Towards an operational method for estimating Photosynthetically Active Radiation in clear-sky conditions on the Earth s surface

Transcription

1 Département Énergétique et Génie des Procédés Centre Observation, Impacts, Energy (O.I.E.) June 25th, 2015 Towards an operational method for estimating Photosynthetically Active Radiation in clear-sky conditions on the Earth s surface William WANDJI, Philippe BLANC and Lucien WALD william.wandji@mines-paristech.fr ICEM

2 o What is PAR? PAR stands for Photosynthetically Active Radiation Basic photosynthesis Biomass and energy 2

3 o What is PAR? Clear sky PAR depend of aerosol properties (AOD), total water column (H2O), ground surface (ground albedo), etc 3

4 o What is PAR? Spectral response PAR is an irradiance (W m -2 ) PAR is also photosynthetically photon flux density PPFD (µmol m -2 s -1 ) Both units are linked by the widely used approximation 1 W m µmol m -2 s λ (nm) 700 PAR α I λ SR λ dλ 400 4

5 o How to estimate PAR? PAR measurements are rare in space and time Alternative way is to use Radiative Transfer Model Atmospheric state (AOD, H2O, ground albedo, ) Radiative Transfer Model Detailed spectral calculations (~300 spectral calculations) PAR radiation [400; 700] nm Slow direct path 5

6 o How to estimate PAR? Atmospheric state (AOD, H2O, ground albedo, ) The k-distribution method and correlated-k approximation Kato et al. (1999) (only 12 spectral calculations) PAR radiation [400; 700] nm Faster path DAK, libradtran, RAPRAD, SPECMAGIC o 12 spectral calculations between 363 nm and 704 nm for PAR-band (400 nm and 700 nm) W., Wandji Nyamsi, B., Espinar, P., Blanc, and L., Wald: 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, 23, ,

7 o Problem statement Spectral response 12 spectral bands #6 452 Kato bands (KB) # 667 #7 # #16 λ (nm) Photosynthesis band o But λ (nm) 7

8 o Resampling technique 8

9 o Resampling technique KT nm = KT KB

10 o Resampling technique 10

11 o Resampling technique 11

12 o Resampling technique 19 affine functions selected : KT i = a i KT KBj + b i 12

13 o Resampling technique Linear interpolation and extrapolation 13

14 o Resampling technique In general, there is a good agreement of the technique over PAR-band 14

15 o Overview of planned operational method Atmospheric properties for clear sky conditions (MACC-II project) Aerosol properties LUT with Kato et al. approach + Resampling technique Ozone Water vapor Ground albedo (MODIS) PAR albedo 0.47 total albedo Atmospheric state Photosynthetically Active radiation 15

16 o Ground measurements stations SURFRAD and NREL networks : PPFD measurements Data are available freely online June 2015 ICEM

17 o Validation of the method Boulder, [N40.12, W105.23, alt=1689 m] Bias = -13 rbias= -1 % RMSE=45 rrmse=3 % Mean=1262 CC= points June 2015 ICEM

18 o Validation of the method Boulder, [N40.12, W105.23, alt=1689 m] Bias = -13 rbias= -1 % RMSE=45 rrmse=3 % Mean=1262 CC= points June 2015 ICEM

19 o Validation of the method Desert Rock, [N36.62, W116.02, alt=1007 m] Bias = -69 rbias= -5 % RMSE=92 rrmse=6 % Mean=1421 CC= points June 2015 ICEM

20 o Validation of the method Desert Rock, [N36.62, W116.02, alt=1007 m] Bias = -69 rbias= -5 % RMSE=92 rrmse=6 % Mean=1421 CC= points PAR-albedo = total albedo should be 0.84 for fine rocks June 2015 ICEM

21 o Conclusions and perspectives In general, good level of accuracy of the method ( rbias < 5%, rrmse < 7%, R >0.96) Establishing an accurate determination of PAR-albedo Including the attenuation of clouds and performing experimental validation in all-sky Performing validation on direct PAR Various applications of the operational chain for the determination of luminous efficacy, UV fluxes and PV performance studies Articles related to this study: (1) Wandji Nyamsi, W., Espinar, B., Blanc, P., and Wald, L.: How close to detailed spectral calculations is the k-distribution method and correlated-k approximation of Kato et al. (1999) in each spectral interval?, Meteorol. Z., 23, , 2014, doi: /metz/2014/0607 (2) Wandji Nyamsi, W., Espinar, B., Blanc, P., and Wald, L.: Estimating the photosynthetically active radiation under clear skies by means of a new approach, Adv. Sci. Res., 12, 5-10, doi: /asr ,

22 Thank you for your attention! William Wandji PhD student 6/24/2015 MINES ParisTech, Centre O.I.E. 22