1/16 4D modeling of canopy architecture for improved characterization of state and functionning F. Baret INRA-CSE Avignon

2/16 Introduction The description of vegetation architecture is one of the main limiting factor in the estimation of canopy characteristics such as LAI Importance of the temporal dimension that drives the generation of canopy architecture and that offers regularities to be exploited Turbid mediumGeometricExplicit

3/16 Requirements Good dynamic description of canopy architecture Low amount of parameters/variables (for better retrieval) Fast computation of the radiative transfer Objectives of the study Illustrate how canopy structure evolution could be generated Present the corresponding variables and parameters used Describe how to compute the radiative transfer Conclude on the work to achieve

4/16 The context of high spatial and temporal resolution observations High spatial resolution: –Generally ‘pure’ pixels –object observed could be identified in terms of species High temporal resolution –Continuous monitoring to be exploited in the understanding of how the architecture builds up (or destroys down!) Case illustrated here: maize canopies with relatively simple and well known architecture

5/16 Modeling maize canopies architecture Work derived from previous studies : M. Espana, B. Andrieu, M. Chelle, B. Koetz, N. Rochdi Describing the time course of individual leaves and stems Based on a series of experiments Semi-mechanistic models Reduced number of variables Reasonable level of details in canopy architecture description

6/16 T0T1T2 Level of canopy architecture details required for reflectance simulation

7/16 Leaf area time course Time of leaf of order n: Apparition : n*DTc Disparition : n*DTc+DTs Variables required: N_max S_max To DTc DTs

8/16 Other architecture characteristics Canopy –Plant density –Distance between rows –Row azimuth Plant –Leaf insertion height –Leaf shape/curvature –Leaf azimuth –Leaf zenith Leaf order Leaf insertion height

9/16 Properties of the 4D maize model Limited number of variables/parameters: –N_max –S_max –To –DTc –DTs –H_max –Density –Leaf inclination Dynamics well described Improvements –Leaf curvature (easy) –Better senescence including keeping senescent leaves –Variability between plants (size, position, …) –Flowers/ears –Vertical gradients in chlorophyll

10/16 Regularities in Chlorophyll gradients Distribution verticale du contenu en chlorophylle mesurée à partir de l’instrument SPAD

11/16 From canopy architecture … to reflectance Parcinopy Multispectral version now available (M. Chelle, V. Rancier)

12/16 Decomposing radiative transfer  ss =a  ss  oo.  so =f  so =d+e  dd =c/(a.R s +b.R s )  sd =b  do =g /(a.R s +b.R s ) n(level,way,direction,inter_sol,inter_veget)=n umber of photons (radiance) level: b=bottom; t=top way: - = downward; + = upward direction:  s=sun direction;  v=view direction;h=hemispheric interaction order (inter_sol, inter_veget): 0: no interaction 1: 1 interaction only  1: one or more interactions Terms required R c =  so +  ss  oo.R s +((  ss.R s +  sd.R s ).  do +(  sd +  ss.R s.  dd ).R s.  oo )/(1-R s.*  dd ) Black soil term Soil interaction term 4 fluxes approximation

13/16 Vegetation contribution (  so )  so = f(  leaf,  leaf,P(LAI,ALA,S,D, ,  s  v)) Parameters 'P' are spectral invariants

14/16 Approach [LAI,ALA,S,D,  ] Distribution of input variables Construction of the 3D architecture [  s  v ] Sun/view configuration PARCINOPY RT components [  l,  l ] leaf reflectance & Transmittance Building a parametric model Parametric model P(LAI,ALA,S,D, ,  s  v,  l,  l ) [  s ] Soil reflectance Canopy reflectance

15/16 CONCLUSION A more mechanistic/realistic approach is proposed –Based on a ‘simple’ description of canopy architecture to use fewer variables –No need for continuous description (discrete is enough) –Needs sensitivity analysis to evaluate the influence of the variation of N_max, H_max, … –Needs full (or at least parametric for the spectral aspect) parametric model to be implemented to compute the reflectance fields –Needs coupling to canopy functioning models

16/16 Coupling between structure and function models 4D Architecture Model LAI Reflectance  T Stress (H2O, N) Initialization Work in progress for exploitation within an assimilation scheme, …