Solar Irradiance is the key energy input to Earth. A positive Earth Energy Imbalance (EEI) is the energy, which is continuously stored by the Earth and will ultimately be released to the atmosphere, causing global warming. In order to determine its exact value both the Total Solar Irradiance (TSI) and the Top of the Atmosphere (ToA) Outgoing Radiation (TOR) need to be measured with unprecedented accuracy and precision. However, so far, the EEI could not be determined as the measurements were not sufficiently accurate. This calls for improved instrument technologies as well as a traceable calibration chain of the space instrumentation. In this session we invite contributions on the both the measurement of solar irradiance as well as the Earth outgoing radiation which ultimately aim to pave the way to determine EEI from space.

Co-organized by CL5.1
Convener: Margit Haberreiter | Co-conveners: W. H. Swartz, Ping Zhu
vPICO presentations
| Thu, 29 Apr, 11:45–12:30 (CEST)

Session assets

Session materials

vPICO presentations: Thu, 29 Apr

Chairpersons: W. H. Swartz, Ping Zhu
Karina von Schuckmann

Human-induced atmospheric composition changes cause a radiative imbalance at the top of the atmosphere which is driving global warming. This simple number, the Earth energy imbalance (EEI), is the most fundamental metric that the scientific community and public must be aware of as the measure of how well the world is doing in the task of bringing climate change under control. Combining multiple measurements and approaches in an optimal way holds considerable promise for estimating EEI and continued quantification and reduced uncertainties can be best achieved through the maintenance of the current global climate observing system, its extension into areas of gaps in the sampling, advance on instrumental limitations, and the establishment of an international framework for concerted multidisciplinary research effort. This talk will provide an overview on the different approaches and their challenges for estimating the EEI. A particular emphasis will be drawn on the heat gain of the Earth system over the past half of a century – and particularly how much and where the heat is distributed – which is fundamental to understanding how this affects warming ocean, atmosphere and land; rising surface temperature; sea level; and loss of grounded and floating ice, which are critical concerns for society.


How to cite: von Schuckmann, K.: The Earth energy imbalance – new advances and remaining challenges, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9707,, 2021.

Peter Pilewskie and Maria Hakuba and the Libera Science Team

The NASA Libera Mission, named for the daughter of Ceres in Roman mythology, will provide continuity of the Clouds and the Earth’s Radiant Energy System (CERES) Earth radiation budget (ERB) observations from space. Libera’s  attributes enable a seamless extension of the ERB climate data record. Libera will acquire integrated radiance over the CERES FM6-heritage broad spectral bands in the shortwave (0.3 to 5 μm), longwave (5 to 50 μm) and total (0.3 to beyond 100 μm) and adds a split-shortwave band (0.7 to 5 μm) to provide deeper insight into shortwave energy deposition. Libera leverages advanced detector technologies using vertically aligned black-carbon nanotubes with closed-loop electrical substitution radiometry to achieve radiometric uncertainty of approximately 0.2%. Libera will also employ a wide field-of-view camera to provide scene context and explore pathways for separating future ERB missions from complex imagers.

The Libera science objectives associated with continuity and extension of the ERB data record are to identify and quantify processes responsible for ERB variability on various time scales. Beyond data continuity, Libera’s new and enhanced observational capabilities will advance our understanding of spatiotemporal variations of radiative energy flow in the visible and and near-infrared spectral regions. They will also enable the rapid development of angular distribution models to facilitate near-IR and visible radiance-to-irradiance conversion.

How to cite: Pilewskie, P. and Hakuba, M. and the Libera Science Team: Libera and Continuity of the Earth Radiation Budget Climate Data Record, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13183,, 2021.

Simonne Guilbert, Frédéric Parol, Céline Cornet, Nicolas Ferlay, and François Thieuleux

Radiative Budget, essential to the monitoring of climate change, can be investigated with ERB-dedicated instruments like the Clouds and the Earth Radiant Energy System (CERES) instrument (Wielicki, 1996). On the other side, non-dedicated instruments, such as POLDER-3/PARASOL measuring narrowband radiances, can also be used advantageously to obtain shortwave albedos and fluxes (Buriez et al, 2007; Viollier et al, 2002).

We present here a comparison between the shortwave fluxes and albedos derived from POLDER-3 and those derived from CERES flying aboard Aqua, chosen as a reference.

Monthly means of shortwave fluxes computed from the measurements of the two instruments are first set side by side. They show a good agreement in the all-sky case. However, after December 2009, the values from POLDER-3 display a slight drift which coincides with the lowering of the orbit of the PARASOL satellite and the modification of its overpass time in comparison to the other satellites of the A-Train mission. In clear sky situations, greater differences between POLDER and CERES shortwave fluxes are observed, especially over land regions, and the drift increases faster after 2009.

A second comparison is presented, between instantaneous albedos. For the period of coincident observations between POLDER-3 and CERES/Aqua, there is a good correlation between both products. This correlation deteriorates when the comparison is extended after 2009, as the values given by POLDER-3 increase. This result is expected, as the albedo is a function of the Solar Zenith Angle.

The slope of the increase of instantaneous albedo values is higher than for the diurnally extrapolated, monthly averaged shortwave fluxes. This tends to show that the POLDER algorithm leading to the monthly means of diurnal shortwave albedos moderates the increase of instantaneous shortwave albedo values but it doesn’t completely compensate for the effects of the drift of the instrument.


How to cite: Guilbert, S., Parol, F., Cornet, C., Ferlay, N., and Thieuleux, F.: Comparison Between POLDER/PARASOL and CERES/AQUA Shortwave Fluxes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9579,, 2021.

Duo Wu, Ping Zhu, Wei Fang, Xin Ye, Kai Wang, Ruidong Jia, Zhiwei Xia, Dongjun Yang, and Cong Zhao

A space based relative radiometer has been developed and applied to the PICARD mission. It has successfully measured 37 months solar radiation, terrestrial outgoing radiation, and a comparable interannual variation in Earth Radiation Budget (ERB) is inferred from those measurements [1]. However, since the BOS (Bolometric Oscillation Sensor [2]) relative radiometer is originally designed to measure the solar irradiance with 10 seconds high cadence comparing to the absolute radiometer. The high dynamic range of BOS limits its performance to track the Earth’s outgoing radiation in terms of instantaneous field-of-view (iFOV) and the absolute radiation level. Two relative radiometers (RR) will be developed for JTSIM/FY-3F. One is the solar channel relative radiometer aimed to measure the solar irradiance side by side with the cavity solar irradiance absolute radiometer (SIAR). The second RR is acting as a non-scanner instrument to measure the Earth’s outgoing radiation. Comparing to the design of PICRD-BOS. Each RR has included an aperture, for the solar channel it limits its Unobstructed Field of View (UFOV) to about 1.5 degree and for the Earth channel to about 110 degrees, respectively. We also test the possibility to use the Carbon Nanotube coating on the main detector. In this presentation, the design of the earth channel relative radiometer (ERR) will be introduced, including the aperture design, dynamic range and the active temperature control system. The preliminary laboratory test result of the ERR will be discussed in the end.

[1] P. Zhu, M. Wild, M. van Ruymbeke, G. Thuillier, M. Meftah, and Ö. Karatekin. Interannual variation of global net radiation flux as measured from space. J. Geophys. Res. doi:10.1002/2015JD024112, 121:6877–6891, 2016.

[2] P. Zhu, M.van Ruymbeke, Ö. Karatekin, J.-P.Noël, G. Thuillier, S. Dewitte, A. Chevalier, C. Conscience, E. Janssen, M. Meftah, and A. Irbah. A high dynamic radiation measurement instrument: the bolometric oscillation sensor (bos). Geosci. Instrum. Method. Data Syst., 4,89-98,:doi:10.5194/gi–4–89–2015, 2015.

Acknowledgement: this work is partly supported by the National Natural Science Foundation of China No. 41974207 and CSC Scholarship No.202004910181


How to cite: Wu, D., Zhu, P., Fang, W., Ye, X., Wang, K., Jia, R., Xia, Z., Yang, D., and Zhao, C.: Preliminary results of relative radiometer to measure the Earth’s outgoing radiation on FY-3F satellite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5980,, 2021.

Martin Snow, Stephane Beland, Odele Coddington, Steven Penton, and Don Woodraska

The GOES-R series of satellites includes a redesigned instrument for solar spectral irradiance: the Extreme ultraviolet and X-ray Irradiance Sensor (EXIS).  Our team will be using a high-cadence broadband visible light diode to construct a proxy for Total Solar Irradiance (TSI).  This will have two advantages over the existing TSI measurements:  measurements are taken at 4 Hz, so the cadence of our TSI proxy is likely faster than any existing applications, and the observations are taken from geostationary orbit, so the time series of measurements is virtually uninterrupted.  Calibration of the diode measurements will still rely on the standard TSI composites.  

The other measurement from EXIS that will be used is the Magnesium II core-to-wing ratio.  The MgII index is a proxy for chromospheric activity, and is measured by EXIS every 3 seconds.  The combination of the two proxies can be used to generate a model of the full solar spectrum similar to the NRLSSI2 empirical model.

We are in the first year of a three-year grant to develop the TSI proxy and the SSI model, so only very preliminary findings will be discussed in this presentation.

How to cite: Snow, M., Beland, S., Coddington, O., Penton, S., and Woodraska, D.: GOES High cadence Operational Total Irradiance: planned data products, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10348,, 2021.

Jean-Philippe Montillet, Wolfgang Finsterle, Werner Schmutz, Margit Haberreiter, and Rok Sikonja

Since the late 70’s, successive satellite missions have been monitoring the sun’s activity, recording total solar irradiance observations. These measurements are important to estimate the Earth’s energy imbalance, i.e. the difference of energy absorbed and emitted by our planet. Climate modelers need the solar forcing time series in their models in order to study the influence of the Sun on the Earth’s climate. With this amount of TSI data, solar irradiance reconstruction models  can be better validated which can also improve studies looking at past climate reconstructions (e.g., Maunder minimum). Various algorithms have been proposed in the last decade to merge the various TSI measurements over the 40 years of recording period. We have developed a new statistical algorithm based on data fusion.  The stochastic noise processes of the measurements are modeled via a dual kernel including white and coloured noise.  We show our first results and compare it with previous releases (PMOD,ACRIM, ... ). 

How to cite: Montillet, J.-P., Finsterle, W., Schmutz, W., Haberreiter, M., and Sikonja, R.: Data Fusion of Total Solar Irradiance Composite Time Series Using 40 years of Satellite Measurements: First Results  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4382,, 2021.

Odele Coddington, Erik Richard, Dave Harber, Peter Pilewskie, Tom Woods, Kelly Chance, Xiong Liu, and Kang Sun

Recently, we incorporated our new understanding of the absolute scale of the solar spectrum as measured by the Spectral Irradiance Monitor (SIM) on the Total and Spectral Solar Irradiance Sensor (TSIS-1) mission and the Compact SIM (CSIM) flight demonstration into a solar irradiance reference spectrum representing solar minimum conditions between solar cycles 24 and 25. This new reference spectrum, called the TSIS-1 Hybrid Solar Reference Spectrum (HSRS), is developed by re-normalizing independent, very high spectral resolution datasets to the TSIS-1 SIM absolute irradiance scale. The high-resolution data are from the Airforce Geophysical Laboratory (AFGL), the Quality Assurance of Ultraviolet Measurements In Europe (QASUME) campaign, the Kitt Peak National Observatory (KPNO) and the Jet Propulsion Laboratory’s (JPL) Solar Pseudo-Transmittance Spectrum (SPTS). The TSIS-1 HSRS spans 0.202 µm to 2.73 µm and has a spectral resolution of 0.01 nm or better. Uncertainties are 0.3% between 0.4 and 2.365 mm and 1.3% at wavelengths outside that range

Recently, we have extended the long wavelength limit of the TSIS-1 HSRS from 2.73 µm to 200 µm with JPL SPTS solar line data through ~ 16 µm and theoretical understanding as represented in a computed solar irradiance spectrum by R. Kurucz. The extension expands the utility of this new solar irradiance reference spectrum to include Earth energy budget studies because it encompasses an integrated energy in excess of 99.99% of the total solar irradiance.

In this work, we discuss the TSIS-1 HSRS, the extension and uncertainties, and demonstrate consistency with TSIS-1 SIM and CSIM solar spectral irradiance observations and TSIS-1 Total Irradiance Monitor (TIM) total solar irradiance observations. Additionally, we compare the TSIS-1 HSRS against independent measured and modeled solar reference spectra.

How to cite: Coddington, O., Richard, E., Harber, D., Pilewskie, P., Woods, T., Chance, K., Liu, X., and Sun, K.: Extending the TSIS-1 Hybrid Solar Reference Spectrum (HSRS) to Span 0.202 to 200 um, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12777,, 2021.

Gerhard Schmidtke, Wolfgang Finsterle, Gerard Thullier, Ping Zhu, Michel Ruymbeke, Raimund Brunner, and Christoph Jacobi

A new method is presented to derive spectrally resolved global and local annual changes in the Earth Energy Imbalance (ΔEEI(λ, Δλ)) from measurements of Total and Spectral Solar Irradiance (TSI and SSI) and Total Outgoing Radiation (TOR) and the Spectral Outgoing Radiation (SOR) of the Earth. Since TSI space radiometers provide data with a long-term absolute accuracy <0.1 W m-2, the Sun should be used as a TSI referenced radiation source to obtain SSI data using the method of the Solar Auto-Calibrating XUV-IR Spectrometer (SOLACER). By repeatedly calibrating the solar and Earth observation instruments, the degradation should be compensated to accurately determine the outgoing flux Φ(λ, Δλ) entering the instrument. If the instruments on a pointing device are moved within the Angular Range of Sensitivity (ARS) in two angular dimensions through the solar disk, the instruments are also regularly calibrated with regard to their dependence of the angular sensitivity. ARS is independent of the environmental conditions. To improve the accuracy of SOR data, a normalization factor Ωa / ARS is used to extend the annual averaged outgoing flux data Φ(λ, Δλ)a to the SOR(λ, Δλ)a. The strength of the method is demonstrated by describing space-evaluated instruments to be adapted for solar and/or Earth observation from a small satellite. In the spectral range from 120 nm to 3000 nm, spectrometers and highly sensitive photometers with signal-to-noise ratios >1:107 are described to generate data records with high statistical accuracy. Given the compactness of the instruments, more than 20 different data sets should be compiled to complement, verify each other and improve accuracy.


How to cite: Schmidtke, G., Finsterle, W., Thullier, G., Zhu, P., Ruymbeke, M., Brunner, R., and Jacobi, C.: Annual Changes in the spectrally resolved global and local Earth Energy Imbalance using the Sun as a Reference Radiation Source, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7263,, 2021.

Xiao Tang, Ping Zhu, and Marta Goli

In order to upgrade the technology readiness lever of the solar and terrestrial radiation measurement from space, in this paper, we started detailed thermal analysis and modeling of the Bolometric Oscillation Sensor (BOS) using the finite element method (FEM) [1]. Four cavity shapes (cylindrical, conical, inverted conical and hemispherical) are tested to compare their thermal and optical characteristics under different radiation and thermal environment, which helps to gain a better understanding of the mechanisms of BOS. We examined the absorptivity and emissivity of each cavity shape by applying the same amount of radiation power. Especially, when the ambient temperature maintains at a stable and low value, such as 20K, it produces the most accurate reconstruction of the input power. In this presentation, we will introduce the detailed simulation result and how to apply it to correct the ambient thermal radiation on each type of detector.


[1] P. Zhu, M. Wild, M. van Ruymbeke, G. Thuillier, M. Meftah, and O. Karatekin. Interannual variation of globe net radiation flux as measured from space. J. Geophys. Res. doi:10.1002/2015JD024112, 121:6877-6891, 2016.

Acknowledgement: This work has been supported by the National Natural Science Foundation of China (NO. 41904163, 41974207), Natural Science Foundation of Hunan Province (NO. 2020JJ5483), and Research Foundation of Education Bureau of Hunan Province (NO. 18C0416). We also thank the financial support from China Scholarship Council (No. 201908430058).

How to cite: Tang, X., Zhu, P., and Goli, M.: Thermal simulation of cavity shape and its impact on solar and terrestrial radiation measurement in space, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5104,, 2021.

Wolfgang Finsterle, Margit Haberreiter, and Jean-Philippe Montillet

Solar radiometers are deployed in many locations on the ground and in space. The radiometers in space are measuring the solar energy input into the Earth system per time and unit area, also known as the Total Solar Irradiance (TSI). TSI radiometers are also used to calibrate Earth Observation instruments and to measure the Total Outgoing Radiation (TOR) at the top of the atmosphere, which is a key component in the Earth Radiation Budget (ERB). Ground-based solar radiometers measure the local irradiance levels, which are used for monitoring of atmospheric properties and solar energy applications.

Traceability of the radiation measurements to SI units is crucial in all of these applications. However, calibrating and characterising a solar radiometer is a technically challenging task. Depending on the requirements for a specific application, different calibration concepts can be employed in the calibration and characterization process.

We will present the currently available calibration concepts, their advantages and disadvantages, and put special focus on recent technical developments, such as the cryogenic standard radiometers for solar irradiance on the ground and in space.

How to cite: Finsterle, W., Haberreiter, M., and Montillet, J.-P.: How to calibrate a solar radiometer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15391,, 2021.

Margit Haberreiter, Wolfgang Finsterle, Jean-Philippe Montillet, Benjamin Walter, Bo Andersen, and Werner Schmutz

Total Solar Irradiance (TSI) is one of the Essential Climate Variables (ECV) identified by the World Meteorological Organization's Global Climate System (GCOS). The Compact Lightweight Absolute RAdiometer (CLARA) experiment onboard the Norwegian micro satellite NorSat-1 is a SI traceable radiometer and was launched July 14, 2017 with the primary science goal to measure TSI from space. We present the latest status of the data and degradation correction obtained with this SI-traceable radiometer. Besides TSI, CLARA also measures the total outgoing radiation (TOR) at the top of the Earth atmosphere on the night side of Earth, which is extremely important to understand the Earth Radiation Budget. It is to our knowledge the first time that TSI and the emitted radiation from Earth are measured simultaneously with one SI-traceable absolute radiometer. We will compare the CLARA TSI and TOR time series with other available datasets. Ultimately, we aim towards determining the Earth Energy Imbalance from space. We will discuss the achievements and limitations in direction of this goal.

How to cite: Haberreiter, M., Finsterle, W., Montillet, J.-P., Walter, B., Andersen, B., and Schmutz, W.: TSI and TOR measurements with CLARA onboard NorSat-1, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6437,, 2021.