Flood monitoring from remote sensing multi-sensor data analysis

J-F. Crétaux, M. Leblanc, S. Tweed,S. Calmant, R. Abarca Del Rio,G. Ramillien, & A. Cazenave

Geneva, November 2007

Monash University

Objectives: Mapping water extent variation

On high temporal resolutionMedium spatial resolution

Estimating water volume variation

Targets:Floodplain and highly variable lakes

In arid zones

Instruments:Modis sensor

Radar altimetry

Framework of the methodology

3 case studies

Steppes of Central AsiaAltiplano lakes & salars

Physic of the optical remote sensing measurements

What do we measure ?

MODIS

Band 1 (620 – 670 nm)Band 2 (841 – 876 nm)Band 3 (459 – 479 nm)Band 4 (545 – 565 nm)

Band 5 (1230 – 1250 nm)Band 6 (1628 – 1652 nm)Band 7 (2107 – 2155 nm)

Surface classification from Combination of band

Usual simple classification 1/2

From modis: B2<1000 or NDVI=(B2-B1)/(B2+B1) < 0 open waterNDVI>0.3/0.4 vegetation0<NDVI<0.3/0.4 dry land

Not true for:shallow water bodiesflood event (with suspended sediments)presence of aquatic vegetation

Usual simple classification 2/2

From radar altimetry:σ0 > 20 db open water

Only valid along altimeter profile=> no water extentNot true on dry salt lake

Backscatter with Topex on Lake Eyre

30

32

34

36

38

40

42

44

46

2002,5 2003 2003,5 2004 2004,5 2005 2005,5 2006

Backscatter envisat for lake Eyre

25272931333537394143

2002,5 2003 2003,5 2004 2004,5 2005 2005,5 2006

Lake cover by salt crust Lake filled by water

Case of shallow waterand floodplain

0

500

1000

1500

2000

2500

3000

3500

4000

4500

-27 -26,9 -26,8 -26,7 -26,6 -26,5 -26,4

Latitude (deg)

norm

aliz

ed re

flect

ance

Modis: Band 5

Modis: Band 2

-500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

44,4 44,6 44,8 45 45,2 45,4 45,6

latitude(deg)

norm

alis

ed re

flect

ance

Modis Band 5

Modis Band 2

Profile over Aral Sea Profile over Diamantina river

What happened if aquatic vegetation ?

NDVI & Band 5 surface reflectance are increasing

0

1000

2000

3000

4000

5000

6000

-26,95 -26,9 -26,85 -26,8 -26,75 -26,7 -26,65 -26,6 -26,55 -26,5 -26,45

Modis band 5

-0,3

-0,2

-0,1

0

0,1

0,2

0,3

0,4

-26,95 -26,9 -26,85 -26,8 -26,75 -26,7 -26,65 -26,6 -26,55 -26,5 -26,45

Modis NDVI

Open water Aquatic vegetation Vegetation Dry land

Classification of surface: threshold criterium

Open water if:Modis Band 5 < 1200

Aquatic vegetation if:1200<Modis Band 5 <2700 &NDVI < 0.4

Vegetation ifNDVI > 0.4

Dry land ifModis band 5 > 2700 &NDVI < 0.4

Lake Eyre and Diamantina river

March 9, 2003 March 16, 2003

Sequence of flood on Diamantina in 2003

March 30, 2003 April 30, 2003

Water: Black, Aquatic Veg: Red, Veg: Orange, Land: White

T/P crossover point on Goyder Lagoon

20

20,5

21

21,5

22

22,5

23

23,5

2003,2 2003,4 2003,6 2003,8 2004 2004,2 2004,4 2004,6 2004,8Date (year)

Hei

ght a

bove

geo

id (m

)

Surface and volume variation from Altimetry+Modis data

Goyder Lagoon, 2004's flood

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2003,9 2004 2004,1 2004,2 2004,3 2004,4 2004,5 2004,6 2004,7 2004,8 2004,9 2005

Date (year)

Surface (km

2 ) - Free Water

Acquatic Vegetation

Vegetation on dry land

Goyder Lagoon, 2004's Flood

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

2003,9 2004 2004,1 2004,2 2004,3 2004,4 2004,5 2004,6 2004,7 2004,8 2004,9 2005

Date (year)

Volume (km

3 ) -

Flooding sequence onLake EyreTopex / poseidon

-14,4-14,35-14,3

-14,25-14,2

-14,15-14,1

-14,05-14

-13,95

2004 2004,2 2004,4 2004,6 2004,8 2005

Date (Year)

Hei

ght a

bove

geo

id (m

)

From Modis surface reflectance

Topex / Poseidon

-14,4-14,35-14,3

-14,25-14,2

-14,15-14,1

-14,05-14

-13,95

2004 2004,2 2004,4 2004,6 2004,8 2005

Date (Year)

Hei

ght a

bove

Geo

id (m

)

Topex / Poseidon

-14,3-14,25-14,2

-14,15-14,1

-14,05-14

-13,95-13,9

2004,3 2004,4 2004,5 2004,6 2004,7 2004,8 2004,9 2005

Date (year)

Hei

ght a

bove

Geo

id (m

)

Validation of the method with Aral Sea

From altimetry + bathymetry = > variation of surfaceNorth Aral

39,5

40

40,5

41

41,5

42

42,5

43

43,5

1993 1995 1997 1999 2001 2003 2005 2007

Date (year)

Leve

l (m

Dam Dam

Dam Release

58.00 58.50 59.00 59.50 60.00 60.50 61.00 61.50 62.0043.00

43.50

44.00

44.50

45.00

45.50

46.00

46.50

47.00

0

5

10

15

20

25

30

35

40

45

50

55

60

65

Surface deduced from Altimetry+bathymetry

2200

2400

2600

2800

3000

3200

3400

3600

3800

1992 1994 1996 1998 2000 2002 2004 2006 2008

date (year)

surf

ace(

km 2 )

-

Direct measurement from analysis of the Modis images

Sept 5, 2004

Oct 10, 2005 Sept 14, 2007Sept 5, 2004

Modis / altimetry Aral surface variations

0

5000

10000

15000

20000

0 5000 10000 15000 20000Modis surface (km2)

Alti

met

ry s

urfa

ce (k

m2)

Small Aral Big Aral

Correlation modis/altimetry = 0.996

White:New underwaterSurface : 400 km2

Poopo and Salars (Coipasa/ Uyuni), Bolivia

Jan 28 Mar 03

Apr 19 Aug 29

Jan 09

Jan 29

May 25

2006

2004

2004Jan 28

Apr 19

Mar 03

Coipasa

0

500

1000

1500

2000

2500

3000

3500

2001 2002 2003 2004 2005 2006 2007 2008

Surfac

e of w

ater

(km2)

Uyuni

0

2000

4000

6000

8000

10000

12000

14000

2001 2002 2003 2004 2005 2006 2007 2008

Date(year)

Surface of water (k

m2)

Lake Poopo

0

500

1000

1500

2000

2500

3000

3500

4000

2001 2002 2003 2004 2005 2006 2007 2008Date (year)

surface (km2)

ConclusionConclusion

♦♦♦♦♦♦Modis data provide good mean to measure extent of water Modis data provide good mean to measure extent of water with high temporal resolution well designed for specific cases:with high temporal resolution well designed for specific cases:

shallow lakes, temporary lakes, & floodplains mainly in shallow lakes, temporary lakes, & floodplains mainly in arid zonearid zone

♦♦♦♦♦♦It provides valuable information on vegetation and aquatic It provides valuable information on vegetation and aquatic vegetationvegetation’’s dynamics dynamic♦♦♦It is not suitable in region covered by clouds most of the It is not suitable in region covered by clouds most of the timetime

=>=>Monitoring of floodplain extent and volume variation of Monitoring of floodplain extent and volume variation of lakes in synergy with radar altimetry is possiblelakes in synergy with radar altimetry is possible