SPECTRAL from Helioclim-3

Last update: Oct. 2018

   Introduction - Inputs - Outputs - Automatic access - Bibliography



   This service provides spectral radiation values computed from the satellite-derived solar radiation database HelioClim-3 version 5 over a horizontal plane. The geographical coverage corresponds to the Meteosat satellite field of view, i.e. covers Europe, Africa, Atlantic Ocean, Middle East. Spatial resolution is 3 km at Nadir and is increasing as soon as we get away from this point (see illustration on the right hand side). Temporal coverage of data is 2004-02-01 up to current day-2, and soon in real time. Time reference is UT.

So far, two services are available:

Ultra-Violet from HC3

The service provides time series of UV-A (315–400 nm) and UV-B (280–315 nm), and UV total data.
Data are irradiances in W/m².

Bibliography: the algorithm of conversion from total radiation (i.e. spectrally integrated) into UV-A, -B or total is described in Wald 2012 (see list of publications below). Aculinin et al. 2016 provide an interesting comparison of several methods.

Photosynthetically Active Radiation from HC3

The service provides time series of PAR (400-700 nm) in all weather conditions, in cloud-free conditions, and at the top of the atmosphere. The method used here is Udo et Aro (1999). For more details about the evaluation of the performance of several methods to derive PAR from satellite imagery over 3 stations in Southern UK, please take a look to this poster and read our page dedicated to research. Provided datasets are photosynthetic photon flux density, abbreviated in PPFD and expressed in µmol.m-2.s-1. It is defined as the number of the incident photons per unit time per unit surface. This unit is linked to irradiance by the widely used approximation 1 W.m−2 ≈ 4.57 µmol.m-2.s-1 (McCree, 1972).


  • Spectral band: Select the spectral range: "Ultraviolet (UV)" or "Photosynthetically Active Radiation (PAR)".
  • Latitude and longitude: enter the values in decimal degrees (we advise 3 or 4 digits after comma), or directly click on the map to select your point, or you can also use the "Search Address" tool on the top of the map.
  • Altitude: enter the altitude, or let us use our default high resolution elevation database SRTM (spatial resolution 90 m, uncertainty 10 m) by letting the default "Automatic" value.
  • Start date and End date: format yyyy-mm-dd.
    NB: Please pay attention to ask for complete months when asking for monthly values. If incomplete, the given monthly value results from an interpolation based on the selected days.
  • Time step: "15 min", "30 min", "hour", "day".
  • Compute relief shadows: take into account (or not) the shadowing effect due to the far horizon.
  • Output format: CSV


UV from HC3

  1. Date: format DD-MM-YYYY
  2. Time: format hh:mm
  3. UVA: Irradiation in UV-A (315-400 nm) over the period on horizontal plane (-999 if not data)
  4. UVB: Irradiation in UV-B (280-315 nm) over the period on horizontal plane (-999 if no data)
  5. UV: Irradiation in UV (280-400 nm) over the period on horizontal plane (-999 if no data)

PAR from HC3

  1. Date: format DD-MM-YYYY
  2. Time: format hh:mm
  3. PAR (µmol/m2/s): PAR (400-700 nm) over the period on horizontal plane (-999 if no data)
  4. PAR clear-sky (µmol/m2/s): PAR (400-700 nm) over the period on horizontal plane in cloud-free conditions (-999 if no data)
  5. PAR TOA (µmol/m2/s): PAR (400-700 nm) over the period on horizontal plane at the top of the atmosphere (-999 if no data)
  6. Code: 0: no data, 1: sun below horizon, 2: satellite assessment, 5: interpolation in time, 6: forecast

Top of page

Bibliography Spectral

(In alphabetic order and and reverse chronological order)

Aculinin et al. 2016 Aculinin A., C. Brogniez, M. Bengulescu, D. Gillotay, et al. 2016. "Assessment of Several Empirical Relationships for Deriving Daily Means of UV-A Irradiance from Meteosat-Based Estimates of the Total Irradiance" Remote Sensing, MDPI, 2016, 8 (7), pp.537. UV-A from broadband


Boniol et al. 2006 Boniol, M., Cattaruzza, M. S., Wald, L., Chignol, M. C., Richard, M. A., Leccia, M. T., Truchetet, F., Renoirte, C., Vereecken, P., Autier, P., and Doré, J.-F., 2006. "Individual sun exposure can be assessed using meteorological satellite measurements". Epidemiology, 17(6), S245. UV and health


Bosch et al. 2009 Bosch, J.L., G. López, F.J. Batlles (2009). Global and direct photosynthetically active radiation parameterizations for clear-sky conditions. Agricultural and Forest Meteorology. 149. 146-158. 10.1016/j.agrformet.2008.07.011. PAR

Content: coefficient to derive PAR ground albedo from broadband ground albedo.

Boyle et al. 2006 Boyle, P., Boniol, M., Doré, J.-F., Chignol, M.-C., and Wald, L., UV-France, 2006. "Measurement of individual and population exposure to ultraviolet radiation based on data from meteorological satellites", Epidemiology. 17(6), S306. UV and health


Harmel and Chami 2016 Harmel, T. and M. Chami (2016). Estimation of daily photosynthetically active radiation (PAR) in presence of low to high aerosol loads: Application to OLCI-like satellite data. Optics Express. 24. A1390-A1407. 10.1364/OE.24.0A1390. PAR

Content: data BOUSSOLE

Jacovides et al. 2004 Jacovides, C. P., Timvios, F. S., Papaioannou, G., Asimakopoulos, D. N., and Theofilou, C. M.: Ratio of PAR to broadband solar radiation measured in Cyprus, Agr. Forest. Meteorol., 121, 135– 140, 2004. PAR from HC3

Content: Coeff to derive PAR from GHI optimized for Cyprus.

Kato et al. 1999 Kato S., T. Ackerman, J.  Mather, E. Clothiaux, 1999. "The k-distribution method and correlated-k approximation  for  shortwave  radiative  transfer  model" Journal of Quantitative Spectroscopy and Radiative Transfer 62, 109-121. DOI:10.1016/S0022-4073(98)00075-2. Kato


Kravietz et al. 2017 Kravietz A., S. Ka, L. Wald, A. Dugravot, A. Singh-Manoux, F. Moisan, A. Elbaz, 2017. "Association of UV radiation with Parkinson disease incidence: a nationwide French ecologic study" Environmental Research, 154, 50 - 56, doi: 10.1016/j.envres.2016.12.008 UV and Parkinson desease


Lefèvre et al. 2013 Lefèvre M., A. Oumbe, P. Blanc, B. Espinar, B. Gschwind, Z. Qu, L. Wald, M. Schroedter-Homscheidt, C. Hoyer-Klick, A. Arola, A. Benedetti, J. W. Kaiser, and J.-J.  Morcrette, 2013. "McClear: a new model estimating downwelling solar radiation at ground level in clear-sky conditions", Atmos. Meas. Tech., 6, 2403-2418, doi:10.5194/amt-6-2403-2013. McClear

Content: in addition to the description of CAMS McClear, this article provides a very restrictive algorithm to select clear sky instants. It consists of two successive filters. The first one is a constraint on the amount of diffuse irradiance with respect to the global irradiance since the direct irradiance is usually prominent in the case of clear sky. The second filter analyses the temporal variability of the global irradiance. If there is no cloud, the sky should be clear and steady for a long period.

Lisicki et al. 2017 Marco Lisicki, Kevin D'Ostilio, Michel Erpicum, Jean Schoenen, Delphine Magis, 2017. "Sunlight irradiance and habituation of visual evoked potentials in migraine: The environment makes its mark", Cephalagia, Vol 38, Issue 7, 2018, https://doi.org/10.1177/0333102417730128 UV and Health

Content: UV and Migraines

McCree 1972 McCree, K. J.. "Test of current definitions of photosynthetically active radiation against leaf photosynthesis data", Agric. Meteorol., 10, 443–453, 1972 conversion factor from µmol/m2/s into W/m2


Mesrine et al. 2017 Mesrine S., M. Kvaskoff, T. Bah, L. Wald, F. Clavel-Chapelon, et al., 2017. "Ambient Ultraviolet Radiation, and Thyroid Cancer Risk: A French Prospective Study". Epidemiology, 2017, 28, pp.694-702. UV and Health


Opálková et al. 2018 Opálková, M., Navrátil, M., Špunda, V., Blanc, P., and Wald, L.. "A database of 10 min average measurements of solar radiation and meteorological variables in Ostrava, Czech Republic", Earth Syst. Sci. Data, 10, 837-846, https://doi.org/10.5194/essd-10-837-2018, 2018. GRD measurements, UV, PAR, broadband, Czech Republic

Content: Article which proposes an alternative of quality check for spectral radiation values.
https://doi.org/10.1594/PANGAEA.879722 proposes for free in-situ measurements for 3 sites (2 very close) close to Ostrava, in Czech Republic:

  • BGOU S1: lat=49.82754°, 18.32618°, 10 min data in UTC, end of interval, averages. Data from 2014-07-01-00-00 to 2016-12-31-22-50.
  • BGOU S2: idem except data start on 2014-07-02-08-00
  • NB: PHI (proche BGOU) provides meteo variables and air-pollutant information at a 1h time step.
  • CHMI S3: lat=49.82521°, 18.15932°, 10 min data in UTC, end of interval, averages. Data from 2014-07-07-13-00 to 2016-12-31-22-50.

Spectral bands: UVB: 280-315 nm, UVA 315-400 nm, PAR 400-700 nm, 510-700 nm, 600-700 nm, 610-680 nm, 690-780 nm, broadband 400-1100 nm.

Interesting citations in this article:

  • "Moreover, diffuse radiation is know for having a different blue/red ratio compared to direct radiation (Navratil et al. 2007)."
  • "We have adapted the approach of Korany et al. (2016) which applies to measurements of global and diffuse total irradiances."
  • "Some values are greater than the corresponding irradiance at TOA. These values were usually connectly with partly cloudy weather, when multiple scattering on the cloud edges could increase incident solar irradiation (Mims and Frederick, 1994)."
Orton et al. 2011 Orton S.-M., L. Wald, C. B. Confavreux, S. Vukusic, J. P. Krohn, et al. 2011. "Association of UV radiation with multiple sclerosis prevalence and sex ratio in France", Neurology, 2011, 76 (5), pp.425-431. UV and health


Porcheret et al. 2018 Porcheret K., L. Wald, L. Fritschi, M. Gerkema, M. Gordijn, et al. 2016. "Chronotype and environmental light exposure in a student population", Chronobiology International, doi: 10.1080/07420528.2018.1482556, 2018 UV and Health


Savoye et al. 2018 Savoye I., C. Olsen, D. Whiteman, A. Bijon, L. Wald, et al., 2018. "Patterns of ultraviolet radiation exposure and skin cancer risk: the E3N-SunExp study". Journal of Epidemiology, 2018, 28(1), pp.27-33. UV and Health


Savoye et al. 2016 Savoye I., C. Olsen, L. Wald, F. Clavel-Chapelon, M.-C. Boutron-Ruault, et al., 2016. "Profils d'exposition solaire et risque de cancer cutané : étude cas-témoin nichée dans E3 N". Epidemiology and Public Health / Revue d'Epidémiologie et de Santé Publique, 2016, 64, pp.S224 UV and health


Szeicz 1974 Szeicz G., 1974. "Solar radiation for plant growth", J. Appl Ecol., Vol. 11, No. 2 (Aug., 1974), pp. 617-636. DOI: 10.2307/2402214 PAR from GHI, UK
Content: Coeff to derive PAR from GHI optimized for England.


Udo et Aro 1999 Udo, S. O. and Aro, T. O., 1999. "Global PAR related to global solar radiation for central Nigeria", Agr. Forest. Meteorol, 97, 21–31, 1999. https://doi.org/10.1016/S0168-1923(99)00055-6 PAR from broadband

Content: Coeff to derive PAR from GHI optimized for Nigeria.

Wald 2018 Lucien Wald, 2018. "A simple algorithm for the computation of the spectral distribution of the solar irradiance at surface"  [Research Report] MINES ParisTech. 2018. Spectral from broadband


Wald 2012 Wald L., 2012. "Elements on the Computation of UV Maps in the Eurosun Database" Internal Report. 2012. UV from broadband


Wandji Nyamsi et al. 2019 Wandji Nyamsi W., P. Blanc, J.A. Augustine, A. Arola, and L. Wald, 2019. "A new clear-sky method for assessing photosynthetically active radiation at the surface level", Atmosphere 2019, 10, 219; doi:10.3390/atmos10040219. PAR from Kato


Wandji Nyamsi et al. 2017 Wandji Nyamsi W., M. R. A. Pitkänen, Y. Aoun, P. Blanc, A. Heikkilä, K. Lakkala, G. Bernhard, T. Koskela, A. V. Lindfors, A. Arola, et al., 2017. "A new method for estimating UV fluxes at ground level in cloud-free conditions" Atmospheric Measurement Techniques, European Geosciences Union, 2017, 10 (12), pp.4965-4978. DOI:10.5194/amt-10-4965- 2017. UV from Kato


Wandji Nyamsi 2015

Thèse de William Wandji Nyamsi W., 2015. "Vers une méthode automatique d'estimation de la distribution spectrale du rayonnement solaire. Cas du ciel clair. : Applications à la lumière du jour, photosynthèse et ultraviolet". Soutenue le 6 novembre 2015. MINES ParisTech, spécialité « énergétique et procédés », 124 p.

PAR et UV from Kato


Wandji Nyamsi et al. 2015

Wandji Nyamsi W., B. Espinar, P. Blanc, and L. Wald, 2015. "Estimating the photosynthetically active radiation under clear skies by means of a new approach" Advances in Science and Research, Copernicus Publications, 12, pp.5–10. DOI: 10.5194/asr-12-5-2015

PAR from Kato

Content: the Kato bands do not exactly fit the PAR spectral ranges and a spectral resampling is necessary. The authors have developed a resampling method which determine several 1-nm spectral bands whose atmospheric transmissivities are correlated to those of the Kato bands and then use these transmissivities in a linear interpolation process to compute the PAR irradiance. The technique has been numerically validated. The authors conclude that the technique estimates direct and global with very high accuracy. 

Wandji Nyamsi et al. 2014 Wandji Nyamsi W., B. Espinar, P. Blanc, and L. Wald, 2014. "How close to detailed spectral calculations is the k-distribution method and correlated-k approximation of Kato et al. (1999) in each spectral interval?" Meteorologische Zeitschrift, Borntraeger Science Publishers, 2014, 23, pp.547-556. DOI: 10.1127/metz/2014/0607. Kato

Content: authors compared atmospheric transmissivities obtained by the Kato et al. approach against those obtained by spectrally resolved computations using two Radiative Transfer Models (RTMs) in each of the 32 Kato Bands. These calculations were performed for a set of 200 000 realistic atmospheres and clouds. These authors found that the Kato et al. approach offers very accurate estimates of irradiances in all 12 Kato bands covering PAR-range.

Yu et al. 2015 Xiaolei Y., Z. Wu, W. Jiang, and X. Guo, 2015. "Predicting daily photosynthetically active radiation from global solar radiation in the Contiguous United States", Energy Conversion and Management, Vol. 89, pp. 71-82. DOI: 10.1016/j.enconman.2014.09.038 PAR from GHI
Content: Table 1 gives a very interesting summary of previous studies for estimating PAR from GHI (Rs in the text). This is where I found Szeicz


Top of page