Contributors: A. Velazquez Blazquez (Royal Meteorological Institute of Belgium (RMIB)), N. Clerbaux (Royal Meteorological Institute of Belgium (RMIB)), E. Baudrez (Royal Meteorological Institute of Belgium (RMIB)), S. Dewitte (Royal Meteorological Institute of Belgium (RMIB)), S. Nevens (Royal Meteorological Institute of Belgium (RMIB))

Issued by: RMIB/Clerbaux

Date: 04/12/2020

Ref: C3S_D312b_Lot1.1.5.1-v2.0_202003_ATBD_ECVEarthRadiationBudget_v1.1

Official reference number service contract: 2018/C3S_312b_Lot1_DWD/SC1

History of modifications

List of datasets covered by this document

Anchor
related_documents related_documents

Related documents

Acronyms

Scope of the document

This document represents the Algorithm Theoretical Basis Document (ATBD) for the generation of a Climate Data record (CDR) of Total Solar Irradiance (TSI) for the Copernicus Climate Change Service (C3S).
The aim of an ATBD is to describe the algorithms used to generate the product(s), including the scientific justification for the algorithms selected to derive the product, an outline of the proposed approach and a listing of the assumptions and limitations of the algorithm.

Executive summary

The Total Solar Irradiance (TSI) quantifies the amount of solar energy that is received by the Earth.

TSI is defined as the amount of solar power that reaches the Earth’s top of the atmosphere per unit surface perpendicular to the Sun–Earth direction at the mean Sun–Earth distance.

The TSI is a fundamental variable governing the climate system, and is recognized as ECV by the Global Climate Observing System (GCOS). Within the Copernicus Climate Change Service (C3S), a long composite Climate Data Record (CDR) is constructed from measurements of the TSI measured by 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.

This ATBD fully describes and justifies the successive steps implemented in the data processing and most of the information here contained has been reproduced from the two reference papers [D1] and [D2].

1. Introduction

The first Total Solar Irradiance (TSI) measurement from space was made with the Temperature Control Flux Monitor (TCFM) on Mariner 6 and 7 by Plamondon (1969). Continuous measurement of the TSI started with the Earth Radiation Budget (ERB) instrument on Nimbus 7 by Hickey et al. (1980). Continuous monitoring with an ageing corrected TSI instrument started with the Active Cavity Radiometer Irradiance Monitor (ACRIM) 1 instrument on the Solar Maximum Mission (SMM) by Willson et al. (1980). A summary of TSI space instruments is given in Table 1.

The instruments used for the TSI measurement are electrical substitution cavity radiometers.  Their core detector consists of a blackened cavity in which nearly all incident radiation flowing through a precision aperture is absorbed.  The thermal effect of the absorbed optical power is measured by comparison with the thermal effect of known electrical power.

A TSI radiometer ages by exposure to solar UV radiation.  For ageing correction, a backup channel is used, for which the total solar UV exposure is kept low such that the ageing of the backup channel is negligible.

Relative variations of the TSI in phase with the 11-year solar cycle of the order of 1 W/m² are now well established, as summarized by Dewitte & Nevens (2016) [D1]. Apart from these true TSI variations, differences in the absolute level above 1 W/m² are measured by different instruments indicating limitations of the absolute accuracy.

As the Sun is nearly a point source, TSI radiometers use a view-limiting mechanism to eliminate the entrance of all except direct solar radiation into the cavity. Classical radiometers place a large view-limiting aperture in front of a small precision aperture.  In this geometry, scattering and diffraction around the edges of the view-limiting aperture increase the amount of solar power flowing through the precision aperture. When this effect is underestimated it may lead to a too-high measurement of the TSI.

The Total Irradiance Monitoring (TIM) radiometers use an alternative geometry where the small precision aperture is put in front of the larger view-limiting aperture.  In this geometry, scattering and diffraction around the edges of the precision aperture decrease the amount of solar power flowing through the view limiting aperture.  When this effect is underestimated it may lead to a too-low measurement of the TSI.

Table 2 summarizes the equivalent TSI at a solar minimum measured by three independent instruments: TIM on the Solar Radiation and Climate Experiment (SORCE) in 2003, the Differential Absolute Radiometer (DIARAD) as part of the Solar Variability Irradiance Monitor (SOVIM) in 2008 and TIM on the Total Solar Irradiance Transfer Experiment (TCTE) in 2013.  We consider TIM/TCTE as more reliable than TIM/SORCE, since TIM/TCTE went through additional pre-flight characterizations as compared to TIM/SORCE.  A TSI level at a solar minimum of 1362 +/- 0.9 W/m² can be derived from the combination of DIARAD/SOVIM and TIM/TCTE [D2]. 

2. Input and auxiliary data

Summary of the instruments and data used to create the C3S daily TSI composite are shown in tables hereafter. In each table the full name, organization responsible of the data/instrument, period of time in which the TSI data is available and period of time used in the TSI composite are specified. The adjustment factors used to adjust the different absolute levels of all instruments are also provided. In addition, an illustration of the original data is shown and finally the source of the original data is provided.

3. Algorithms

3.1 Individual instrument timeseries

The difference in absolute scale between TSI instruments is larger than the intrinsic TSI variability.
Therefore a harmonization to remove the scale differences is needed. To this end, the methodology of Mekaoui & Dewitte (2008) has been followed. For a given instrument i with timeseries TSI_i (t), it is defined an absolute scale adjustment factor a_i and an adjusted timeseries a_i TSI_i(t). To determine the adjustment factor a_i, the instrument i is compared to a reference instrument ref over a chosen reference time period. Over this time period the average adjusted TSI value <a_i TSI_i(t)> is made equal to the reference value <a_ref TSI_ref(t)>, from which the adjustment for the instrument I is derived:

a_{i} = a_{ref} \frac{<TSI_{ref}(t)>}{<TSI_{i}(t)>}

The scale harmonized TSI time series is then constructed using a cascade of references as follows:

1. As initial reference absolute value , with by definition a_ref = 1, we take the average of the left and right channels of the DIARAD/SOVIM instrument (Mekaoui et al, 2010) after the revision of the so-called non equivalence between electrical and optical power as in Dewitte et al (2013b). DIARAD/SOVIM has been active during 6 months on the International Space Station (ISS) in 2008. In total six DIARAD-type radiometers have flown in space; of these, DIARAD/SOVIM is the most accurate because it has the smallest thermal nonuniformity and the best shutter design. The DIARAD-type radiometer has been kept as an independent absolute radiometer, not calibrated against other radiometers, but only compared to other radiometers for validation. The DIARAD-type radiometer has been validated by comparison with the independent LASP/TRF cryogenic radiometer, with an excellent agreement within 3 ppm concerning optical power measurement (Dewitte, 2013b). In the same measurement campaign the scattering and diffraction correction of the DIARAD-type radiometer has been validated by measuring the radiometer response to an annular illumination centered on the DIARAD view limiting aperture, with an agreement with the nominal correction within 159 ppm (Dewitte 2013b). The DIARAD/SOVIM precision apertures have been calibrated by the national metrology laboratories NPL and NIST, with an accuracy of 200 ppm.
2. Next the DIARAD/VIRGO TSI measurements (Dewitte et al. 2004) are adjusted to the DIARAD/SOVIM ones during their period of overlap. The resulting DIARAD/VIRGO adjustment factor is aDV=0.997873.
3. The PMO6/VIRGO TSI measurements (Froehlich et al. 1997) are adjusted to the DIARAD/VIRGO ones during their period of overlap. As in (Mekaoui & Dewitte, 2008) the "exposure independent ageing" from Froehlich (2003) for the backup instrument PMO6B is not applied, but the standard ageing correction of the continuously measuring PMO6A instrument by the backup PMO6B instrument is used. The resulting ageing corrected time series is called 'PMO6B/VIRGO'. The PMO6B/VIRGO adjustment factor is aPV=0.998241.
4. The ACRIM2 measurements (Willson 1994) are adjusted to the DIARAD/VIRGO ones during their period of overlap excluding the first year of DIARAD/VIRGO operation. The ACRIM2 adjustment factor is aA2=0.999220.
5. The ACRIM3 (Willson 2014) are adjusted to the DIARAD/VIRGO ones during their period of overlap excluding the first two years of ACRIM3 operation. The ACRIM3 adjustment factor is aA3=1.001572.
6. The TIM/SORCE measurements (Kopp et al. 2003) are then adjusted to the DIARAD/VIRGO ones during their period of overlap. The TIM/SORCE adjustment factor is aTS=1.001850.
7. The Sova-Picard measurements (Dewitte et al. 2012) are adjusted to the DIARAD/VIRGO ones during their period of overlap. The adjustment factor is aSP=1.001152.
8. The PREMOS/Picard measurements (Schmutz et al. 2012) are adjusted to the DIARAD/VIRGO ones during their period of overlap. The Premos/Picard adjustment factor is aPRE=1.001719.
9. The TIM/TCTE measurements (TCTE 2014) are adjusted to the DIARAD/VIRGO ones during their period of overlap. The adjustment factor is a_TT=1.001267.
10. The ERBS measurements (ERBE 1986) are adjusted to the ACRIM 2 ones during their period of overlap. As the ERBS sampling period is 14 days, and as the ERBS measurements are relatively noisy, the "denoised" ERBS version from Mekaoui and Dewitte (2008) is used. The ERBS adjustment factor is aDV=0.998496.
11. The ACRIM1 measurements (Willson et al. 1981) are adjusted to the ERBS ones during their period of overlap. The ACRIM1 adjustment factor is aA1=0.996863.
12. Finally the ERB/Nimbus7 measurements (Hickey et al 1980) are adjusted to the ACRIM1 ones during their period of overlap. The ERB/Nimbus7 adjustment factor is aN7=0.993833.

Figure 1 shows the resulting scale harmonized TSI measurements from the individual TSI instruments. For clarity we use a 121 day running mean to remove the short term solar noise, and to highlight the instrumental differences.

Figure 1. Time series of individual TSI measurements after scale harmonization. A 121-day running mean is used to remove the short-term solar noise. ERB/Nimbus 7 (1981-1990). ACRIM1 (1980–1989), ACRIM2 (1991–2001), ACRIM3 (2002–2013). DIARAD/VIRGO (1997–2020), Sova-Picard (2010–2014)., PMO6/VIRGO (1997–2018), Premos (2010–2014). TIM/SORCE (2003–2020), TIM/TCTE (2015–2020), TIM/TSIS(2018-2020).

3.2 Construction of a composite time series

3.2.1 Apparent Drift of the TIM/SORCE Instrument

Close examination of Figure 1 shows that the TIM/SORCE TSI values start lower during solar cycle 24 and end higher during solar cycle 25 than any of the independent overlapping instruments (DIARAD/VIRGO, PMO6B/VIRGO, and ACRIM3). This is highlighted in Figure 2, where we plot the (adjusted) TIM/SORCE timeseries compared to the daily composite constructed using the C3S methodology (described in this ATBD document) but discarding TIM/SORCE as input instrument. There is a good agreement at beginning of the SORCE mission (when the adjustment factor is evaluated) but later there is a progressive divergence of the two timeseries.

Figure 2. Timeseries of adjusted TIM/SORCE TSI (daily in green and 121-days running mean in blue) compared to the TSI composite obtained discarding TIM/SORCE instrument (black and red curves).

Figure 3 shows the difference between TIM/SORCE and this independent composite. A relatively linear temporal drift is observed over the 1/1/2004 to 31/12/2013 time period, i.e. over 10 years. The green curve shows the linear drift of 0.03 W/m²/year between 2004 and 2014. To correct this temporal drift, it is proposed to reduce the TIM/SORCE TSI by -0.03W/m²/year after 2004. For 2014 onward, the drift is less obvious to model and it is proposed to keep the correction at a constant value of -0.3 W/m².

Figure 3. Difference between (adjusted) TIM/SORCE and the TSI composite obtained without considering TIM/SORCE. The black curve shows the daily difference and the red the 121-days running mean difference. The green line is the proposed modelling of the drift.

As an independent evaluation of this correction, a comparison with the SATIRE-S reconstruction is provided on Figure 4 and Figure 5. Figure 4 shows the original TIM/SORCE and SATIRE-S timeseries.

Figure 4. TIM/SORCE (original, not corrected not adjusted) and SATIRE-S timeseries. For each one, the daily values and the 121-days running mean are shown.

Figure 5 shows the difference without and with the -0.03W/m²/year aging correction. After correction (green and blue curves), the stability remains within 0.15 W/m² (see dashed lines at -0.03 W/m² and -0.18 W/m²).

Figure 5. Difference between TIM/SORCE and SATIRE-S timeseries (black: daily value, red: 121-days running mean). The green (daily) and blue (121-days running mean) curves show the difference after the aging correction of the TIM/SORCE TSI. The dashed lines illustrate the stability of the aging-corrected TIM/SORCE record.

3.2.2 Discarding of Early Drift and Late Shift Periods

Instrumental effects in individual TSI instruments can mask the true solar variation. Besides the apparent TIM/SORCE drift mentioned above, we identify the following instrumental effects by intercomparison of individual TSI instrument measurements as shown in Figure 1:

1. During the first 2 years of ACRIM3 operation, the TSI values are higher than those of the older DIARAD/VIRGO and PMO6/VIRGO TSI instruments, while ACRIM3 agrees well with the other instruments later on. This is illustrated in Figure 6, which shows the VIRGO measurements and the ACRIM3 measurements during the first years of ACRIM3 operation. In general, it is more likely that an instrument drifts in the beginning of its lifetime than later on. The launch and first switch-on in space is a discontinuity to which the instrument has to adapt, and which may affect the instrument's reading. Thus, an early drift of ACRIM3 is possible. In contrast, it is very unlikely that both of the seasoned DIARAD/VIRGO and PMO6/VIRGO instruments start drifting several years after their launch at the same time and with the same magnitude coinciding with the ACRIM3 launch. It thus seems likely that ACRIM3 had an early instrumental drift during its first 2 years of operation, and we discard ACRIM3 data from this period for further use.
2. During the first year of VIRGO operation, the TSI values of DIARAD/VIRGO and of PMO6/VIRGO are increasing, while the TSI values measured by the older ACRIM2 and ERBS instruments remain flat. This is illustrated in Figure 7, which shows the ERBS and ACRIM2 measurements together with the VIRGO measurements during the first years of VIRGO operation. Following a similar reasoning as above, it is more likely that the VIRGO radiometers have an early drift while they are fresh in space than it would be for the seasoned ACRIM2 and ERBS radiometers to start drifting at the same time and with the same magnitude. The early increase of the VIRGO radiometers is also discussed in Froehlich (2003). It thus seems likely that the VIRGO radiometers have an early instrumental drift during their first year of operation, and we discard VIRGO data from this period for further use. The removal of the early data does not influence the absolute value, since we use DIARAD/VIRGO only as a transfer radiometer calibrated by DIARAD/SOVIM, not as an absolute radiometer.
3. At the end of its lifetime, during the so-called "ACRIM gap" period in between ACRIM1 and ACRIM2, the ERB/Nimbus 7 instrument had abrupt shifts (Lee et al. 1995; Chapman et al. 1996) when comparing it to commonly used TSI regression models that reproduce the TSI variation from sunspot and facula indices (see D4). Physically it seems hard to understand how the true TSI could vary in a discontinuous way, while instrumental discontinuities can never be excluded. Also, during the ACRIM gap, the ERBE TSI was compatible with commonly used TSI regression models (Lee et al. 1995), while the ERB/Nimbus 7 TSI was not. This is illustrated in Figure 8, which shows the ERB, ACRIM1, ERBS, and ACRIM2 TSI together with a TSI proxy model—which is described in D4—for the period 1988–1994. Thus, it seems likely that the ERB/Nimbus 7 suffered from instrumental degradation during the ACRIM gap, and therefore we discard the ERB/Nimbus 7 data after 1990.
4. The ACRIM1 instrument was launched on the SMM spacecraft in 1980 February. From 1980 November to 1984 April the SMM attitude control was degraded, leading to the so-called "ACRIM1 spin period" (Willson 1994). In the version 2 of the dataset ACRIM1 data is used even during the spin period as no other reliable dataset is available for the year 1980. Data used is comparable to SATIRE-S dataset.
5. The ERB/Nimbus 7 did not have the capability for independent aging monitoring and correction. We only consider it as reliable when it can be compared with an independent trusted instrument, namely, ACRIM1. For v2.0 of the C3S composite data from 1981 onwards is used.
6. During the solar minimum from 1984 to 1987, the ERBS instrument was fresh in space and could be subject to early drifts. By precaution we discard the ERBS data for this period, and we only rely on the older ERB and ACRIM1 instruments.

Figure 6. 121-day running mean TSI values of DIARAD/VIRGO, PMO6B/VIRGO, and ACRIM3 for the period 2000–2006. Figure reproduced from D1.

Figure 7. 121-day running mean TSI values of ERBS, ACRIM2, DIARAD/VIRGO, and PMO6B/VIRGO for the period 1995–2000 . Figure reproduced from D1.

Figure 8. 121-day running mean TSI values of ERB, ACRIM1, ERBS, and ACRIM2 measurements and Mount Wilson magnetogram based regression model for the period 1995–2000. Figure reproduced from D1

Figure 9 shows the retained "quality-controlled" TSI instrument time series. These quality-controlled time series are consistent within +/−0.25 W m−2 over the entire period from 1979 to 2020, while in the original time series from Figure 1 deviations of up to 0.7 W m−2 exist.

Figure 9. Time series of individual TSI measurements after drift correction TIM/SORCE and removal of early drift and late shift period for ERB, and removal of early drift periods for ERBS, DIARAD/VIRGO, PMO06-B/VIRGO, and ACRIM3. ERB/Nimbus 7 (1981-1990). ACRIM1 (1980–1989), ACRIM2 (1991–2001), ACRIM3 (2002–2013). DIARAD/VIRGO (1997–2020), Sova-Picard (2010–2014)., PMO6/VIRGO (1997–2018), Premos (2010–2014). TIM/SORCE (2003–2020), TIM/TCTE (2015–2020), TIM/TSIS(2018-2020).

3.2.3 Gap filling

For some of the TSI instruments, the timeseries presents frequent missing daily values over some periods. It is the case of the ERB measurements at the beginning of the composite and also of the TSIS instrument at the end of the composite. In version 2.x of the C3S daily TSI composite, a gap filling mechanism is implemented as preprocessing of the original timeseries. Gaps are filled provided they extend over less than 50 days.
The gap filling exploits the SATIRE-S reconstruction which is tuned to the observations made just before and just after the gap. In practice, the ratio between the observed TSI and the SATIRE-S reconstruction is evaluated for the last day before the data gap and for the first day following the gap. This ratio is then temporally interpolated for any day within the data gap and the TSI for this day is obtained from the SATIRE-S reconstruction corrected with this interpolated ratio.

3.2.4 Composite

From the individual time series of Figure 9, on a daily basis the composite TSI value is calculated as the mean of all available TSI values. The resulting composite is then scaled using an overall factor ( 

a = 0.5 \ast \left(1+ \frac{1}{a_{TT}} \right) = 0.9993367

) to set the minimum level of the TSI composite to the mean value of DIARAD and TIM TCTE at their minimum [see Table 2 and D2].

Figure 10 shows the resulting TSI measurements; the red curve shows the daily mean values, while the green curve shows the 121-day running mean values.

Figure 10. Composite TSI values. Red curve: daily mean TSI measurements. Green curve: 121-day running mean TSI measurements. Blue curve: 121-day running mean TSI Mount Wilson regression model.

The downward spikes in the daily mean values are due to the passage of dark sunspots, temporarily decreasing the TSI values. This is the sunspot deficit effect.

The general increase of the TSI with solar activity highlighted by the 121-day running mean values is due to the increase of long-living bright faculae during high solar activity. This is the facular excess effect.

4. Output data

The output format is fully described in the Product User Guide and Specifications document [D3] for this data record. Here, only the main characteristics are provided, as well as an illustration for each field.

4.1 General characteristics of the CDR

4.2 Total Solar Irradiance

The Total Solar Irradiance is the spectrally integrated total amount of radiant energy coming from the Sun per square meter of surface, perpendicular to the sunlight, at 1 astronomical unit.

An illustration of incoming total solar irradiance is provided in Figure 11.

Figure 11. Total Solar Irradiance composite from RMIB

References

Chapman, G. A., Cookson, A. M., and Dobias, J. J. (1996). Variations in total solar irradiance during solar cycle 22, J. Geophys. Res., 101(A6), 13541– 13548, doi:10.1029/96JA00683.

Crommelynck, D., Domingo, V., Fichot, A., & Lee, R. (1994). Total Solar Irradiance Observations from the EURECA and ATLAS Experiments. International Astronomical Union Colloquium, 143, 63-69. doi:10.1017/S0252921100024544

Crommelynck, D.; Brusa, R.; Domingo, V (1987). Results of the solar constant experiment onboard Spacelab-1. Solar Phys, 107, 1–9.

Dewitte S. (2013b). The Contribution of the DIARAD Type Radiometer to the Revision of the Solar Constant Technical Note.
Available at ftp://gerb.oma.be/steven/RMIB_TSI_composite/ diaradnewsolarconstant.pdf

Dewitte, S., Crommelynck, D., and Joukoff, A. (2004). Total solar irradiance observations from DIARAD/VIRGO, J. Geophys. Res., 109, A02102, doi:10.1029/2002JA009694.

Dewitte, S., Janssen, E. and Mekaoui, S., (2013a). May. Science results from the Sova-Picard total solar irradiance instrument. In AIP Conference Proceedings (Vol. 1531, No. 1, pp. 688-691). AIP. doi:10.1063/1.4804863
ERBE Science Team (1986). First data from the Earth Radiation Budget Experiment.BAMS, 67, 818--824.

Fang, W.; Wang, H.; Li, H.; Wang, Y. Total Solar Irradiance Monitor for Chinese FY-3A and FY-3B Satellites: Instrument Design (2014). Solar Phys, 289, 4711–4726.

Froehlich, C. (2003). Long-Term Behaviour of Space Radiometers, Metrologia,40, 60-65.

Froehlich, C., Crommelynck, D.A., Wehrli, C. et al. (1997). In-Flight Performance of the Virgo Solar Irradiance Instruments on Soho. Sol Phys 175, 267–286. doi:10.1023/A:1004929108864

Hickey, J. R. et al. (1976). Extra-Terrestrial Solar Irradiance Measurements from the Nimbus 6 Satellite, Proc. Joint Conference on Sharing the Sun, Winnipeg, Manitoba, Canada.

Hickey, J.R., L.L. Stowe, H. Jacobowitz, P. Pellegrino, R.H. Machhoff, F. House, T.H. Vonder Haar (1980). Initial solar irradiance determinations from nimbus 7 cavity radiometer measurements, Science, 208, 281--283.

Kopp, G. (2020), TSIS TIM Level 3 Total Solar Irradiance 24-hour Means, version 03, Accessed 01.10.2020 at doi:10.5067/TSIS/TIM/DATA306

Kopp, G. Solar Variability Magnitudes and Timescales (2016). J. Space Weather Space Clim, 6, A30

Kopp, G., Lawrence, G. & Rottman, G. (2005). The Total Irradiance Monitor (TIM): Science Results. Sol Phys 230, 129–139. doi:10.1007/s11207-005-7433-9

Lee, R. B., Gibson, M. A., Wilson, R. S., and Thomas, S. (1995). Long‐term total solar irradiance variability during sunspot cycle 22, J. Geophys. Res., 100(A2), 1667– 1675, doi:10.1029/94JA02897

Mekaoui, S., Dewitte, S. (2008). Total Solar Irradiance Measurement and Modelling during Cycle 23. Sol Phys 247, 203–216. doi:10.1007/s11207-007-9070-y

Mekaoui, S., Dewitte, S., Conscience, C. and Chevalier, A. (2010). Total solar irradiance absolute level from DIARAD/SOVIM on the International Space Station. Advances in Space Research, 45(11), pp.1393-1406.
Mount Wilson Observatory (2013). The 150-foot Solar Tower Current Selected Data (Mt. Wilson, CA: Mount Wilson Institute), http://obs.astro.ucla.edu/150_data.html+

Greenbelt, MD, USA: NASA Goddard Earth Science Data and Information Services Center (GES DISC),

Plamondon, (1969): TCFM solar observations on Mariner 6, JPL Space Program Summary, 3, 162.

Romero, J., Wehrli, C. & Fröhlich, C. (1994). Solar total irradiance variability from SOVA 2 on board EURECA. Sol Phys 152, 23–29 doi:10.1007/BF01473178

Schmutz W., Fehlmann A., Finsterle W., Kopp G., Thuillier G. (2012). Total solar irradiance measurements with PREMOS/Picard, AIP Conf. Proc, 1531, 624. doi: 10.1063/1.4804847

Sklyarov, Y.; Brichkov, Y.; Vorobev, V.; Kotuma, A. (1996). The satellite borne instrument Solar-Constant Gauge. Astron. Lett., 22, 318–320

TCTE 2014, Total Solar Irradiance Calibration Transfer Experiment (Boulder, CO: Univ. of Colorado), http://lasp.colorado.edu/home/tcte/data+

Wang, H.; Wang, Y.; Ye, X.; Yang, D.; Wang, K.; Li, H.; Fang, W. Instrument Description: The Total Solar Irradiance Monitor on the FY-3C Satellite, an Instrument with a Pointing System (2017) . Solar Phys, 289, 8

Willson, R. (1994). Irradiance Observations of SMM, Spacelab 1, UARS, and ATLAS Experiments. International Astronomical Union Colloquium, 143, 54-62. doi:10.1017/S0252921100024532

Willson, R.; Mordvinov, A. Secular total solar irradiance trend during solar cycles 21–23 (2003). GRL, 30, 1199.

Willson, R.C. (2014). ACRIM3 and the Total Solar Irradiance database. Astrophys Space Sci 352, 341–352. doi:10.1007/s10509-014-1961-4

Willson, R.C., S. Gulkis, M. Janssen, H.S. Hudson, G.A. Chapman, (1980): Observations of Solar Irradiance Variability, Science, 211, 700 - 702. doi: 10.1126/science.211.4483.700

Related articles