SIMULATION OF ALBEDO AT A LANDSCAPE SCALE WITH THE D.A.R.T. MODEL

1. 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

2. 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 Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Methodology • Field measurements over an agricultural area • High resolution imagery (SPOT HRV data) • DART tool simulations of remote sensing images

3. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Outline • TheDARTmodel • Thestudyarea • InputDARTparameters • Land cover map • LAI • Soils optical properties • Leaves optical properties • Landscapesimulations • Results • Conclusions • Mainprospects

4. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 THE DART model TheD.A.R.Tmodel Discrete 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

5. Opaquecells Soil, water surfaces, urban elements, trunks  surface scattering Turbidcells Vegetation, air  volume scattering LAD LAI ,  Plane opaque surfaces: parametric reflectance models DART images, nadir view (green, red & NIR spectral bands) Sylvie DUTHOIT Workshop on Albedo Products, April 2005 THE DART model

6. Optical and structural parameters Land cover map Leaves 2: LAI2, LAD2, 2, 2 Leaves 1: LAI1, LAD1, 1, 1 Leaves 3: LAI3, LAD3, 3, 3 soil Plots mosaïc Sylvie DUTHOIT Workshop on Albedo Products, April 2005 THE DART model “DART - Landscape”release Each plot is homogeneous (randomly distributed leaves)

7. 6x6 km and 3x3 km Sylvie DUTHOIT Workshop on Albedo Products, April 2005 The study area An agricultural study area: Lamasquère

8. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 The study area • 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

9. SPOT 2004 images Land cover map (Gouaux, Ducrot, CESBIO) DART input parameter Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Input DART parameters Landcovermap

10. Wheat Soya Corn Sunflower Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Input DART parameters DestructivePAImeasurements

11. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Input DART parameters SeasonalevolutionofthePAI Grassland = SMOSRex measurements (KerrY., CESBIO)

12. PAI 7 0 Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Input DART parameters Spatialisation of the LAI Vegetation index/LAI relation SPOT images - corrected from atmospherical effects (SMAC model). - inter-calibrated (G. Dedieu, CESBIO)

13. Measurements on plowed, sowed, dry and wet bare soils Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Input DART parameters Soilsopticalproperties 2 major types of soils on the area (INRA database) « Terreforts » « Boulbènes»

14. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Input DART parameters SoilsBRDFmeasurements Spectroradiometer ASD Directional measurements in several view angles Hapke model to simulate the bi-directionnal reflectance > parameters in the DART model

15. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Input DART parameters Leavesopticalproperties ASTER database

16. SPOT reflectance Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Landscape simulations LANDSCAPESIMULATIONS ComparisonswithSPOTreflectances • 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%

17. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Landscape simulations FIRSTRESULTS Comparisons SPOT/DART values Dry soils

18. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 Landscape simulations Comparisons SPOT/DART values Dry soils and wet soils Dry soils Wet soils

19. 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 Sylvie DUTHOIT Workshop on Albedo Products, April 2005 CONCLUSIONS Results are encouraging The seasonnal evolution is well reproduced, in general

20. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 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. - Follow up of the work with new simulations for 2005 - Comparison with SEVIRI products - Evaluation in the framework of the SAF-Land project. • DART: professional release (CNES, 2005), freely available for scientists

21. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 THANK YOU !

22. Sylvie DUTHOIT Workshop on Albedo Products, April 2005 MODIS Black-sky albedo