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Depending on the data record producer, different product requirements may be applied and they are used to evaluate validation results. An often-used way to handle this is to define several levels of requirements where each level is linked to specific needs or priorities. A three-level approach like the following is rather common:
Requirement | Description |
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Threshold requirement | A product should at least fulfil this level to be considered useful at all. Sometimes the term ‘Breakthrough” is used instead. |
Target requirement | This is the main quality goal for a product. It should reach this level based on the current knowledge on what is reasonable to achieve. |
Optimal requirement | This is a level where a product is considered to perform much better than expected given the current knowledge. |
Satellite product levels
Satellite-based products are often described as belonging to the following condensed description of processing levels, each one with different complexity and information content:
Level | Description |
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Level-0 | Raw data coming directly from satellite sensors, often described as sensor counts. |
Level-1 | Data being enhanced with information on calibration and geolocation. Level-1a: Data with attached calibration and geolocation information Level-1b: Data with applied calibration and attached geolocation information Level-1c: Data with applied calibration and additional layers of geolocation, satellite viewing and solar angle information |
Level-2 | Derived geophysical variables at the same resolution and location as L1 source data. An often-used Level-2 variety is the following: Level-2b: Globally resampled images, two per day per satellite, describing both ascending (passing equator from south) and descending (passing equator from north) nodes. Resampling is based on the principle that the value for the pixel with the lowest satellite zenith angle is chosen in case two or several swaths are overlapping. |
Level-3 | Gridded data with results accumulated over time (e.g., monthly means). |
A more comprehensive definition of all processing levels is given here: https://www.earthdata.nasa.gov/engage/open-data-services-and-software/data-information-policy/data-levels.
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Table 1‑1: Licence overview of the CLARA product family Surface Radiation Products, including products SIS, SDL, SOL, SRS and Net Fluxes. Products marked in blue are taken from the CLARA-A2.1 TCDR and the remaining products are Extra Data Products produced in the C3S project. Anchor table1_1 table1_1
Period | CDR Type | CLARA Product Family | |||
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CLARA-A2.1 | Extra Data Products | ||||
SIS | SDL, SOL | SRS | Net Fluxes | ||
1982 – 2018 | TCDR | CM SAF | CM SAF | C3S | C3S |
01/2019 – 06/2022 | ICDR | CM SAF | C3S | C3S | C3S |
The extra data products are not included in the CLARA-A2.1 dataset and are calculated specifically within the C3S project as complimentary data for enabling the description of the full surface radiation budget. Notice also that the SDL and SOL products for the ICDR could not be provided by CM SAF because of computer environment limitations in producing all products in the ICDR version of CLARA-A2.1. Once again, we repeat that combining all variables in the “CLARA product family” group logically combines all variables which are needed for the full description of the Energy Budget at the surface.
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Table 1‑2: Different AVHRR versions and the lifetime of AVHRR on different platforms. The middle row for AVHRR/3 describes the satellites operated by NOAA and the bottom row the satellites operated by EUMETSAT. Anchor table1_2 table1_2
Sensor | Number of channels | Platform/Lifetime | |||||||||||||
AVHRR/2 | 5 | NOAA-7,9,11,12,14 | 1982-2002 | ||||||||||||
AVHRR/3 | 6 | NOAA-15,16,17,18,19 | 1998-onward | ||||||||||||
AVHRR/3 | 6 |
| MetOp-A, B, C | 2006-onward |
The retrieval of the shortwave surface radiation parameters is based on an estimation of the atmospheric transmission and the associated reflected irradiance at the surface. The retrieval of the longwave surface radiation parameters is based on the cloud information from a combination of CLARA-A2.1 cloud products, reanalysis data and topographic information.
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Anchor | ||||
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CLARA Long Names | CF Standard names |
Surface Incoming Shortwave Radiation (SIS, 1) | Surface downwelling shortwave flux |
Surface Downwelling Longwave Radiation (SDL, 4) | Surface downwelling longwave flux |
Surface Outgoing Longwave Radiation (SOL, 5) | Surface upwelling longwave flux |
Surface Reflected Shortwave (SRS, 2) | Surface upwelling shortwave flux |
Surface Net Shortwave Radiation (SNS, 3) | Surface net downward shortwave flux |
Surface Net Longwave Radiation (SNL, 6) | Surface net downward longwave flux |
Surface Radiation Budget (SRB, 7) | Surface net downward radiative flux |
AVHRR Global Area Coverage (AVHRR GAC) data is the fundamental climate data record (FCDR) used for generation of the seven Surface Radiation Budget datasets, that are presented in the following sub-sections. The detailed description of the algorithm used to generate AVHRR GAC is given in CM SAF ATBD Cloud Products [D5], Section 4.3. Further information on the specific input and auxiliary data can be found in the Algorithm Theoretical Basis Document (ATBD) for this dataset [D1].
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Table 2‑1: Key Performance Indicators (KPIs) or target requirements for surface radiation products. Anchor table2_1 table2_1
Variable | KPI: accuracy Wm-2 | KPI: decadal stability, |
SIS Monthly mean (MM) | 9.5 Wm-2 | 2 Wm-2decade-1 |
SIS Daily mean (DM) | 18.6 Wm-2 | 2 Wm-2decade-1 |
SDL MM | 8.1 Wm-2 | 3 Wm-2decade-1 |
SOL MM | 13.8 Wm-2 | 3 Wm-2decade-1 |
SRS MM | 7.8 Wm-2 | 3 Wm-2decade-1 |
SNS MM | 13.0 Wm-2 | 3 Wm-2decade-1 |
SNL MM | 21.9 Wm-2 | 3 Wm-2decade-1 |
SRB MM | 34.9 Wm-2 | 3 Wm-2decade-1 |
At the time (~2010) when requirements for the CLARA-A2 data record were defined, as described in [D4], there was no guidance available for surface radiation products in the available GCOS-107 document [D6]. Instead, requirements had to be set based on a dialogue with experts and potential users (e.g., in association with CM SAF User Workshops).
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Table 2‑2: Key Performance Indicators (KPIs) for the surface radiation budget ICDR products. Anchor table2_2 table2_2
Variable | KPI: lower percentile (2.5 %), Wm-2 | KPI: higher percentile (97.5 %), Wm-2 |
SIS Monthly mean | 5.27 | 14.66 |
SIS Daily mean | 8.21 | 41.36 |
SDL Monthly mean | 5.11 | 11.63 |
SOL Monthly mean | 8.12 | 25.84 |
2.1.2 Discussion of requirements with respect to GCOS and other requirements
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Table 2‑3: GCOS-200 requirements for surface radiation products compared to CLARA-A2.1 requirement. Anchor table2_3 table2_3
Requirements | GCOS (Target) | CLARA-A2.1 TCDR + ICDR v2.x |
Spatial resolution | 100 km | 25 km |
Temporal resolution | Monthly (resolving diurnal cycle) | Monthly |
Accuracy: | ||
SIS MM | 1 Wm-2 | 9.5 Wm-2 |
SIS DM | 1 Wm-2 | 18.6 Wm-2 |
SDL MM | 1 Wm-2 | 8.1 Wm-2 |
SOL MM | 1 Wm-2 | 13.8 Wm-2 |
SRS MM | 1 Wm-2 | 7.8 Wm-2 |
SNS MM | 1 Wm-2 | 13.0 Wm-2 |
SNL MM | 1 Wm-2 | 21.9 Wm-2 |
SRB MM | 1 Wm-2 | 34.9 Wm-2 |
New GCOS requirements for the ECV Surface Radiation Budget are summarized in GCOS-200 [D7] and include requirements for the horizontal resolution, temporal resolution, accuracy and stability. However, these requirements are only valid for the net fluxes (i.e., SNS and SNL) and not for all individual radiation budget components (see Table 2-4 below). However, one could claim that individual radiation budget components should consequently be constrained in the same way as net fluxes.
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Table 2‑4: Target requirements for surface radiation budget defined by GCOS-200 ([D7], Table 23, page 279]. Anchor table2_4 table2_4
GCOS quantity | Corresponding Cloud_cci variable | GCOS targets |
Surface ERB longwave | Surface net longwave radiation (SNL) |
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Surface ERB shortwave | Surface net solar radiation (SNS) |
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2.2.2 Key Performance Indicators - KPIs
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Table 2‑5: Key performance indicators (KPIs) or target requirements (i.e. fulfilled requirements by the ESA-CLOUD-CCI project) for surface radiation products from ESA_CCI_AATSR TCDR v3.0. Anchor table2_5 table2_5
Variable | KPI: accuracy (Bias) Fulfilled by ESA-CLOUD-CCI | KPI: decadal stability Fulfilled by ESA-CLOUD-CCI |
SIS | 8.2 W/m2 | 0.97 W/m2/decade |
SDL | 12 W/m2 | 2.76 W/m2/decade |
SRS | 4.6 W/m2 | - |
SNS | 13 W/m2 | - |
SOL | 11 W/m2 | - |
SNL | 23 W/m2 | - |
SRB | 36 W/m2 | - |
The Cloud_cci (A)ATSR data record forms the basis for the calculation of KPIs for the SLSTR based ICDR. The KPIs for the SRB products are based on comparison against the NASA Clouds and the Earth's Radiant Energy System (CERES) instruments (Wielicki et al., 1996). These comparisons are represented as the 2.5 and 97.5 percentiles of the distribution of differences between (A)ATSR or SLSTR monthly-mean values and the corresponding CERES values (corrected for the mean seasonal cycle). These values, calculated from the 12-year (A)ATSR CDR are summarized in Table 2-6.
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Table 2‑6: Key performance indicators (KPIs) for the Cloud_cci SRB record, applied to the SLSTR ICDR data. Anchor table2_6 table2_6
Variable | KPI: lower percentile (2.5 %), Wm-2 | KPI: higher percentile (97.5 %), Wm-2 |
SIS Monthly mean | -1.3 | 2.12 |
SRS Monthly mean | -0.45 | 0.36 |
SDL Monthly mean | 1.95 | 2.23 |
SOL Monthly mean | -4.04 | 3.68 |
2.2.3 Discussion of requirements with respect to GCOS and other requirements
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