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A.Olioso, S. Jacquemoud* & F. Baret UMR Climat, Sol et Environnement INRA Avignon, France * Institut...
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Transcript of A.Olioso, S. Jacquemoud* & F. Baret UMR Climat, Sol et Environnement INRA Avignon, France * Institut...
A.Olioso, S. Jacquemoud* & F. Baret
UMR Climat, Sol et EnvironnementINRA Avignon, France
* Institut de Physique du Globe de Paris (IPGP)Département de Géophysique Spatiale et Planétaire
Université Paris 7 - Denis Diderot
Adaptation of the leaf optical property model PROSPECT to
thermal infrared
Radiative properties of leaves in the thermal infrared are required for implementing radiative transfer models
ex: => remote sensing studies => fire propagation studies
Model of leaf properties are required for
=> analysing variations of leaf properties (ex. with leaf moisture) => linking leaf properties to plants processes
There is no such model !
=> building a model on the basis of the PROSPECT model (Jacquemoud and Baret 1990) which is working in the solar domain
transmitted + emitted
absorb
ed
Leaf optical properties
reflected + emitted
depend on anatomical leaf structure andbiochemical leaf composition
i
iiCkK
Description of the PROSPECT model
Nidenticallayers
Is
Elementary layer:n: refraction indexK: global absorption coefficient
Surface effects
Hemispheric fluxes
Global absorption:
Specificabsorptioncoefficients
Content inabsorbingmaterial
reflectance
()
() transmittance
NCab
Cbp
Cw
Cdm
PROSPECT
()()
leaf structure parameterchlorophyll a+b concentration (g.cm2)brown pigment concentration (g.cm2) equivalent water thickness (cm)dry matter content (g.cm2) N = 1.5, Cab = 50 g.cm2, Cdm = 0.005 g.cm2
PROSPECT
PROSPECT INPUTS
N - Number of layers
Cab - Chlorophyll a+b content
Cbp - Brown pigment content
Cw - Equivalent water thickness
Cdm - Dry matter content
n(λ) - Refractive index
ki(λ) - Specific absorption coefficients of constituants
() – leaf reflectance() – leaf transmittance
PARAMETERS
between 0.4 and 2.5 µm
PROSPECT OUTPUTS
PROSPECT INPUTS
N - Number of layers
Cab - Chlorophyll a+b content
Cbp - Brown pigment content
Cw - Equivalent water thickness
Cdm - Dry matter content
n(λ) - Refractive index
ki(λ) - Specific absorption coefficients of constituants
() – leaf reflectance() – leaf transmittance
PARAMETERS
between 0.4 and 2.5 µm
PROSPECT OUTPUTS
ε () – leaf emissivity
kw(λ) kdm(λ)
between 2.5 and 18 µm
* specific absorption coefficient of dry matter: kdm(λ)
-> no info available at the moment
-> to be obtained by inverting PROSPECT against leaf spectrum data (in particular from dry leaf)
* idem for leaf layer refractive index n(λ) (inversion from fresh leaf spectra)
* N, Cw, Cdm may be obtained from library, measurements or from PROSPECT inversion between 0.4 and 1.8 µm
PROSPECT INPUTS
DETERMINATION OF PROSPECT INPUTS:
the only easily available data that made it possible to determine PROSPECT inputs were found in the ASTER spectral library
Solar domain Thermal infraredN, Cw, Cdmkdm(λ), n(λ)
Specific absorption coefficient of dry matter: kdm(λ)
inversion of PROSPECT against ‘ASTER’ dry spectra
result of inversion compared to cellulose and lignin spectra
0.4-2.5 µm
some cellulose and lignin features
but not always specific
Lignin
Specific absorption coefficient of dry matter: kdm(λ)
comparison to water
Difficult zone becauseof high absorption of bothdry matter and H2O
Low absorption zone
Opposite behavior of H2O and dry matter
Determination of the refractive index : n(λ)
inversion of wet spectra gave refrative index
Lowest absorptionzone
COMPARISON OF PROSPECT OUTPUTS / MEASUREMENTS
Data from
-ASTER spectral library -Salisbury and D’Aria 1992
-MODIS spectral library
Sensitivity to leaf water content
sensitivity to Cw from 0.0002 cm-1 to 0.0512 cm-1
(0.0002, 0.0008, 0.0032, 0.0128, 0.0512 cm-1)
0.0002
0.0512High transmittance
Sensitivity to leaf water content
sensitivity to Cw from 0.0002 cm-1 to 0.0512 cm-1
(0.0002, 0.0008, 0.0032, 0.0128, 0.0512 cm-1)
Sensitivity to leaf water content
sensitivity to Cw from 0.0002 cm-1 to 0.0512 cm-1
(0.0002, 0.0008, 0.0032, 0.0128, 0.0512 cm-1)
0.0512
0.0002
Emissivity lower than expected fromreflectance
Sensitivity of 8-14 µm emissivity to leaf moisture
fresh leaves and dry leaves don’t have the same internal structure (parameter N = 2 and 4)
different responses average behaviour in situ ?
Sensitivity to leaf surface properties
various components (silica, waxes…) and / or structure (hair, epidermis cell shape…) may affect leaf surface – radiation interactions
introduction of new components use the radiation incident angle of the plate model (set to 59° usualy)
10°
90°
sensitivity to incident angle from 10 to 90° by step of 10°
Conclusion
Encouraging first results
There is a lot of work still to do
acquisition of leaf data for calibrating and testing the model
analysis of the effects of the various components in order to discriminate generic effects and specific effects
investigation of leaf surface effects
investigation of leaf drying impact…
….
implementation in canopy radiative transfer model for the analysis of land surface emissivity spectra acquired from TIR multispectral sensors