | - | cloud_count | The number of level 2 cloud pixels included in the averaging (NB. Does not include number of Aerosol_cci pixels included). |
Top-of-atmosphere reflected solar flux | Wm-2 | rsf | |
Top-of-atmosphere outgoing longwave radiation | Wm-2 | olr |
Anchor | ||||
---|---|---|---|---|
|
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 |
Anchor | ||||
---|---|---|---|---|
|
...
Content by Label | ||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|