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Photo: Doug Parker Use of FORMOSAT images over the Gourma site (Mali) E. Mougin, V. Demarez, P. Hiernaux, L. Kergoat, V. Le Dantec, M. Grippa, Y. Auda,

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Presentation on theme: "Photo: Doug Parker Use of FORMOSAT images over the Gourma site (Mali) E. Mougin, V. Demarez, P. Hiernaux, L. Kergoat, V. Le Dantec, M. Grippa, Y. Auda,"— Presentation transcript:

1 Photo: Doug Parker Use of FORMOSAT images over the Gourma site (Mali) E. Mougin, V. Demarez, P. Hiernaux, L. Kergoat, V. Le Dantec, M. Grippa, Y. Auda, F. Timouk

2 The study site FORMOSAT data Field data Applications Content

3 The AMMA Gourma site mean = 373 mm Short rainy season : JJAS High rainfall variability High aerosol loading A Sahelian climate. Characterized by large homogeneous surfaces. Dedicated to satellite product validation Soil moisture - albedo, Radiation, Ts - LAI, FAPAR, NPP A pastoral Sahelian site

4 The Hombori site (15.3°N, 1.6°W) AERONET photometer Radiometer / PAR sensor

5 The Gourma land units Shrub Savannah Open forest Flooded plains LAI : LAI : LAI : 2 - 4

6 The Gourma land units PondErosion surface Tiger bush Millet field LAI : < 0.1 LAI :

7 Sand dunes Open forest Erosion surface 60 km Tiger bush Ponds SPOT- HRV image Monitoring site Agoufou

8 July 15 May 29June 06 July August 20 August 19 A strong seasonal dynamics and a high inter annual variability of vegetation cover July 16 June 08 August 23

9 July 05August 26July 28 July 02 August 27September 16 Seasonal dynamics of acacia forests and millet fields

10 Field data : LAI, FCover, FAPAR Use of hemispherical photographs

11 Field data : LAI, FCover, FAPAR (trees) Isolated trees Open Acacia forest : 500 m transect WinScanopy software

12 Field data : LAI, FCover, FAPAR (grass) Derivation of LAI/FCover and LAI/FAPAR relationships at quadrat, ESU and km scale Evaluation of Can-Eye derived LAI (destructive measurements) and FAPAR (SunScan)

13 Seasonal variation of LAI (grass) Monitoring of 8 sites every 10 days during the rainy season

14 FORMOSAT-2 data (2007) Period: June -November Number: 29 images View angle: 53° Size: 58 x 24 km AOT images No SPOT data during the rainy season in 2007! (15 images in 2006) Landsat Aerial photos SPOT

15 Agoufou pond fire Bare sand dune Clay-silt plain Rocky outcrops (2007_06_09) Dry season AOT image Bare sand dune Agoufou

16 2007_08_04 Wet season AOT image - Begining of herbaceous vegetation growth - High spatial variability Agoufou

17 2007_08_24 Wet season AOT image Maximum of herbaceous vegetation LAI

18 08_20 08_12 29 images 24 with clear sky among which 15 were acquired during the rainy season : June : 4 July : 4 August : 5 September 6 DoY Example of atmospheric contamination

19 What do you mean by aerosols?

20 Land Cover

21 July 27 Temporary ponds Millet fields Road Field with high organic content Isolated Trees Acacia forest Formosat view of an agro-pastoral area (wet season) Sand dune covered by a grass layer Bare loamy soils

22 Comparison of HR images September, 2007 Formosat (8m)Landsat (30m)SPOT-5 (10m) FORMOSAT offer a better discrimination of cultivated areas

23 June 1July 27 September 29November 04 Time series of Formosat images over an agro-pastoral area Dry seasonWet season Dry season A large contrast between fields and grasslands during the rainy season (phenological differences) Burnt area

24 Land cover classification (work in progress) Hiernaux, Auda,… July 27 September 29 NDVI NIR Green Red 6 identified classes: LF, LJ, LN SF, SJ, SN J: fallow F: manured fields N: non manured fields L: loamy – sands S: Sand dune Only multi-date images enable LC to be discriminated

25 Vegetation monitoring and LAI mapping

26 Period of water stress well detected on NDVI images as well as regrowth of green vegetation Effect of straw/litter on NDVI NDVI seasonal variation over the Agoufou site JuneJulyAugustSept.

27 Lacombe, 2008; Larouziere, 2009 NDVI – LAI relationships : r² = 0.83 n = 115 VALERI methodology ESU scale : 10m x 10m

28 NDVI – LAI relationships (Field)° 2009_08_03 Le Dantec, 2009

29 August 4August 8August 20 Demarez, Mougin, in preparation Spatialization of LAI

30 Spatialization of LAI / Comparison with MODIS product 2 approaches are compared

31 Comparison with MODIS LAI Products All MODIS data Principal algorithm N = 29 N = 14 R² = 0.82R² = 0.94 Mougin, Demarez, in preparation

32 (Gardelle et al., in revision) Monitoring of Sahelian ponds : Ex of the Agoufou pond

33 Comparison FORMOSAT/MODIS/SPOT MODIS-2007SPOT-2005/06 Evaluation of a MODIS based methodology for surface water mapping

34 Concluding remarks High spatial and temporal resolution of Formosat data are found useful for : - Land cover mapping (change) of cultivated surfaces (small size) - Vegetation monitoring : detection of period of water stress - Mapping and monitoring of small ponds However, over sahel, data acquisition are hampered by aerosol and cloud contamination. As a consequence, no data was acquired during 2 weeks within the core of the growing season


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