The sensors studiedThe sensors studiedSeaWiFSSeaWiFS MODIS-MODIS-

AquaAqua

Launch dateLaunch date August 1August 1stst, , 19971997

May 4, May 4, 20022002

Equator crossingEquator crossing 12h12h 13h3013h30

Spectral coverage (nm)Spectral coverage (nm) 402 – 885402 – 885

(8 bands)(8 bands)405 – 405 – 1438514385

(36 bands)(36 bands)

Data available since…Data available since… 04/09/199704/09/1997

(Level 3)(Level 3)

(OC4v4 R51)(OC4v4 R51)

29/11/200229/11/2002

(Level 3)(Level 3)

(OC3M (OC3M R11)R11)

Original spatial resolutionOriginal spatial resolution 1100 m1100 m 1000 m1000 m

Level-3 data put on a regular Level-3 data put on a regular gridgrid

1/12°x1/12°1/12°x1/12° 1/24°x1/24°1/24°x1/24°

Globcolour 1st User Globcolour 1st User Consultation Meeting, Consultation Meeting, Villefranche sur Mer, Villefranche sur Mer, December 4-6, 2006December 4-6, 2006

Merging of ocean color dataMerging of ocean color datafrom multiple satellite missionsfrom multiple satellite missions

C. Pottier1,2, V. Garçon1, A. Turiel3, G. Larnicol2, J. Sudre1, P.Y. Le Traon4 , P. Schaeffer2

1 : LEGOS – 2 : CLS – 3 : ICM – 4 : IFREMER

Methods and zone of Methods and zone of interestinterest

• Error weighted-Error weighted-averagingaveraging

• Objective analysisObjective analysis Global application Global application

for 2003for 2003

• Wavelets (ongoing Wavelets (ongoing work)work)

=> Gulf Stream area=> Gulf Stream area

– –Globcolour Globcolour 1st User Consultation Meeting 1st User Consultation Meeting – – Methods and zone of interest – Methods and zone of interest –

11

1

22 3

4

56

7

89

10

11

12

1314

15

16

17

1819

20

21

22

30

3132

33 34 3536

37

50 5050

51 52

53 5454

56

58

59

60

61

6263

64

65

66

67

68

64

69

70

71

72

80 8080

81 81

8282

8383 83

Biogeochemical provinces

[Longhurst, 1998]

SeaWiFS: 2410 matchups

MODIS/Aqua: 2789 matchups

YEAR 2003

•AMT 12 and AMT 13 (Atlantic Meridional Transect, UK) •SeaBASS (SeaWiFS Bio-optical And Storage System, USA)•National Oceanographic Data Center (USA)•International Council for the Exploitation of the Sea•National Institute of Oceanography (India)•OISO•MINERVE 0203-R2, 0204-R4, 0304-R0, and 0304-R1•ARGAU3•DIAPAZON 7, 8, and 9•DYFAMED•Other cruises (Yves Dandonneau, pers. com.)

SeaWiFS’ error measurement MODIS/Aqua’s error measurement

% of chlorophyll % of chlorophyll

valuesituin:I

valuesatellite:S

matchupsofnumber:N

110

110RMS

IlogSlogN

1RMS

N

1n

2n10n10

log

IlogSlogN1

RMS%d

N

1n

2n10n10log

SeaWiFS’ bias MODIS/Aqua’s bias

% of chlorophyll % of chlorophyll

valuesituin:I

valuesatellite:S

matchupsofnumber:N

110

110BIAS

IlogSlogN

1BIAS

N

1nn10n10

log

IlogSlogN1

BIAS%d

N

1nn10n10log

Error-weighted averagingObjective analysis

in

Pottier et al., IEEE TGRS, 2006

Error-weighted averagingError-weighted averaging[Pottier [Pottier et al.et al., IEEE TGRS, 2006], IEEE TGRS, 2006][Gregg [Gregg et al.et al., IOCCG Report, 2006], IOCCG Report, 2006]

• Input parameters for each sensor:Input parameters for each sensor:– Map of chlorophyll for the iMap of chlorophyll for the ithth day day– Map of spatial errors (according to Map of spatial errors (according to

matchups)matchups)

• Computation made on Computation made on logtransformed valueslogtransformed values

• Output products:Output products:– Map of combined chlorophyll for the iMap of combined chlorophyll for the ithth

dayday– Map of associated errors Map of associated errors

– – Globcolour 1st User Consultation MeetingGlobcolour 1st User Consultation Meeting - Error-weighted-averaging – Error-weighted-averaging –

Combined data

Error

Chlorophyll-a concentration (mg/m^3)

03/26/2003% of chlorophyll

SeaWiFS

MODIS/Aqua

Spatial repartition of the data

Objective analysisObjective analysis[Pottier [Pottier et al.et al., IEEE TGRS, 2006], IEEE TGRS, 2006][Gregg [Gregg et al.et al., IOCCG Report, 2006], IOCCG Report, 2006]

• Aim: to determine the value of a field Aim: to determine the value of a field at a point in space and at a point in space and time, given various measurements of the field unevenly spread time, given various measurements of the field unevenly spread over time and space over time and space obsobs

ii (i=1…n) (i=1…n)• Best least squares linear estimator Best least squares linear estimator estest(x) (Bretherton et al., (x) (Bretherton et al.,

1976):1976):

• A priori knowledge of:A priori knowledge of:– The covariance function (i.e. variance + correlation function)The covariance function (i.e. variance + correlation function)– The measurement noise and the bias (obtained from the The measurement noise and the bias (obtained from the

matchups)matchups)

– – Globcolour 1st User Consultation MeetingGlobcolour 1st User Consultation Meeting – Objective analysis –– Objective analysis –

N

i

N

jobsxjijest iCAx

1 1

1

N

i

N

jijxjxixx ACCCe

1 1

12

SeaWiFS

MODIS/Aqua

Spatial repartition of the data

Combined data

Error

Chlorophyll-a concentration (mg/m^3)

% of chlorophyll

03/26/2003

WaveletsWaveletsUse of multi-resolution algorithm to Use of multi-resolution algorithm to compute the wavelet coefficientscompute the wavelet coefficients

« h »: convolution with a low-pass filter« g »: convolution with a high-pass filter« 2 »: keep 1 row (or col.) on 2

Wavelets Wavelets [Pottier, Turiel and Garçon][Pottier, Turiel and Garçon]

1st step: estimation of the missing 1st step: estimation of the missing datadata

–– Globcolour 1st User Consultation MeetingGlobcolour 1st User Consultation Meeting – Wavelets – – Wavelets –

42242

32232

22222

12212

logPlogFlog

logPlogFlog

logPlogFlog

logPlogFlog

Vertical details

Wavelets Wavelets [Pottier, Turiel and Garçon][Pottier, Turiel and Garçon]

2nd step: combination2nd step: combination

–– Globcolour 1st User Consultation MeetingGlobcolour 1st User Consultation Meeting – Wavelets – – Wavelets –

Weighted averaging (1/12°)

MODIS/Aqua

Originalimage(1/24°)

Reconstructedimage

SeaWiFS

Originalimage(1/12°)

Reconstructedimage

Objective analysis (1/12°)Wavelets (1/24°)

03/26/2003

Ongoing workOngoing work

• Weighted averaging and objective Weighted averaging and objective analysisanalysis– Fully operational for near real time at the Fully operational for near real time at the

global scaleglobal scale– Statistics computation needed for all time Statistics computation needed for all time

seriesseries– Addition of other sensors (MERIS…)Addition of other sensors (MERIS…)

• Wavelets: very promising ! But still a Wavelets: very promising ! But still a lot of work to do !lot of work to do !

– – Globcolour 1st User Consultation MeetingGlobcolour 1st User Consultation Meeting - Ongoing work – Ongoing work –

Oceanographic application:Oceanographic application:using combined SeaWiFS and using combined SeaWiFS and MODIS/Aqua ocean color dataMODIS/Aqua ocean color data

• Southern ocean Southern ocean (35°S – 50°S)(35°S – 50°S)

• What are the What are the dominant modes of dominant modes of variability in sea variability in sea level anomalies and level anomalies and surface chlorophyll surface chlorophyll concentrations in concentrations in this circumpolar this circumpolar belt ?belt ?

(Pottier et al., 2004; Pottier et al., 2006)

Band 45°S-50°S

Weekly sea levelanomalies

Band 35°S-45°S

Weekly combined chlorophyllSeaWiFS + MODIS/Aqua

Monthly SeaWiFSchlorophyll

2002-2006 period : 3/0 mode of variability

Multi-resolution wavelets algorithm

In conclusion :In conclusion :

• Within MERSEA, Within MERSEA,

– – Globcolour 1st User Consultation MeetingGlobcolour 1st User Consultation Meeting – In conclusion – – In conclusion –

ErroErrorr

–– Globcolour 1st User Consultation MeetingGlobcolour 1st User Consultation Meeting – Wavelets – – Wavelets –