Last modified on Aug 07, 2023 15:35

Contributors: Nicolas Clerbaux (RMIB), Almudena Velazquez Blazquez (RMIB), Edward Baudrez (RMIB), Gareth Thomas (STFC-RAL)

Issued by: SMHI/Karl-Göran Karlsson

Date: 05/02/2021

Ref: C3S_D1.6.1-2020_202012_TRGAD_ERB_v1

Official reference number service contract: 2018/C3S_312b_Lot1_DWD/SC1

History of modifications

Related documents

Acronyms

General definitions

The meaning of the terms uncertainty, accuracy and error is often difficult to interpret and may be treated differently in various referred documents. In this document, we adopt the following interpretation:
The accuracy, uncertainty or error of an estimated ECV is described by three differently contributing components:

1. The systematic error
2. The random error
3. The time-dependent error

The systematic error is commonly the mean error or the Bias. For non-Gaussian distributions of the error, the median or the mean absolute error can be a more useful quantity.
The random error is commonly the root-mean-squared deviation RMSD. Sometimes, the Bias is subtracted yielding the centered root-mean-squared deviation cRMSD. Notice that if the Bias is zero, the two mentioned quantities are equal and may be interpreted as the standard deviation of the error (often denoted standard error).
The time-dependent error is commonly the change in Bias over time (for ECVs over decades). We call this parameter stability.
More details on the estimation of these parameters are given in the Report on Updated KPIs [D5].

Scope of the document

This document provides relevant information on requirements and gaps for the Earth Radiation Budget (ERB) Essential Climate Variable (ECV).
The document is divided into three parts. Part 1 describes products the present document refers to. Part 2 provides target requirements for the products. Part 3 provides a past, present, and future gap analysis for the products and covers both gaps in the data availability and scientific gaps that could be addressed by further research activities (outside C3S).

Executive summary

The products associated with the Earth Radiation Budget ECV are described together with their target requirements. A description of past, current and future availability of ERB measurements is given. Data coverage is expected to be secured for the next 10 - 15 years if combining LEO and GEO data. Continuity thereafter is still unclear. The use and definition of Earth Radiation Budget parameters are partly dependent on non-measurable quantities like ocean heat content and is therefore vulnerable to changes in the assessment of these quantities. A need to improve angular dependency models for some instruments has been identified. Since the end of measurements from the Terra mission approaches it is suggested to develop ERB products for Metop or Metop-SG satellites. An opportunity to better characterize the error in CERES products is foreseen after the launch of the EarthCARE satellite.

The first ERB product brokered in the C3S CDS is the Cloud and Earth radiant Energy System (CERES) Energy Balanced And Filled (EBAF) product. The target accuracy requirement of both longwave and shortwave upward fluxes is set to 2.5 W m^-2 (RMSD). The stability requirements for longwave fluxes are set to 0.2 W m^-2 decade^-1 and to 0.3 W m² decade^-1 for shortwave fluxes.
Due to the long period coverage, from 1979 onward, the HIRS OLR CDR maintained by NOAA as part of its CDR program is also brokered in the C3S CDS. This CDR is also considered in the document. The HIRS instrument is not present on Metop-C and on NOAA-20. However, HIRS-like data could be generated from the IASI and CrIS instruments. Continuation of the CDR is therefore expected.

Additionally, ERB estimates derived from (A)ATSR are brokered from the ESA Cloud_cci project, with this CDR being extended with the same analysis applied to the SLSTR instruments aboard Sentinel-3 (this ICDR is produced specifically for C3S, rather than being a brokered product like the AATSR TCDR). These products differ from the others, as they are derived through radiative transfer calculations from cloud and aerosol retrieval output, along with surface radiation budget (these associated products are also available through the CDS). Data coverage runs from mid-1995 to early 2012 for the (A)ATSR TCDR, with the SLSTR ICDR beginning in January 2017.
Finally, the CDS also publishes a CDR of daily Total Solar Irradiance (TSI) from a composite of a large set of space instruments. As the TSI is fully part of the ERB it is also discussed in this document.

The time periods covered by ERB records (as of 12/2020) are specified in the following table.

Periods covered by the C3S TCDR and ICDR.

1. Product description

1.1 Earth Radiation Budget CERES TCDR v1.0 + ICDR v1.x (OLR, RSF)

1.1.1 The CERES EBAF CDR

The CERES Energy Balanced and Filled (EBAF) data is "brokered" in the Copernicus Climate Data Store (CDS). The EBAF product is based on the data acquired by the Cloud and Earth's Radiant Energy System (CERES) instruments (Figure 1-1). The CERES instruments are broadband radiometers developed as part of the NASA's Earth Observing System (EOS) program. Wielicki et al. (1996) provide a description of the CERES instrument as well as of the CERES mission.

Figure 1-1: CERES instrument (left) and program logo (right).

The TOA EBAF file provides a total of 14 parameters which are given in Table 1-1. Among those, only the shortwave and longwave fluxes in all-sky condition are accessible via the CDS. The incoming solar flux is also available via the CDS but as ancillary field of the RSF. It is worth mentioning that these fluxes are provided as a reference level of 20km, to ease the comparison with climate/NWP models (see Loeb et al., 2002).

Table 1-1: Content of the CERES EBAF file

1.1.2 Input data

Table 1-2 details the spacecraft on which the 7 CERES instruments have been launched. The CERES EBAF edition 4.1 relies on the FM1 to FM4 instruments from the EOS Terra and Aqua satellites.

Table 1-2: CERES instrument history.

A brief summary of the input data is given in Table 1-3, while a comprehensive description is provided by Loeb et al. (2018) [D1].

Table 1‑3: Main input and auxiliary data used in processing the CERES EBAF edition 4 CDR.

1.1.3 Algorithm name and version, bias correction

The data comes from EBAF Edition 4. The DOI is 10.5067/TERRA+AQUA/CERES/EBAF-TOA_L3B004.0. However, as the data is fetched directly from NASA’s OPeNDAP servers, the version that is offered through CDS in the future may be more recent. For CERES EBAF, the ICDR has the same characteristics as the TCDR described in the previous sections. There is no change of input data or algorithm. The CERES team regularly adds new data in the EBAF record but does not make a formal difference between “validated” TCDR and “interim” ICDR. The TCDR/ICDR distinction is done in C3S to indicate difference in the level of validation.

 The TOA fluxes have been “balanced” in the EBAF. This consists of a kind of bias correction to make the data compliant with the best estimate of the Earth imbalance (see Loeb et al. 2018; [D1]).

1.2 Earth Radiation Budget HIRS OLR TCDR v1.0

1.2.1 The HIRS OLR CDR

The HIRS OLR product is based on the data acquired by the High Resolution Infrared Radiation Sounder (HIRS) instruments (Figure 1-2) measuring radiances in the infrared (IR).

Figure 1-2: HIRS instrument (left) and NOAA logo (right)

The Outgoing Longwave Radiation (OLR) is the total amount of energy emitted by the Earth and escaping toward the space. This quantity, expressed in W/m², is also called the "longwave flux" or the "thermal flux". Together with the incoming solar radiation and the reflected solar radiation, it is a component of the Top-of-the-Atmosphere (TOA) Earth Radiation Budget (ERB).
The HIRS OLR CDR is widely used by the climate community as an important component of the ERB (Schreck et al., 2018). The OLR can also be used as an accurate indicator of the convection and useful to diagnose the Madden-Julian Oscillation (MJO). OLR is also used for climate model evaluation. It is worth to mention that the HIRS OLR CDR is, along with the CERES products, the only data currently published in Obs4MIPS (Observations for Model Intercomparison Projects, https://esgf-node.llnl.gov/projects/obs4mips/) concerning the ERB. An example of product is given in Figure 1-3.

Figure 1-3: Illustration of the monthly mean HIRS OLR v02r07 *(unit is W/m²).

1.2.2 Input data

The CDR compiles data from 4 successive versions of the HIRS instrument: HIRS/2, HIRS/2I, HIRS/3 and HIRS/4. They are launched on the NOAA and Metop satellites. Table 1-4 details the spacecraft’s and HIRS instrument type used as input for the HIRS OLR CDR.

Table 1‑4: Description of the HIRS instrument type and level-1b data set coverage available for the HIRS OLR CDR production (from [D6]).

The HIRS instrument series is now discontinued and there is no HIRS on Metop-C or on NOAA-20. Significantly improved performances are obtained from the Cross-track Infrared Sounder (CrIS) and Infrared Atmospheric Sounding Interferometer (IASI) instruments.

1.2.3 General characteristics of the product

The general characteristics of the monthly mean HIRS OLR CDR are given by Table 1-5.

Table 1-5: Characteristics of the monthly mean HIRS OLR CDR.

1.3 Earth Radiation Budget TSI TOA TCDR v2.0 + ICDR v2.x

1.3.1 The C3S Total Solar Irradiance CDR

The Total Solar Irradiance (TSI) quantifies the amount of solar energy that reaches the Earth per unit surface perpendicular to the Sun–Earth direction at the mean Sun–Earth distance (i.e. at 1 astronomical unit, AU). It is a fundamental variable governing the climate system, and is recognized as ECV by the GCOS. Within the C3S, a long composite CDR is constructed from TSI measurements from an ensemble of space instruments. The measurements of the individual instruments are first put on a common absolute scale, and their quality is assessed by intercomparison. Then, the composite time series is the average of all available measurements, on a daily basis. Figure 1-4 shows the daily values of the TSI (blue) as well as a rolling mean (orange). The 11-years cycle of solar activity is clearly visible.

Figure 1-4: timeseries of daily C3S TSI (blue) and rolling mean (orange).

1.3.2 Input data

Table 1-6 lists the main space instruments for TSI measurement and indicates the ones used to construct the C3S composite.

: Total Solar Irradiance space instruments (acronyms definitions at beginning of document).

1.3.3 General characteristics of the product

The general characteristics of the product are given by Table 1-7.

: Characteristics of the C3S TSI product (v2.x).

1.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR-based ICDR v3.1 (OLR,RSF)

1.4.1 The Cloud_cci ERB CDR and ICDR

This section describes the ERB products of the Cloud_cci (A)ATSR v3.0 data record, which we will refer to as Cloud_cci v3, and its extension with the same retrieval scheme applied to the Sea and Land Surface Radiometer (SLSTR), which is produced specifically for C3S. The Cloud_cci v3 record is based on Along-Track Scanning Radiometer 2 (ATSR-2) and Advanced A Along-Track Scanning Radiometer (AATSR) observations onboard the ESA 2^nd European Research Satellite (ERS-2) and ENVISAT satellites. Together, the data record provided by these two instruments is often abbreviated to (A)ATSR. The SLSTR instrument, which is the successor to (A)ATSR, is on board the Copernicus Sentinel-3 platform [D15].

Observations are available on a 1x1 km grid, which closely matches the true instrument spatial resolution globally and the final CDR is compiled in a regular global grid with 0.5° latitude-longitude resolution for monthly averages. The covered time period of the Cloud_cci data record ranges from June 1995 to April 2012 (with a 6-month gap from January – June 1996) and the SLSTR extension provides coverage from January 2017; i.e. there is an almost seven-year gap between the TCDR and corresponding ICDR.

The product was produced using the Community Cloud four Climate (CC4Cl) processing chain, which is based around the Optimal Retrieval of Aerosol and Cloud (ORAC) retrieval scheme, both of which are described in detail in [D16, D17] and by Sus et al. (2018) and McGarragh et al. (2018). The primary product of this retrieval chain are cloud properties, but these are used, in conjunction with aerosol properties also derived from (A)ATSR or SLSTR using the ORAC retrieval, as inputs to the Bugsrad radiative transfer scheme to derive broadband radiative fluxes at both the surface and TOA. The two values provided to the CDS in the Cloud_cci v3 ERB product are the Reflected Solar Flux (RSF) and Outgoing Longwave Radiation (OLR).

1.4.2 Input data

The Cloud_cci TCDR products were based on the third reprocessing of the AATSR-multimission archive, which included vicarious calibration of the shortwave channels over the entire data record to correct for long-term calibration drift (Smith, 2012). SLSTR ICDR products are based on collection 3 of the "non-time critical" SLSTR level 1 archive. In addition, the CC4Cl processing chain makes use of the following auxiliary datasets:

• USGS Digital Elevation Map (USGS, 1996, described by https://doi.org/10.5066/F7GB230D)
• ERA-Interim surface and atmospheric profile temperatures and pressure (Dee et al., 2011)
• ERA-Interim profiles of moisture content and Ozone concentrations (Dee et al., 2011)
• ERA-Interim snow depth and albedo (Dee et al., 2011)
• National Snow and Ice Data Center Near-real-time Ice and Snow Extent (NISE) sea ice concentration (Brodzik and Stewart, 2016).
• ERA-Interim 10 m u and v wind components (Dee et al., 2011).
• MODIS-based land surface bidirectional reflectance distribution function (BRDF) data (MCD43C1 Collection 6, (Schaaf and Wang, 2015)).
• Land surface emissivity from the Cooperative Institute for Meteorological Satellite Studies (CIMSS) "Baseline Fit" database.
• Solar and Heliospheric Observatory (SOHO) and Solar Radiation and Climate Experiment (SORCE) incoming total solar irradiance.

For L1 data outside the temporal coverage of these datasets (for example, ATSR-2 data prior to the 1999 launch of MODIS products), climatologies based on these data are used. In the case of the SLSTR ICDR, ERA-5 data is used rather than ERA-Interim.

1.4.3 General characteristics of the product

The general characteristics of the product are given by Table 1-8.

Table 1-8: Characteristics of the Cloud_cci ERB TCDR and SLSTR ICDR

2. User Requirements

2.1 Earth Radiation Budget CERES TCDR v1.0 + ICDR v1.x (OLR, RSF)

2.1.1 Summary of target requirements (KPIs)

The accuracy requirement (here only expressed as the random component RMSD) for the CERES upward shortwave and longwave fluxes is set to 2.5 Wm^-2. Corresponding stability requirements are 0.3 Wm^-2decade^-1 and 0.2 Wm^-2decade^-1, respectively for the shortwave and longwave. The CERES team has demonstrated that the fluxes in EBAF edition 4 CDR meet these accuracy and stability requirements [D4]. These values have been adopted as KPIs for the OLR and RSF TCDR [D5].

For the ICDR period, the C3S approach is followed, using ERA5 as reference. The anomalies of global mean fluxes (RSF, OLR) with respect to ERA5 should remain within the 2.5% and 97.5% percentiles of the anomalies observed during the TCDR period (03/2000 to 10/2018). These 2.5% and 97.5% percentiles are: 0.4 W/m² and 2.3 W/m² (range of 1.9 W/m²) and -2.4 W/m² and -1.3 W/m² (range of 1.1 W/m²), respectively for the RSF and OLR.

2.1.2 Discussion of requirements with respect to GCOS and other requirements

The applied KPIs are only partly consistent with the GCOS requirements (GCOS-154 [D13] and GCOS-200 [D14]) for the ECV Earth radiation Budget [D6] in terms of accuracy and stability which are given in Table 2‑1. Indeed, while the stability KPIs are fully consistent with GCOS, the accuracy KPIs have been relaxed from 1 Wm^-2 to 2.5 Wm^-2. It is worth to mention that, in the previous release of GCOS requirements (GCOS-107, [D12]), the accuracy requirement for OLR and RSF was set at 5.0 Wm^-2. The applied KPIs are then in-between GOS-107 and GCOS-154.

Table 2‑1: GCOS requirements for OLR and RSF (GCOS-154 and GCOS-200)

2.1.3 Data format and content issues

The EBAF data are available at NASA as NetCDF CF1.4, through an OPeNDAP server. There are no known issues with the data format or content of the files. Due to technical limitations, the OPeNDAP features offered by NASA, such as subsetting or reprojection, are not yet available to CDS users.

2.2 Earth Radiation Budget HIRS OLR TCDR v1.0

2.2.1 Summary of target requirements (KPIs)

As for CERES EBAF, the Key Performance Indicator for accuracy is set to 2.5 Wm^-2 for the HIRS OLR CDR. In terms of stability, the KPI is set to 0.2 Wm^-2 decade^-1.

2.2.2 Discussion of requirements with respect to GCOS and other requirements

Table 2‑1 provides the GCOS-154 ([D13]) requirement for OLR.

As for CERES, the KPIs are only partly compliant with GCOS as the accuracy requirement has been relaxed from 1 Wm^-2 to 2.5 Wm^-2. In v02r07, the spatial resolution of the monthly mean HIRS OLR CDR is 2.5° x 2.5°, therefore not strictly compliant with the 100 km recommended by GCOS. The user requiring finer spatial resolution can consider downloading the daily mean HIRS OLR product which is provided at a 1° x 1° spatial resolution, but this product is not part of the CDS and must be downloaded from the NOAA servers.  

In terms of temporal resolution, only monthly mean is provided, without attempting to resolve the diurnal cycle.

2.2.3 Data format and content issues

The HIRS OLR CDR data is produced at the National Centers for Environmental Information (NCEI) of the U.S. National Oceanic and Atmospheric Administration (NOAA). The data is provided as a NetCDF CF1.4 file, through an OPeNDAP server. There are no known issues with the data format or content of the files. Due to technical limitations, the OPeNDAP features offered by NOAA/NCEI, such as subsetting or reprojection, are not yet available to CDS users. The HIRS OLR CDR ATBD [D8] contains a detailed description of the product format and content. The “landing page” for the HIRS OLR CDR is https://doi.org/10.7289/V5222RQP.

2.3 Earth Radiation Budget TSI TOA TCDR v2.0 + ICDR v2.x

2.3.1 Summary of target requirements (KPIs)

The Key Performance Indicators for the TCDR are:

• Accuracy requirement (here only expressed as the random component RMSD) < 1 Wm^-2.
• Stability requirement better than 0.3 Wm^-2 decade^-1

For the ICDR period, the C3S approach is followed, using modeled TSI from proxy data (see Dewitte and Nevens, 2016). The anomalies of TSI with respect to the model should remain within the 2.5% and 97.5% percentiles of the anomalies observed during the TCDR period (1^st Jan. 1979 to 31^st Dec. 2018).

2.3.2 Discussion of requirements with respect to GCOS and other requirements

Concerning the incoming solar energy, the GCOS considers 2 products as essential for the global climate: the Total Solar Irradiance (TSI) and the Solar Spectral Irradiance (SSI). The TSI is defined as the “Flux density of solar radiation at TOA (Wm^-2)” while the SSI is defined as “the solar irradiance measured as a function of wavelength (Wm^-2μm^-1)”. The GCOS requirements are given in Table 2‑2. Currently, the CDS only provides TSI data.

Table 2‑2: GCOS requirements [D14] concerning the total and spectral solar irradiance (TSI and SSI).

2.3.3 Data format and content issues

Following the standard practice in the community, the TSI timeseries is released as a simple ASCII file. The current format provides TSI values as a function of the day, and in addition, many additional fields, including the original timeseries of the various instruments used to construct the composite.

2.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR-based ICDR v3.1 (OLR,RSF)

2.4.1 Summary of target requirements (KPIs) - TCDR

The target requirements for the Cloud_cci products (Table 2-3) are defined by the WMO Global Climate Observing System (GCOS) initiative [D13], which defines and lays down targets for the observation of ECVs. It should be noted that GCOS requirements are targets for what should be achievable through Earth observation and are often not attainable using existing or historical observing systems.

Table 2‑3: Target requirements for surface radiation budget defined by GCOS-154 [D13].

The Cloud_cci product, and the SLSTR extension, achieve or exceed the frequency and resolution requirements (however, they do not resolve the diurnal cycle, , as this is not possible with a single low-Earth-orbit platform).

2.4.2 Summary of target requirements (KPIs) - ICDR

The Cloud_cci (A)ATSR products are brokered from the ESA CCI programme and cannot be altered within the scope of C3S_312b_Lot1. However, this dataset forms the basis of the KPIs for the SLSTR based ICDR going forward. The KPIs for the ERB product are based on comparison against the NASA Clouds and the Earth's Radiant Energy System (CERES) instruments. 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 2-4.

Table 2-4: Key performance indicators (KPIs) for the Cloud_cci SRB record, to be applied to the SLSTR ICDR data.

2.4.3 Discussion of requirements with respect to GCOS and other requirements

Requirements are consistent with GCOS. See Section 2.4.1.

2.4.4 Data format and content issues

The Cloud_cci v3 cloud property products are defined using standard data formats (netCDF) and map projections (regular latitude/longitude grids). Meta data definitions follow the Climate & Forecast conventions (http://cfconventions.org/).

3. Gap Analysis

3.1 Description of past, current and future satellite coverage

Quantification of the Earth Radiation Budget with broadband radiometers already has a long history. The design of the instruments included narrow (scanning) and wide (non-scanning) FOV, and instruments have been flown on both Low Earth Orbit (LEO) and geostationary (GEO) satellites. A recent review of available data is provided by Dewitte and Clerbaux (2017).

3.1.1 Earth Radiation Budget CERES TCDR v1.0 + ICDR v1.x (OLR, RSF)

CERES EBAF incorporates uninterrupted observations provided by the CERES instruments on EOS satellites since 2000 (for Terra) and 2002 (for Aqua). The data are combined with geostationary observations to mitigate the error in regions of non-standard diurnal cycle (e.g., convection). It is expected that this approach, combining one or several CERES or CERES-like broadband radiometers on LEO with GEO data of the latest generation, will be followed during the coming 10 to 15 years.

The follow-up of the CERES instrument is still to be defined, given the cancellation of the Radiation Budget Instrument (RBI). NASA is committed, however, to maintaining consistency of future instruments with the CERES record. The CERES team has estimated the probability of a data gap in the CERES record to remain below 15% until 2025 [Norman Loeb, ERB Workshop 2018]. The risk of a data gap may increase after that date, dependent on the development of the follow-up missions. To maintain continuity, NASA has issued a call for Earth Venture Continuity (EVC) for the procurement, within a limited cost envelop of 150 M$, of an instrument sharing many aspects of the CERES instrument. The instrument’s data shall be processed with the existing CERES ground segment. The proposal’s evaluation has been complete early 2020 and the selected one is called Libera (in the Roman mothology Libera is the daughter of Ceres, the goddess for agriculture). The first Libera instrument is expected to fly on the JPSS-3 satellite. The afternoon observations therefore seem to be safeguarded.

As the Terra mission has lasted well past its design lifetime and the NASA EVC only considers the afternoon orbit, there is a real risk of a data gap for the morning observations. At that time, the CERES record would then be based on afternoon observations only.

The possibility of using data from the Chinese Second Generation Polar Orbit Meteorological Satellites (FY-3 series) to ensure the continuity of the data record is still under investigation. As European contribution, a prototype processing of the FY-3 data is being developed at the RMIB with a recent version of the CERES ADMs. The Earth Radiation Measurement (ERM) instruments fly or will fly on FY-3A, FY-3B, FY-3C, FY-3E and FY-3H. The ERM-1 instrument on FY-3C is especially interesting as it provides morning observations at 10:15 ECT. The subsequent instruments will be ERM-2 on FY-3E and FY-3H which will provide observations at 06:00 ECT. This orbit is obviously less scientifically meaningful for RSF estimation.   

EarthCARE, the 9^th ESA Earth Explorer mission, is now planned for launch in March 2023. The mission includes a 3-views Broadband Radiometer (BBR) that is going to provide TOA shortwave and longwave fluxes with an unprecedented instantaneous accuracy (requirement < 10 W/m²). The EarthCARE data are not aimed to be directly ingested in generation of global CDR (the BBR swath is limited to 18km while the orbits are separated by 2574km at the Equator). However, EarthCARE BBR data presents many opportunities for improving global CDR of TOA Earth Radiation Budget. In particular, the BBR will complement future GeoRing TOA radiation products based on the latest generation of geostationary imagers (i.e. GOES ABI, Himawari AHI, and Meteosat FCI). With respect to the previous generation, these new imagers provide extended spectral coverage in the 0.4µm-0.6µm region where aerosols scattering and absorption directly affect the ERB. The EarthCARE BBR fluxes will be valuable to characterize the accuracy of these new GEO products, while the EarthCARE radiances will be valuable to homogenize the fluxes products coming from the different imagers in the GeoRing (calibration transfer).

3.1.2 Earth Radiation Budget OLR_HIRS TCDR v1.0

High-resolution Infra-Red Sounder (HIRS) instruments have been flown on a total of 18 satellites, as detailed in Table 1-4 and Table 3-1. The sounding mission is now carried out with advanced hyperspectral sounders like CrIS and IASI, and there is no more HIRS instrument on NOAA-20 and Metop-C.

Table 3-1: HIRS instrument version per satellite.

Currently, data are being acquired from the NOAA-18 and -19 (afternoon) and Metop-A and –B (morning). Although noise levels in some of the HIRS channels have been found not to meet requirements, it did not affect the generation of the CDR. The main problem to monitor in the coming years will be the drift in Equator Crossing Time (ECT) for those 4 satellites. On longer timescales, HIRS-like data from CrIS and IASI (and successors as IASI-NG) should be considered for inclusion in the CDR.

3.1.3 Earth Radiation Budget TSI TOA TCDR v2.0 + ICDR v2.x

Table 1-7 lists the main space-borne instruments for TSI observation and indicates the ones used to construct the C3S composite CDR.

Concerning the v2.x ICDR (from 1st January 2019 onward), solar irradiance data are being acquired from 2 instruments on the SOHO satellite (DIARAD/VIRGO and PMO6) and the TIM instruments on the SORCE, TCTE and TSIS-1 (on the ISS) missions. The SIM instruments on FY-3B and FY-3C are not (yet) validated enough for inclusion in the composite. Also, long-term data provision has still to be secured before inclusion of these data in an operational ICDR The European instruments on SOHO (launched in 1996!) are well beyond their expected lifetime and are expected to be discontinued soon. So, there is a significant probability that TSI observations will be provided only by the American TIM (or TIM-like) instruments in the future. This could limit our capacity to detect instrument degradation and assess CDR stability.

3.1.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR based ICDR v3.x(OLR,RSF)

The Cloud_cci v3 dataset is based on radiances provided by the ATSR series of sensors. These instruments flew on sun-synchronous polar orbiting satellites with daytime equatorial crossing times in the mid-morning; 10:30 Local Time on Descending Node (LTDN) for ATSR-2 and 10:00 LTDN for ENVISAT, with both satellites sharing the same ground track. There were 14.3 orbits per day, meaning 28 equatorial overpasses per-day, with measurements covering a total of 18% of equatorial circumference of the Earth (with equally spaced 512 km swaths). The observation frequency increased at higher latitudes (with a maximum of 14 observations per day at the poles) due to increasing overlaps between the satellite swaths. Both sensors provided the same seven channels (and used the same conical dual-viewing geometry), but not all channels were provided at all times, or at full digitization rate from ATSR-2, due to limitations of the data bandwidth provided by the ERS-2 platform. Over ocean regions, ATRS visible channels were often only provided in a 256 pixel "narrow-swath" mode. The channels provided by both instruments were centered at 0.55, 0.67, 0.87, 1.6, 3.7, 10.8, 12.0 m and the filter band passes were very similar between instruments. Despite the low-data rate modes of ATSR-2, the combination of the very similar instrument specifications, very close orbital parameters and the lack of any significant orbital drift in the ERS-2 and ENVISAT satellites mean that ATSR-2 and AATSR provide a highly consistent data record.

The TCDR from Cloud_cci v3 begins with the launch of ERS-2 in mid-1995 and continues until the failure of ENVISAT in April 2012. Due to instrument problems, there is a six-month data gap in the ATSR-2 record from January to June 1996.

There is an overlap of 1 year of data between the ATSR-2 and AATSR platforms, between mid-2002 (when ENVISAT was launched) and mid-2003 (when the onboard data storage on ERS-2 failed). There is additional ATSR-2 data available up-to 2009, but this is not global as data could only be collected when the satellite was within line-of-sight with a ground receiving station, and has not been included in the TCDR. There is some scope to push the coverage of the ATSR cloud record back to 1991, by using the ATSR-1 instrument (onboard ERS-1), which also flew in a similar orbit to its successors. However, ATSR-1 lacked the shortwave channels (apart from the 1.6 m) channel, which would reduce the information available in daylight retrievals, as well as the estimation of shortwave radiative fluxes, and would represent a significant inhomogeneity in the TCDR.

The extension of the ATSR TCDR makes use of SLSTR sensors onboard the Sentinel-3 platform. SLSTR represents a significant upgrade over (A)ATSR, providing a wider swath, two satellites within interleaved orbit swaths, additional channels and an operational system for near realtime acquisition of data. The Sentinel-3s have a very similar orbit to ENVISAT and the ERS satellites, with a sun-synchronous orbit with an LTDN of 10:00, and 14.3 orbits per-day. However, there just over a 4-year gap between the end of the AATSR record and the first SLSTR data. There are several options available to fill this gap, as ORAC can be applied to most radiometers with similar channels to those provided by ATSR. Indeed, cloud CDRs of ORAC applied to both MODIS and AVHRR already exist, having been produced in the Cloud_cci program, but have not been brokered to the CDS.
It should also be noted that ORAC could also be applied to the VIIRS and MetImage instruments, which could complement the SLSTR ICDR.

3.2 Development of processing algorithms

3.2.1 Earth Radiation Budget CERES TCDR v1.0 and ICDR v1.x (OLR, RSF)

Generally speaking, the processing of CERES data in the EBAF CDR is of excellent quality, and, in recent editions, fully exploits the advanced angular sampling capabilities of the instrument. The quality of the fluxes in some particular regions and/or conditions could benefit from further improvements; e.g., cloud retrieval over Polar Regions. Efforts are being made in this direction and improvements in the CERES data processing can be expected in the coming years. The record will also benefit from improved ancillary data (in particular the NWP fields from the latest reanalysis), the homogeneity of the MODIS radiance used for the cloud retrieval, and use of the Fundamental Climate Data Record (FCDR) from GEO satellite observations needed for the TISA.

For some instruments, like the ERM on FY-3 or ScaRaB on Megha-Tropiques, the science processing sometimes relies on outdated angular dependency models, and there is likely a need to improve the algorithms before incorporation in any future CDR.
All broadband radiometers exhibit some form of degradation when in space. This degradation has a spectral dimension, and the temporal decrease of the signal is strongly scene dependent. Based only on the on-board calibration devices, this degradation is difficult to assess and efforts to model the change in spectral response of the detectors and optics should be pursued.

Finally, in EBAF, the closure of the Earth radiative budget depends on an assessment of ocean heat content. Given recent developments in this field, consolidation of the ocean heat content trend is to be expected in the coming years, with a direct bearing on the top-of-atmosphere fluxes.

3.2.2 Earth Radiation Budget OLR HIRS TCDR v1.0

Due to discontinuation of the HIRS instruments from NOAA-20 and Metop-C onward, developments would be necessary to continue the record based on HIRS-like data from the Infrared Atmospheric Sounding Interferometer (IASI) and Cross-track Infrared Sounder (CrIS) instruments. These developments are ongoing at University of Maryland (PI of the HIRS OLR CDR).

The currently brokered OLR products from HIRS are the monthly mean produced by NCEI/NOAA at a spatial resolution of 2.5°x2.5°. This (coarse) spatial resolution seems to be motivated by continuation of the OLR operational record that started a long time ago and is widely used. Since several years, daily mean OLR from HIRS are also available at a finer resolution of 1°x1°. In the future, these daily mean products could be aggregated to provide monthly mean data at 1°x1° resolution, consistently with the CERES EBAF record.

3.2.3 Earth Radiation Budget TSI TOA TCDR v2.0 + ICDR v2.x

The most recent improvements in the processing of data from differential absolute radiometers concern the modeling of diffraction inside the precision aperture and, for DIARAD/VIRGO, a better account of the instrument non-linearity.

Currently, there are concerns about the instrument aging more rapidly than implied by the stated stability. For instance, Dewitte and Nevens (2016) suspected some drift in the TIM/SORCE timeseries. If this is confirmed, better accounting for aging should be implemented in future releases of the CDR. The difficulty here is obviously to find a good reference to assess the aging. Having an instrument on the ISS (e.g. TIM on TSIS-1) provides the opportunity for instrument ground recalibration at the end of the operational mission.

3.2.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR-based ICDR v3.x (OLR,RSF)

The stability and quality of the input data is the key parameter which influences the reliability of the Cloud_cci v3 CDRs. The (A)ATSR TCDR is based on version 3 of the "AATSR multimission archive" maintained by CEDA and the UK National Earth Observation Data Centre (NEODC). This record incorporates the latest calibration corrections (including long-term drift corrections from vicarious calibration) and represents the most consistent and accurate record of radiances from the (A)ATSR record. A future update to this record would make a reprocessing of the Cloud_cci TCDR possible.

In the case of the SLSTR ICDR, the status of the level 1 radiances is considerably less stable. Data from early in the SLSTR record has considerably worse calibration and geolocation than recent data. When a fully reprocessed version of the data record becomes available in the future, regeneration of the cloud ICDR would be possible.
EUMETSAT has provided updated calibration corrections to SLSTR shortwave channels, communicated through the Sentinel-3 Scientific Validation Team (S3VT), which have been applied retrospectively. However, there is not yet any information on the stability of the SLSTR calibration over time.

Adaptions of the ORAC scheme to better exploit SLSTR

As mentioned above, SLSTR provides some additional channels over the earlier AATSR instruments. Of particular note is the new 1.3 μm channel, which, due to its location in a water-vapour absorption feature, it particularly sensitive to the presence of high-altitude clouds. Utilizing this channel in the retrieval scheme itself is unlikely to be beneficial, as accurate knowledge of the water vapour profile is needed to accurately model the radiances. However, the use of this channel in prior cloud-detection and characterization is to be investigated in coming Cloud_cci+ work.

Forward model improvements

Further improvements to the forward modelling of clouds for the ORAC retrieval scheme are also underway. In particular:

• The SLSTR ICDR makes use of ERA-5, rather than the ERA-Interim used for the TCDR.
• The spectral dependence of cloud scattering and absorption will be modelled across the bandpass of the instrument channels (rather than at the channel centre as previously).
• At present cloud is modelled as an infinitesimally thin layer within an atmosphere modelled by RTTOV. The modelling of cloud geometric thickness effects will also be investigated in the upcoming Cloud_cci+ project.
• The use of new ice cloud optical properties will also be investigated, as these become available.
• Improvements in the propagation of uncertainty from L2 products to gridded L3 products is also under investigation.

3.3 Methods for estimating uncertainties

3.3.1 Earth Radiation Budget CERES TCDR v1.0 + ICDR v1.x (OLR, RSF)

The CERES team has invested a considerable effort in the validation of the EBAF record. A summary of the findings is in the Data Quality Summary (DQS) for EBAF edition 4 [D4]. Overall, the stability of the CERES EBAF product complies with the GCOS requirements. In terms of accuracy, uncertainties are 2.5 W m^-2 for SW and LW. Stability is not easy to demonstrate at the 0.3 W m^-2 decade^-1 level and in Dewitte et al. (2019) slightly out of requirement aging is reported, but the CERES team did not fully agree with the methodology followed in this work. If anything, this demonstrates the lack of consensus w.r.t. the methodologies to assess ERB CDR stability.

3.3.2 Earth Radiation Budget HIRS OLR TCDR v1.0

The product has been intensively evaluated by Dr. Hai-Tien Lee from University of Maryland (UMD), the PI of the HIRS OLR product. The results are summarized in the “Quality Assurance Results and Summary” document [D11], available at:

 http://olr.umd.edu/References/QA_Summary_OLR-Monthly_and_Daily_CDR_20180831.pdf

The best reference datasets for the validation of the HIRS OLR CDR are the CERES EBAF and CERES SYN1deg-month products. The validation is then restricted to the 2000-onward period (with slightly lower quality before the inclusion of CERES Aqua in 2002).

Efforts to validate the CDR accuracy and stability in the pre-CERES era remain very relevant. Stability might have been affected by HIRS instrument degradation but also from the significant changes in the ECT of the NOAA satellites. Intercomparisons with atmospheric reanalysis provide some insight on the CDR stability. Such intercomparisons could be a piece of the puzzle but, alone, are not accurate enough to address the stability at the 0.2 W m^-2 decade^-1 level.

In [D10], an intercomparison is performed between HIRS OLR, CERES EBAF and the CM SAF GERB/SEVIRI data records following the Triple Collocation (TC) methodology. Assuming that the errors affecting those 3 records are uncorrelated, it is possible to estimate the individual error for the 3 CDRs. Further assessment on the applicability of the TC methodology to ERB datasets would be highly beneficial to narrow the uncertainty estimate.

3.3.3 Earth Radiation Budget TSI TOA TCDR v2.0 + ICDR v2.x

A first indicator of the uncertainty is the comparison of the individual TSI time series, before they are combined in the composite TSI timeseries. This is done routinely, as part of the CDR generation. These intercomparisons permit the identification of periods of lower quality (e.g. drift) for some of the individual TSI instruments. These periods have been discarded from the final C3S composite (Dewitte and Nevens, 2016).

Uncertainty and stability can also be assessed, to a certain level, using a proxy for the TSI like the number of Sun spots or indices extracted from magnetograms. Efforts in this direction will not only narrow the uncertainty estimate for the TSI CDR, but also permit to extend back in time the CDR in the pre-satellite era.

3.3.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR-based ICDR v3.x (OLR,RSF)

The ORAC retrieval scheme provides propagated uncertainties on the retrieved cloud parameters, but these are not propagated through the broadband flux calculations at present. Thus, no uncertainty estimates are provided in the (A)ATSR TCDR or SLSTR ICDR products, aside from the standard deviation of the level-2 pixels included in each monthly-mean grid box. Thus, uncertainty information is only available through validation activities.

3.4 Opportunities to improve quality and fitness-for-purpose of the CDRs

3.4.1 Earth Radiation Budget CERES TCDR v1.0 + ICDR v1.x (OLR, RSF)

Currently there is no indication of significant limitations with the data that would call for a reprocessing of the EBAF record in the coming months. We keep in touch with the CERES Science Team through attendance to the bi-annual science team meetings, where the Edition 5 of the data will be decided. CERES Edition 5 is not expected to either drastically improve the current EBAF record nor to enhance significantly its fitness-for-purpose.

3.4.2 Earth Radiation Budget OLR HIRS TCDR v1.0

The current version of the CDR is based on 4 HIRS channels and on the geostationary IR observations via GridSat (Knapp et al., 2011). Several opportunities have been identified for improvement of the record as detailed in [D7]. Here, the following opportunities for European contributions can be considered:

• Use true FCDR for the HIRS radiances, e.g. the FCDR developed in the frame of the Fidelity and uncertainty in climate data records from Earth Observations (FIDUCEO) Horizon 2020 project.
• Merge with high spatial resolution data from AVHRR, e.g. also based on an FCDR of AVHRR channel 4 and 5 observations from FIDUCEO.
• Another potential European contribution could be a merging of the HIRS OLR CDR with the CM SAF AVHRR OLR CDR (foreseen for release in 2021 as part of CM SAF CLARA-A3 CDR).

3.4.3 Earth Radiation Budget TSI TOA TCDR v2.0 + ICDR v2.x

The question of the absolute level of the TSI timeseries is still partly unresolved. Different instruments have shown differences that exceeded the sum of their stated individual accuracies. Solving this problem would require an even more comprehensive and accurate instrument ground characterization of the instruments, fully linked to international metrology standards, and, if possible, on re-characterization at the end of the mission (e.g. for instrument on the ISS or space shuttles). On ground intercomparison campaigns of space instruments, as was organized at the World Radiation Center at PMO/Davos, also help to understand remaining differences in absolute level.

3.4.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR-based ICDR v3.x (OLR,RSF)

Most potential improvements to ORAC radiative flux products stem from improvements to the underlying cloud retrieval scheme, which are discussed below.

The planned development of the ORAC retrieval scheme, as applied to (A)ATSR and SLSTR, has already been described in section 3.2.4. ORAC is under active development, both through the ESA CCI+ program and through national UK funding (in particular, under the National Centre for Earth Observation). New improvements of the scheme, where applicable, will be fed through to the production of improved CDR products from SLSTR.

It is also worth noting that the ORAC scheme is not specifically designed for application to (A)ATSR or SLSTR. CDRs have already been produced using the scheme for the AVHRR and MODIS instruments, under previous iterations of the CCI program. The scheme has also been applied to geo-stationary sensors (SEVIRI, GOES and Himawari-AHI), and improved application of the scheme to SEVIRI in particular (making use of the water-vapor sounding channels provided by the instrument) is being undertaken in CCI+.

The code includes the ability to utilize sounding channels (CO₂ slicing and water-vapor absorption), as well as a multi-layer cloud retrieval mode [D18], which greatly improve on the shortcomings of the existing “heritage channel” (AVHRR-like) CDRs produced in CCI, and retrieves the properties of dual-layer cloud scenes. Thus, the scheme provides the scope for the production of cutting-edge CDRs from a wide range of instruments, all with a consistent retrieval approach.

3.5 Scientific Research needs

3.5.1 Earth Radiation Budget CERES TCDR v1.0 + ICDR v1.x (OLR, RSF)

In view of a likely gap in the morning broadband observation at the end of the Terra mission, it can be recommended that European players (from instance EUMETSAT, or the GERB and ScaRaB teams) develop ERB products for the Metop or Metop-SG satellites. In particular, Metop-SG will embark the Multi-viewing, -channel, -polarisation Imaging (3MI) instrument that could be valuable for the shortwave flux estimation. The development of TOA radiation fluxes for the MetImage instruments is also very relevant at this level, especially for the RSF.

3.5.2 Earth Radiation Budget OLR HIRS TCDR v1.0

As already stated, the main effort should be on the generation of FCDR for the HIRS observation record (e.g. through FIDUCEO).

New reanalysis systems, incorporating the radiative effect of the main volcanic eruptions, could be used to assess the uncertainty of the HIRS OLR CDR during the pre-CERES era. This would provide further evidence that the effect of ECT drift of the NOAA satellites (and also of the Metop satellites toward end of life) is accurately compensated for in the processing. For example, a difference in global mean OLR between the HIRS OLR CDR and the OLR in the ERA5 reanalysis has been found. Also, variation of the bias appears to be larger in the first half of the record wrt the second half.

Further research in applicability of the Triple Collocation (TC) methodology to ERB datasets is also needed.

3.5.3 Earth Radiation Budget TSI TOA TCDR v2.0 + ICDR v2.x

Scientific research should focus on a better exploitation of proxy data for solar activity (sun spot number, magnetic indices …). Improved proxy data would permit a better detection of instrumental aging and detection of erroneous data, leading to improved TSI composite.

3.5.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR-based ICDR (OLR,RSF)

As mentioned above, most improvements to ORAC radiative products will come from improvements in the underlying cloud retrieval performance. One of the largest sources of uncertainty in cloud (and aerosol) products has always been and continues to be the problem of "scene identification"; i.e. distinguishing cloud from clear-sky or elevated aerosol loading over all surface types, as well as identifying cloud type (liquid, ice, multi-layer etc). Areas known to be particularly problematic include identifying cloud over ice/snow surfaces, dealing with the so-called twilight zone between cloudy and clear pixels and the correct identification and classification of extreme aerosol events (such as dust storms, smoke plumes and volcanic ash). Much work is ongoing, particularly in the field of machine learning, on addressing this area.

As with most products centered on Earth radiative processing, improvements in the knowledge of, and updates to databases of surface properties, particularly land-surface reflectance and emissivity are key.

3.6 Opportunities from exploiting the Sentinels and any other relevant satellite

3.6.1 Earth Radiation Budget CERES TCDR v1.0 + ICDR v1.x (OLR, RSF)

The future launch of the European/Japanese EarthCARE satellite (with a 3-views BBR instrument) will also be an opportunity to better characterize the error in the CERES products. Some matches can be expected between the 14:00 descending orbit of EarthCARE and the 13:30 ascending orbit of the EOS Aqua satellite. This is foreseen in two calibration and validation (Cal/Val) research activities selected by ESA. The first Cal/Val activity will be done by the CERES team at NASA Langley Research Center (LaRC), while a second activity will be conducted by a consortium including RMIB, Imperial College London and NASA LaRC.

Implementation of TOA radiation products from the improved geostationary imagers (GOES ABI, Himawari AHI, MTG/FCI) presents also many opportunities of synergy with the CERES CDR. Activities toward ERB GeoRing are foreseen in the Continuous Development and Operation Phase 4 (CDOP 4) of CM SAF (2022-2027).

In the more distant future, measurements of reflected shortwave flux (from CERES or other missions) are expected to benefit from metrology missions like the Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS). This mission was selected in November 2019 for funding within the Earth Observation Earth Watch programme. It will provide state of the art and fully SI-traceable measurements of the incoming and outgoing solar radiation, with an unprecedented accuracy thanks to innovative calibration devices. The mission, led by the National Physical Laboratory in the UK, is currently in phase A/B.

3.6.2 Earth Radiation Budget OLR HIRS TCDR v1.0

The Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission has been selected for implementation as the 9^th ESA Earth Explorer. FORUM will sample the infrared spectrum from 100 cm^-1 to 1600 cm^-1 (100 µm to 6.25 µm) with a spectral resolution of 0.5 cm^-1. Combined with IASI-NG, this mission will provide accurate spectral measurement of the infra-red spectrum. This kind of spectrum would be interesting to understand the limits of the HIRS channels for OLR estimation through narrowband-to-broadband conversion.

3.6.3 Earth Radiation Budget TSI_TOA TCDR v2.0 + ICDR v2.x

The TSIS-1 mission includes a TIM instrument on the International Space Station (ISS). A second instrument is foreseen as a TSIS-2 mission which is currently planned for launch in 2023. The opportunity to recalibrate these instruments once they are back on Earth will be valuable to better quantify aging and degradation in space for this kind of radiometer.

3.6.4 Earth Radiation Budget ESA_CCI_AATSR TCDR v3.0 + SLSTR-based ICDR v3.x (OLR,RSF)

The ESA SLSTR v3.x ICDR directly exploits data from the Sentinel-3 platform. There have been examples shown of utilizing Sentinel-3 OLCI-like measurements (mainly using MERIS on ENVISAT) for cloud retrieval in conjunction with (A)ATSR or SLSTR (Carbajal Henken et al. 2014), but difficulties in cross-calibration and co-registration of the different instruments have meant these products have not shown improved performance over the (A)ATSR/SLSTR only algorithms. The availability of a well co-located and calibrated joint SLSTR-OLCI L1 product, could resurrect this approach to further improve cloud products derived from Sentinel-3 (and the preceding ENVISAT).

As discussed in section 3.1.4, the ORAC retrieval scheme can be, and has been, applied to a wide range of satellite visible-IR imaging radiometers. A particular instrument, of direct relevance to the Sentinel satellite program is the Flexible Combined Imager (FCI) to fly on MeteoSat Third Generation/Sentinel-4. This instrument is essentially a replacement for the SEVIRI sensors on MSG, with capabilities similar to those provided by Himawari-AHI and GOES-ABI imagers (which ORAC has already been applied to).

References

Brodzik, M. J. and J. S. Stewart. 2016. Near-Real-Time SSM/I-SSMIS EASE-Grid Daily Global Ice Concentration and Snow Extent, Version 5. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/3KB2JPLFPK3R.

Carbajal Henken, C.K., R. Lindstrot, R. Preusker and J. Fischer, 2014: FAME-C: cloud property retrieval using synergistic AATSR and MERIS observations. Atmos. Meas. Tech., 7, 3873–3890, doi:10.5194/amt-7-3873-2014.

Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A. C. M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J., Haimberger, L., Healy, S. B., Hersbach, H., Hólm, E. V., Isaksen, L., Kållberg, P., Köhler, M., Matricardi, M., McNally, A. P., Monge-Sanz, B. M., Morcrette, J.-J., Park, B.-K., Peubey, C., de Rosnay, P., Tavolato, C., Thépaut, J.-N., Vitart, F., 2011: The ERA-Interim reanalysis: configuration and performance of the data assimilation system, Quarterly Journal of the Royal Meteorological Society, 137, 656, (doi = 10.1002/qj.828), 553—597.

Dewitte, S. and S. Nevens, 2016: The total solar irradiance climate data record. The Astrophysical Journal, 830(1), p.25.

Dewitte S. and N. Clerbaux, 2017: Measurement of the Earth Radiation Budget at the Top of the Atmosphere — A Review, Remote Sensing, 9, 1143; doi:10.3390/rs9111143.

Dewitte, S., N. Clerbaux, N. and J. Cornelis, 2019: Decadal Changes of the Reflected Solar Radiation and the Earth Energy Imbalance. Remote Sensing, 11(6), p.663.

Doelling, D. R. et al., 2013: Geostationary enhanced temporal interpolation for CERES flux products. Journal of Atmospheric and Oceanic Technology, 30(6), 1072-1090.

Doelling, D.R., et al., 2016. Advances in geostationary-derived longwave fluxes for the CERES synoptic (SYN1deg) product. Journal of Atmospheric and Oceanic Technology, 33(3), pp.503-521.

Harries, J.E. et al., 2005: The Geostationary Earth Radiation Budget Project, Bulletin of American Meteorological Society, 86(7), 945-960, doi:10.1175/BAMS-86-7-945.

Knapp, K.R., et al., 2011. Globally gridded satellite observations for climate studies. Bulletin of the American Meteorological Society, 92(7), pp.893-907.

Lee, H.-T., 2014: Daily OLR CDR – Development and Evaluation. CERES Science Team Meeting, Apr 2014.

Lee, H.-T., 2014: Daily OLR Climate Data Record. EGU General Assembly, Apr 2014.

Lee, H.-T., C. J. Schreck, and K. R. Knapp, 2014: Generation of Daily OLR CDR. Eumetsat Meteorological Satellite Conference, Sep 2014.

Lee, H.-T., 2018: Quality Assurance Summary and Results for Monthly and Daily OLR CDR (rev.20180831).

Lee, H.-T., A. Gruber, R. G. Ellingson and I. Laszlo, 2007: Development of the HIRS Outgoing Longwave Radiation climate data set. J. Atmos. Ocean. Tech., 24, 2029–2047.

Loeb, N. G., S. Kato, and B. A. Wielicki, 2002: Defining top-of-atmosphere flux reference level for Earth Radiation Budget studies. Journal of Climate, 15, 3301-3309.

Loeb, N. G., et al., 2009: Toward optimal closure of the Earth's top-of-atmosphere radiation budget. Journal of Climate, 22(3), 748-766.

Loeb, N. G., et al., 2018: Clouds and the earth's radiant energy system (CERES) energy balanced and filled (EBAF) top-of-atmosphere (TOA) edition-4.0 data product. Journal of Climate, 31(2), 895-918.

McGarragh, G. R., Poulsen, C. A., Thomas, G. E., Povey, A. C., Sus, O., Stapelberg, S., Schlundt, C., Proud, S., Christensen, M. W., Stengel, M., Hollmann, R., and Grainger, R. G., 2018: The Community Cloud retrieval for CLimate (CC4CL) – Part 2: The optimal estimation approach, Atmos. Meas. Tech., 11, 3397–3431, https://doi.org/10.5194/amt-11-3397-2018.

Minnis P., et al., 2011: CERES Edition-2 cloud property retrievals using TRMM VIRS and Terra and Aqua MODIS data--Part I: Algorithms. IEEE Trans. Geosci. Remote Sens., 49, 4374-4400.

Schaaf, C. and Wang, Z., 2015: MCD43C1 MODIS/Terra+Aqua BRDF/AlbedoModel Parameters Daily L3 Global 0.05Deg CMG V006, NASA EOSDIS Land Processes DAAC, https://doi.org/10.5067/MODIS/MCD43C1.006.

Schreck, C. J., H.-T. Lee and K. Knapp, 2018: HIRS Outgoing Longwave Radiation—Daily Climate Data Record: Application toward Identifying Tropical Subseasonal Variability. Remote Sens. 2018, 10, 1325

Smith, D., C. Mutlow, J. Delderfield, B. Watkins and G. Mason, 2012: ATSR infrared radiometric calibration and in-orbit performance. Remote Sens. Environ., 116, 4-16, DOI: 10.1016/j.rse.2011.01.027.

Sus, O., Stengel, M., Stapelberg, S., McGarragh, G., Poulsen, C., Povey, A. C., Schlundt, C., Thomas, G., Christensen, M., Proud, S., Jerg, M., Grainger, R., and Hollmann, R., 2018: The Community Cloud retrieval for CLimate (CC4CL) – Part 1: A framework applied to multiple satellite imaging sensors, Atmos. Meas. Tech., 11, 3373–3396, https://doi.org/10.5194/amt-11-3373-2018.

Wielicki, B. A., Barkstrom, B. R., Harrison, E. F., Lee III, R. B., Smith, G. L., & Cooper, J. E., 1996: Clouds and the Earth's Radiant Energy System (CERES): An earth observing system experiment. Bulletin of the American Meteorological Society, 77(5), 853-868.

Related articles

• Page:
  ECV - Glaciers, Ice Sheets, Lakes, Soil Moisture
• Page:
  IV Version 1.2; SEC Version 2.0; GMB Version 2.0: Product User Guide Specification (PUGS)
• Page:
  IV Version 1.2; SEC Version 2.0; GMB Version 2.0: System Quality Assurance Document (SQAD)
• Page:
  IV Version 1.2; SEC Version 2.0; GMB Version 2.0: Product Quality Assurance Document (PQAD)
• Page:
  IV Version 1.2; SEC Version 2.0; GMB Version 2.0: Product Quality Assessment Report (PQAR)