Overview of PROSPECT and SAIL Model

2nd IR/Microwave emissivity group meeting

NOAA/NESDIS/STAR

2008.08.01

Bo Qianbqian@umd.edu

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) .

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

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)

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

Comparison of two different version1998 version3.01

1995 version 2.01

Cw=0 Cw=0.002

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

Energy balance

Kirchhoff’s Law

The emissivity of a body equals its absorptivity at thermal equilibrium

1 ATR

So, absorptivity = emissivity ???

One question ?

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

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

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

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.

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

Scattering by Arbitrarily Inclined Leaves-SAIL Model

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.

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

bi-directional reflectance

directional-hemispherical reflectance

soil surface

plant canopy

SAIL model (Verhoef 1984-1985)

sun

absorption of directionalincoming radiation

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

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

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

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

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