overview of prospect and sail model 2nd ir/microwave emissivity group meeting noaa/nesdis/star...
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Overview of PROSPECT and SAIL Model
2nd IR/Microwave emissivity group meeting
NOAA/NESDIS/STAR
2008.08.01
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Introduction of PROSPECT
PROSPECT is a radiative transfer model that represents the optical properties of plant leaves from 400 nm to 2500 nm.
The key parameters in the model are leaf structure parameter (N), chlorophyll a+b (Cab) and the equivalent water thickness (Cw) .
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transmitted + emitted
absorb
ed
PROSPECT- Leaf Optical Properties Spectra MODEL
reflected + emitted
S.Jacquemoud and F.Baret, REMOTE SENS. ENVIRON.34:75-91(1990)
depend on anatomical leaf structure andbiochemical leaf composition
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i
iiCkK
Description of the PROSPECT model
Nidenticallayers
Is
Elementary layer:n: refractive indexK: global absorption coefficient
Surface effects
Hemispheric fluxes
Global absorption:
Specificabsorptioncoefficients
Content inabsorbingmaterial
reflectance
()
() transmittance
(A.Olioso, S.Jacquemoud ,F.Baret , Adaptation of the leaf optical property
model PROSPECT to thermal infrared, 2006)
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N leaf structure parameterCab chlorophyll a+b concentration (g.cm2)Cbp brown pigment concentration (g.cm2) Cw equivalent water thickness (cm)Cm dry matter content (g.cm2)
PROSPECT INPUTS
PROSPECT OUTPUTS
R()T()
– leaf reflectance – leaf transmittance
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Comparison of two different version1998 version3.01
1995 version 2.01
Cw=0 Cw=0.002
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PROSPECT V3.01 outputs under Cw from 0.0 to 0.02 cm-1
(0.0,0.0002, 0.0011, 0.0065, 0.0155, 0.02 cm-1)
0.0
0.02
N = 1.5, Cab = 50 g.cm2, Cdm = 0.005 g.cm2
0.02
0.0
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Energy balance
Kirchhoff’s Law
The emissivity of a body equals its absorptivity at thermal equilibrium
1 ATR
So, absorptivity = emissivity ???
One question ?
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Sensitivity of the Leaf Structure Parameter N
N=1~1.5 Albino maize leaf and monocotyledons with compact
mesophyllN=1.5~2.5 Dicotyledons by a spongy parenchyma with air
cavities on the abaxial faceN>2.5 Senescent leaves with a disorganized internal
structure
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Cw=0, N=1.0,1.5,2.0,2.5,3.0
3.0
2.5
2.0
1.5
1.0
Visible light Region
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Cw=0.02, N=1.0,1.5,2.0,2.5,3.0
3.0
2.5
2.0
1.5
1.0
400,690,1450,1950,2500
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reasonable
Non-reasonable
In fact, N=3 ,represents senescent leaves with disorganized structure, the Cw should be small even it is zero. So the combination given parametersof Cw=0.02 and N=3 should be non-reasonable. Relatively, the Cw=0.0 and N=3 will be a better choice.
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Questions:
The key point is how to determine the value of the combination inputs parameters.
What is the relationships between inputs parameters realistically?
(N, Cab, Cw,Cm,Cbp)
Need in-situ data and satellites data validation
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Scattering by Arbitrarily Inclined Leaves-SAIL Model
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Introduction
The scattering and extinction coefficients of SAIL model are derived for the case of arbitrary leaf inclination angle and a random leaf azimuth distribution.
SAIL Model includes the G.H.Suits uniform model.
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Canopy Layer Morphology Characteristics
The idealized morphology of a canopy layer assumed for the SAIL Model is given as following:
The layer is horizontal and infinitely extended The only canopy components are small and flat
leaves The layer is homogenous
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bi-directional reflectance
directional-hemispherical reflectance
soil surface
plant canopy
SAIL model (Verhoef 1984-1985)
sun
absorption of directionalincoming radiation
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SAIL Model parameters
LAI mean leaf angle (θl) leaf reflectance (ρl) leaf transmittance (τl) soil reflectance (ρs) geometry of observation Sun position
spectral reflectances absorption of solar
radiation
Inputs
Outputs
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W.VERHOEF, (1984),Remote sensing of Environment,16:15-141
Bidirectional reflectance profiles in the green(550nm)
SAIL Model Suits ModelH=1.000
V=1.571
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W.VERHOEF, (1984),Remote sensing of Environment,16:15-141
Bidirectional reflectance profiles in the near infrared
SAIL Model Suits ModelH=1.000
V=1.571
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Conclusions
The SAIL Model is an improved version of Suits’s canopy reflectance model
The extinction and scattering coefficients in the Suits’s Model are calculated on the basis of a given LAI and leaf inclination distribution
The calculation of canopy reflectance is the same both models, the uniform Suits model is included as a special case
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Next to do
As a very important aspect is try to understand how to exactly determine the inputs parameters for these two models
Understand the optical parameters calculation and details theory in the model