Ph

oto

: D

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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

• The study site

• FORMOSAT data

• Field data

• Applications

Content

The AMMA Gourma site

Anomalies of annual rainfall, Hombori, 1920-2009

-300

-200

-100

0

100

200

300

400

500

19

20

19

25

19

30

19

35

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45

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55

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60

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65

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75

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85

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95

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20

05

mean = 373 mm

Short rainy season : JJASHigh rainfall variabilityHigh 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

The Hombori site(15.3°N, 1.6°W)

AERONET photometer

Radiometer / PAR sensor

The Gourma land units

Shrub Savannah

Open forestFlooded plains

LAI : 2 - 4

LAI : 0.5 - 2

LAI : 2 - 4

The Gourma land units

PondErosion surface

Tiger bushMillet field

LAI : < 0.1

LAI : 0.5 - 2

Sand dunes

Open forest

Erosion surface

60 kmTiger bush

Ponds

SPOT-HRV image

Monitoring site

Agoufou

July 15

May 29June 06

July 17

2005

August 20August 19

A strong seasonal dynamics and a high inter annual variability of vegetation cover

2006 2007

July 16

June 08

August 23

July 05 August 26July 28

July 02 August 27 September 16

Seasonal dynamics of acacia forests and millet fields

Field data : LAI, FCover, FAPAR

Use of hemispherical photographs

Field data : LAI, FCover, FAPAR (trees)

Isolated trees

Open Acacia forest : 500 m transect

WinScanopysoftware

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)

Seasonal variation of LAI (grass)

Monitoring of 8 sites every 10 days during the rainy season

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

Agoufou pondfireBare sand dune

Clay-silt plain

Rocky outcrops

(2007_06_09)Dry season AOT image

Bare sand dune

Agoufou

2007_08_04

Wet season AOT image

- Begining of herbaceous vegetation growth

- High spatial variability

Agoufou

2007_08_24

Wet season AOT image

Maximum of herbaceous vegetation LAI

08_20

08_12

29 images

24 with clear sky among which 15 were acquired during the rainy season :

June : 4July : 4August : 5September 6

DoY

Example of atmospheric contamination

What do you mean by aerosols?

Land Cover

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

Comparison of HR images

September, 2007

Formosat (8m)Landsat (30m) SPOT-5 (10m)

FORMOSAT offer a better discrimination of cultivated areas

June 1 July 27 September 29 November 04

Time series of Formosat images over an agro-pastoral area

Dry season Wet season Wet season Dry season

A large contrast between fields and grasslands during the rainy season (phenological differences)

Burnt area

Land cover classification (work in progress)

Hiernaux, Auda,…

July 27

Sep

tem

ber

29

NDVI

NIR

Green

Red

6 identified classes:

LF, LJ, LN SF, SJ, SNJ: fallowF: manured fieldsN: non manured fields

L: loamy – sandsS: Sand dune

Only multi-date images enable LC to be discriminated

Vegetation monitoring and

LAI mapping

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

June July August Sept.

NDVI en fonction des LAI vrais

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0 1 2 3 4

LAI

ND

VI

Site17_3107

Site17_1508

Site18_0108

Site18_1608

Site19_0108

Site21b_0308

Site31_3107

Site31_1608

Site21b_1608

Site19_1608

Site17_2708

Série12

Site41_1708

site41_0208

sol nu

Lacombe, 2008; Larouziere, 2009

NDVI – LAI relationships :

r² = 0.83

n = 115

VALERI methodology

ESU scale : 10m x 10m

y = 1.4446x + 0.0788

R2 = 0.9207

y = 1.1309x + 0.0574

R2 = 0.9575

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

LAI

ND

VI

Photo H

planimètre

NDVI – LAI relationships (Field)°

2009_08_03

Le Dantec, 2009

August 4 August 8 August 20

Demarez, Mougin, in preparation

Spatialization of LAI

Spatialization of LAI / Comparison with MODIS product

2 approaches are compared

Comparison with MODIS LAI Products

200 400 600 800 1000 1200 14000

0.5

1

1.5

2

DAY of YEAR (Since 2005/01/01)

LA

I (m

2 m-2)

Site 17 (2005 - 2008)

2005 2006 2007 2008

MODIS LAILAI in situ

0 0.5 1 1.5 2 2.50

0.5

1

1.5

2

2.5

in situ LAI

MO

DIS

LA

I

0 0.5 1 1.5 2 2.50

0.5

1

1.5

2

2.5

in situ LAI

MO

DIS

LA

I

All MODIS data Principal algorithm

N = 29 N = 14

R² = 0.82 R² = 0.94

Mougin, Demarez, in preparation

(Gardelle et al., in revision)

Monitoring of Sahelian ponds : Ex of the Agoufou pond

Comparison FORMOSAT/MODIS/SPOT

MODIS-2007 SPOT-2005/06

Evaluation of a MODIS based methodology for surface water mapping

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