Photosynthetically Active radiation (PAR)

Last update: May 2019

    Presentation - Characteristics of the service - Steps of developments - Bibliography

Presentation of this activity


Evaluate the performance of 13 methods to assess PAR from satellite imagery at several ground stations. This axis of research and development was defined to fulfill the second most frequent demand from users to receive spectrally-resolved datasets.

The objective is to define the most adequate sets of services for SoDa based on the comparison of several methods developed by OIE and by other research laboratories.

The Illustration on the right hand side depicts the locations of the processed and to-be-processed ground measurements =>


List of processed stations in alphabetic order (to be processed in gray background, and in cloud-free conditions in orange background)

Station Code Country Latitude Longitude Altitude (m) Period Provider - Network Type of climate
Abbotts Hall ABT UK 60.133 -1.183 84 2004-2007 CBESS Oceanic
Aberystwyth University ABU Estonia 58.254 26.462 70 2004-2014 CBESS Oceanic
Bily Kriz Forest - CO2 enrichment experiment BKF_control Czech Rep. 49.502 18.539   2008-05-01 to 2011-11-02 GCAS Continental
Bily Kriz Forest - Norway spruce forest before thinning BKF_DF Czech Rep. 49.502 18.537   2004-04-29 to 2007-11-01 GCAS Continental
Bondville BON USA 40.05 -88.37 230 2010-01-01 to 2016-12-31 SURFRAD Continental
Boulder BOU USA 40.12 -105.24 1689 2010-01-04 to 2016-12-31 SURFRAD Continental
Cartmel Sands CAS Germany 52.210 14.122 125 2004-2007 CBESS Oceanic
Desert Rock DSR USA 36.62 -116.02 1007 2010-01-12 to 2016-12-29 SURFRAD Continental
Fort Peck FPK USA 48.31 -105.10 634 2010-02-10 to 2016-12-21 SURFRAD Continental
Goodwin Creek GWC USA 34.25 -89.87 98 2010-01-01 to 2016-12-30 SURFRAD Continental
Pennsylvania PSV USA 40.72 -77.93 376 2010-01-09 to 2016-11-23 SURFRAD Continental
Peronne Saint-Quentin PSQ Netherlands 51.971 4.927 0 2005-2014 INRA - ICOS Continental
Plataforma Solar de Alméria PSA UK 50.217 -5.317 88 2004-2007 CIEMAT Continental - Mediterranean
Siouxfalls SXF USA 43.73 -96.62 473 2010-01-01 to 2016-12-31 SURFRAD Continental
Třeboň Wetland TRE Czech Rep. 49.025 14.770 425 2006-04-29 to 2017-12-31 GCAS Continental

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13 methods to assess PAR from satellite imagery

  1. Udo et Aro (1999) applied onto broadband GHI from HelioClim-3
  2. Szeicz (1974) on HC3
  3. Jacovides (2004) on HC3
  4. Wald on HC3 (Internal Report 2018)
  5. Weighted_Kato on HC3 (Wandji Nyamsi et al. 2014, 2015, and 2019)
  6. Discretized_Kato on HC3 (Wandji Nyamsi et al. 2014, 2015, and 2019)
  7. Udo et Aro applied onto GHI from CAMS Radiation Service
  8. Szeicz on CAMS-Rad
  9. Jacovides on CAMS-Rad
  10. Wald on CAMS-Rad
  11. Weighted_Kato on CAMS-Rad
  12. Discretized_Kato on CAMS-Rad
  13. DWD SARAH-3

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Publications of this work - project applications

EMS Conference 2018

Presentation of the preliminary results for the evaluation of the performance of 5 methods to assess PAR from satellite imagery at the following locations:

  • Aberystwyth University (30 min means, middle of interval UTC)
  • Abbotts Hall                  (30 min means, middle of interval UTC)
  • Cartmels Sands            (30 min means, middle of interval UTC)
  • and 4 short-term and limited quality measurements (Apr.-Aug. 2018, 15 min instantaneous)

(Collaboration with the University of East Anglia, FMI, Transvalor and MINES ParisTech)

Click to magnify=>

Peer-reviewed article ASR 2019

From the poster, an article has been proposed in January 2019. Status: under review.

EMS conference 2019: Copenhagen

An abstract has been submitted to this conference as an extension of the work proposed in the poster the year before. The 13 satellite methods will be confronted to at least 4 in-situ measurements, probably more by the date of the conference. (Work on going, no feedback yet from the Conference Organizers)

Project applications

FPA 2019-2021: a service has been proposed in July 2018 for the application to Framework Partnership Agreement (FPA) of Copernicus. This action will support the dissemination of the activity toward the community via the organisation of training courses and workshops.
(Feedbacks from application planned on June 2019)

Horizon 2020:
Call: H2020-SC5-2018-2019-2020 (Greening the economy in line with the Sustainable Development Goals (SDGs)
Topic: SC5-16-2019
Type of action: IA
Proposal number: SEP-210573487
Proposal acronym: ExtendSolar
8 services have been proposed, 1 is about PAR.
(Feedbacks from application planned on June 2019)

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Steps of developments

(reverse chronological order)

29 Nov. 2017: rdv au CIEMAT. Discussion with the team about spectral developments

Oct. 2017: McClear v2 to McClear v3 => Stéphane is checking if ok. Correction of compute_gc_mcclear to correct the use of E0 (broadband instead of Kato)

Sept. 2017: McClear in real time

Aug. 2017: Self validation and first delivery of spectral radiation datasets to a user. Validation against in situ measurements is not yet carried out.

July: Bug in McClear v2 (change of atmospheric profile during the day generating sharp steps of radiation values). This has been corrected during the maintenance operation that occurred on 31st July 2017 (information not available in the release not as it impacted only the spectral data which is not an operational service).

Spring 2017: First developments of a precursor of service in Matlab following the work of William

2016 and before: research carried out by William Wandji, a PhD student from MINES ParisTech


Monthly and daily PAR from 2000-2016 :
Result from a radiation model transfer + neural networks with forcings from MODIS atmospheric products

Huete et al (2002) explique que l'indice EVI est plus adapté pour décrire l'activité photosynthétique des forêts tropicales (high-biomass forests) que le NDVI. (See Wikipedia for EVI - the values of coefficients for MODIS-EVI algorithm are; L=1, C1 = 6, C2 = 7.5, and G (gain factor) = 2.5)

PAR sensor, PSQ1 INRA Bornet June 2018: "A standardised PAR spectral response in the visible light range between 400nm and 700nm wavelength was defined by McCree (1972) such that each photon within this region is equally absorbed. ‘Blue' photons of shorter wavelength (higher frequency) have more energy than ‘Red' photons of longer wavelength. The amount of PAR is commonly expressed as Photosynthetic Photon Flux Density (PPFD) with a unit of µmol/m²·s."

Need for an online tool to convert µmol/m2/s into W/m2 or Wh/m2.

[le stress des plantes soumises à des grandes variabilités temporelles de l'éclairement solaire]

Proposition of division of the visible spectral by Dario: (not compliant with  ISO 21348 Definitions of Solar Irradiance Spectral Categories)

  • blu-violette, (400-490 nm),
  • green (490-560 nm),
  • yellow (560-590 nm);
  • red-orange (590-700 nm)   

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