Prsentation PowerPoint

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Test of the SAIL-Thermique radiative transfer
model for simulating thermal infrared emissivity
and emissivity spectra of plant canopies Albert
Olioso (1), José Sobrino (2), Guilhem Soria (2),
Michaël Chelle (3), Benoit Duchemin (4),
Frédéric Jacob (5) (1) INRA/CSE, Avignon,
France. (2) University of Valencia, Spain. (3)
INRA, Thiverval-Grignon, France. (4) CESBIO,
Toulouse, France. (5) ESA Purpan, Toulouse,
France.
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Introduction
Models of radiative transfer (RT) inside a
vegetation canopy may be used for simulating
land surface emissivity ex Anton and Ross
1990, Olioso 1992, Snyder and Wan 1998 However,
(almost?) no RT model was already evaluated
against emissivity measurements Evaluation only
by comparison to other models. ex François et
al. 1997, Guillevic et al. 2003, Sobrino et al.
2005
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SAIL model (Verhoef 1984-1985)
sun
bi-directional reflectance
directional-hemispherical reflectance
absorption of directionalincoming radiation
plant canopy
soil surface
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SAIL model (Verhoef 1984-1985)
sun
bi-directional reflectance
directional-hemispherical reflectance
absorption of directionalincoming radiation
plant canopy
soil surface
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SAIL model (Verhoef 1984-1985)
sun
bi-directional reflectance
directional-hemispherical reflectance
absorption of directionalincoming radiation
plant canopy
soil surface
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(No Transcript)
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Simulations with SAIL-Thermique
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• Test of the model
• Available database including ground measurements
  of land surface emissivity
• - DAISEX experiment in Barrax (Spain, 1998-2000)
  
• Alpilles-ReSEDA experiment near Avignon (France,
  1997)
• Specific experiment
• WATERMED experiment in Marrakech (Morocco ,
  2003)
• Bibliographic data
• van de Griend and Owe IJRS 1993 (Bostwana)
• Valor and Caselles RSE 1996 (South-East France)
• Sugita et al. AFM 1996 (Tsukuba, Japan)
• All measurements done using the box method

University of Valencia groups
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Test of the model
(barley, alfalfa, corn, sugar beet)
(wheat, alfalfa)
(wheat, barley, weeds)
(wild grass, sorghum, shrubs)
(wild grass, alfalfa, shrubs)
(mixed pasture)
library ? bibliography ?
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Test of the model Available database with leaf
optical properties (usually expressed as leaf
emissivity) - ASTER spectral libray - MODIS
spectral library Bibliographic sources - Fuchs
and Tanner 1966 - Idso et al. 1969 - Wang et al.
1994 - Coll et al. 2001 Various methods of
measurements
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Analysis of leaf emissivity data (8-14 µm)
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• Test of the model / measurements
• no dataset have all required data
• stochastic simulations based on a priori data
  distributions
• - leaf properties (emissivity) normal
  distribution with
  mean 0.971 and std 0.011
• - mean leaf angle uniform distribution 45 -
  70
• - LAI uniform 0 6
• - direction of observation nadir

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Alpilles Barrax (8-14 µm)
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van de Griend and Owe 1993 (8-14 µm)
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Valor and Caselles 1996 (8-14 µm)
Sugita et al. 1996 (8-14 µm)
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Marrakech 2003 (8-13 µm)
DRY CONDITIONS
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All data together simulation for mean values
(leaf emissivity 0.97, spherical canopy)
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No shrubs and no dry data simulation for mean
values
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Simulation of emissivity spectra

• SAIL-Thermique is a monospectral model
• but it may be used for simulating emissivity at
  any TIR wavelength as soon as leaf and soil
  spectral properties are known

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Simulation of emissivity spectra
LAI1
LAI0.5
LAI0
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Simulation of emissivity spectra
LAI0
LAI0.5
LAI1
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Simulated multispectral emissivity vs.
measurements data over dried barley in
Marrakech (CIMEL 4 channels)
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Impact of leaf drying

• Spectra simulations showed that emissivity may be
  low for dried plants
• This is confirmed by some in-situ measurements at
  the canopy level in Barrax and in Marrakech

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All data together simulation for mean values
(leaf emissivity 0.97 (wet) and 0.91 (dry),
spherical canopy)
All data rmse was 0.009 and no shrubs and no
dry data rmse was 0.005
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Impact of leaf drying evolution of emissivity
along the crop cycle
Two leaf moisture - emissivity models
Evolution of plant characteristics of a wheat crop

• Application of SAIL-Thermique with two vegetation
  layers
• green layer (wet leaves)
• senescent layer (drying leaves) below the green
  layer

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Impact of leaf drying evolution of emissivity
along the crop cycle
Leaf model 1
Leaf model 2
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Alpilles wheat data
Barrax stubble data
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• Some conclusions
• Emissivity simulations with the SAIL-Thermique
  model compare
• favourably with experimental data
• (more tests will be done in the future)
• The model might be used for analysing TIR
  multispectral data
• in a direct mode for analysing spectrum
  variations
• in an inverse mode for deriving plant component
  spectra
• The model was designed for being integrated in
  Soil-Vegetation -Atmosphere Transfer models and
  implementing assimilation procedures in the
  thermal infrared together with solar and
  microwave
• data
• We have to go further in understanding leaf
  optical properties in
• the thermal infrared domain (e.g. response to
  drying)