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 –