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SIMULATION OF ALBEDO AT A LANDSCAPE SCALE WITH THE D.A.R.T. MODEL AN EFFICIENT TOOL FOR EVALUATING COARSE SCALE SATELLITE PRODUCTS?. Sylvie DUTHOIT*, Valérie DEMAREZ* Jean-Philippe GASTELLU-ETCHEGORRY*, Emmanuel MARTIN* Jean-Louis ROUJEAN**. * CESBIO, ** Météo-France. - PowerPoint PPT Presentation
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SIMULATION OF ALBEDO AT A LANDSCAPE SCALE WITH THE D.A.R.T. MODEL
AN EFFICIENT TOOL FOR EVALUATING COARSE SCALE SATELLITE PRODUCTS?
Sylvie DUTHOIT*, Valérie DEMAREZ*Jean-Philippe GASTELLU-ETCHEGORRY*, Emmanuel MARTIN*
Jean-Louis ROUJEAN**
* CESBIO, ** Météo-France
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
• Field measurements over an agricultural area
• High resolution imagery (SPOT HRV data)
• DART tool simulations of remote sensing images
Measurements over a long time period with good spatial sampling
+ Simulations of remote sensing images with DART
Spatial and temporal dynamic of the BRDF and albedo
Methodology
• The DART model
• The study area
• Input DART parameters• Land cover map• LAI • Soils optical properties• Leaves optical properties
• Landscape simulations• Results• Conclusions
• Main prospects
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
Outline
The D.A.R.T modelDiscrete Anisotropic Radiative Transfer
(Gastellu et al., 1996; 2005)
Principe
• Ray tracing method
• Discrete ordinate technique
(space and directions)
• Matrix of parallelepipedic cells
• With/without atmosphere, topography
Products
• Reflectance and temperature products (directional images)
• Radiative budget products (incident, intercepted, absorbed, scattered radiation for each scene level)
• Atmospheric products
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
THE DART model
Opaque cellsSoil, water surfaces, urban elements, trunks
surface scattering
Plane opaque surfaces: parametric reflectance models
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
DART images, nadir view (green, red & NIR spectral bands)
Turbid cellsVegetation, air volume scattering
LADLAI
THE DART model
“DART - Landscape” release
Optical and structural parameters
Leaves 1: LAI1, LAD1, 1, 1
Leaves 2: LAI2, LAD2, 2, 2
Leaves 3: LAI3, LAD3, 3, 3
soil
Land cover map
Plots mosaïc
Each plot is homogeneous (randomly distributed leaves)
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
THE DART model
An agricultural study area: Lamasquère
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
The study area
6x6 km and 3x3 km
•For the study area, DART need:
• Land cover map of the area
• Mean PAI of each stand
• Informations about canopy structure
• Leaves optical properties
• Soils optical properties
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
The study area
Land cover map
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
SPOT 2004 images
Land cover map(Gouaux, Ducrot, CESBIO)
DART input parameter
Input DART parameters
Wheat
Corn
Soya
Sunflower
Destructive PAI measurements
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
Input DART parameters
0
2
4
6
8
80 130 180 230Julian day
PAI
Corn Sunflower Soybean Wheat grassland
Seasonal evolution of the PAI
Grassland = SMOSRex measurements (KerrY., CESBIO)
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
Input DART parameters
y = 0,0017e8,9153x
R2 = 0,8774
0
1
2
3
4
5
6
7
8
0,5 0,6 0,7 0,8 0,9 1
MSAVI
PA
I
Spatialisation of the LAI
Vegetation index/LAI relation
SPOT images- corrected from atmospherical effects (SMAC model).- inter-calibrated(G. Dedieu, CESBIO)
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
7
0
PAI
Input DART parameters
2 major types of soils on the area (INRA database)
Soils optical properties
« Terreforts »« Boulbènes»
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
Measurements on plowed, sowed, dry and wet bare soils
Input DART parameters
Soils BRDF measurements
Spectroradiometer ASD
Directional measurements in several view angles
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
Hapke model to simulate the bi-directionnal reflectance
> parameters in the DART model
Input DART parameters
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
Leaves optical properties
0
10
20
30
40
50
60
70
0,4 0,5 0,6 0,7 0,8 0,9 1
Wave lenght
Re
fle
cta
nc
e (
%)
grass decidious species
ASTER database
Input DART parameters
April 21, May 16 and July 17
• Illuminations configurations for the time (date and hour) of the images
• 3 spectral bands (0.5-0.59, 0.61-0.68 and 0.79-0.89 m)
• diffuse radiation 20%
LANDSCAPE SIMULATIONSComparisons with SPOT reflectances
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
0
0,1
0,2
0,3
0,4
110 130 150 170 190 210Julian dayGreen Red NIR
SPOT reflectance
Landscape simulations
FIRST RESULTS
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
NIR (0,79-0,89 m)
0,26
0,28
0,3
0,32
0,34
0,36
0,38
100 120 140 160 180 200 2200
5
10
15
20
25
30
35
1 8
15
22
29
36
43
50
57
64
71
78
85
92
99
10
6
11
3
12
0
da
ily p
rec
ipit
ati
on
s (
mm
)
APRIL MAY JUNE JULY
Comparisons SPOT/DART valuesDry soils
Landscape simulations
Green( 0,5-0,59 m)
0,03
0,06
0,09
0,12
100 120 140 160 180 200 220
Red (0,61-0,68 m)
0,06
0,09
0,12
0,15
100 120 140 160 180 200 220
Julian day
Ref
lect
ance
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
Comparisons SPOT/DART values Dry soils and wet soils
Dry soils
Wet soils
Landscape simulations
Green (0.5-0.59)
0,04
0,06
0,08
0,1
0,12
100 120 140 160 180 200 220
Julian day
Re
fle
cta
nc
e
NIR (0.79-0.89)
0,2
0,24
0,28
0,32
0,36
0,4
100 120 140 160 180 200 220
Red (0.61-0.68)
0,04
0,06
0,08
0,1
0,12
0,14
100 120 140 160 180 200 220
CONCLUSIONS
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
BUT the difference between simulations and SPOT reflectance values are not negligible:
1- soils optical properties for wet soils (rain, irrigation in july)measurements in progress on the area
2- leaves optical properties : different for each crop species AND seasonnal evolution PROSPECT simulations
Results are encouragingThe seasonnal evolution is well reproduced, in general
PROSPECTS…
• Stand scale validation - Directionnal reflectance measurements over crops canopies
(ASD instrument) - Albedo measurements (K&Z net radiometer) over 2 crops stands
• Landscape scale simulations - Comparison with SPOT 3x3 km and 6x6 km. - Comparison with MODIS products: Black-sky albedo (16 days), Nadir- adjusted reflectance.
Sylvie DUTHOIT Workshop on Albedo Products, April 2005
• DART: professional release (CNES, 2005), freely available for scientists
- Follow up of the work with new simulations for 2005
- Comparison with SEVIRI products - Evaluation in the framework of the SAF-Land project.