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The sensors studied SeaWiFSMODIS-Aqua Launch date August 1 st, 1997 May 4, 2002 Equator crossing 12h13h30 Spectral coverage (nm) 402 – 885 (8 bands) 405.

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Presentation on theme: "The sensors studied SeaWiFSMODIS-Aqua Launch date August 1 st, 1997 May 4, 2002 Equator crossing 12h13h30 Spectral coverage (nm) 402 – 885 (8 bands) 405."— Presentation transcript:

1 The sensors studied SeaWiFSMODIS-Aqua Launch date August 1 st, 1997 May 4, 2002 Equator crossing 12h13h30 Spectral coverage (nm) 402 – 885 (8 bands) 405 – (36 bands) Data available since… 04/09/1997 (Level 3) (OC4v4 R51) 29/11/2002 (Level 3) (OC3M R11) Original spatial resolution 1100 m 1000 m Level-3 data put on a regular grid 1/12°x1/12°1/24°x1/24° Globcolour 1st User Consultation Meeting, Villefranche sur Mer, December 4-6, 2006 Merging of ocean color data from multiple satellite missions Merging of ocean color data from multiple satellite missions C. Pottier 1,2, V. Garçon 1, A. Turiel 3, G. Larnicol 2, J. Sudre 1, P.Y. Le Traon 4, P. Schaeffer 2 1 : LEGOS – 2 : CLS – 3 : ICM – 4 : IFREMER

2 Methods and zone of interest Error weighted- averagingError weighted- averaging Objective analysisObjective analysis  Global application for 2003 Wavelets (ongoing work)Wavelets (ongoing work) => Gulf Stream area –Globcolour 1st User Consultation Meeting – Methods and zone of interest – –Globcolour 1st User Consultation Meeting – Methods and zone of interest – Biogeochemical provinces [Longhurst, 1998]

3 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, R0, and 0304-R1 ARGAU3 DIAPAZON 7, 8, and 9 DYFAMED Other cruises (Yves Dandonneau, pers. com.)

4 SeaWiFS’ error measurementMODIS/Aqua’s error measurement % of chlorophyll

5 SeaWiFS’ biasMODIS/Aqua’s bias % of chlorophyll

6 Error-weighted averaging Objective analysis in Pottier et al., IEEE TGRS, 2006

7 Error-weighted averaging [Pottier et al., IEEE TGRS, 2006] [Gregg et al., IOCCG Report, 2006] Input parameters for each sensor:Input parameters for each sensor: –Map of chlorophyll for the i th day –Map of spatial errors (according to matchups) Computation made on logtransformed valuesComputation made on logtransformed values Output products:Output products: –Map of combined chlorophyll for the i th day –Map of associated errors – Globcolour 1st User Consultation Meeting Error-weighted-averaging – – Globcolour 1st User Consultation Meeting - Error-weighted-averaging –

8 Combined data Error Chlorophyll-a concentration (mg/m^3) 03/26/2003 % of chlorophyll SeaWiFS MODIS/Aqua Spatial repartition of the data

9 Objective analysis [Pottier et al., IEEE TGRS, 2006] [Gregg et al., IOCCG Report, 2006] Aim: to determine the value of a field  at a point in space and time, given various measurements of the field unevenly spread over time and space  obs i (i=1…n)Aim: to determine the value of a field  at a point in space and time, given various measurements of the field unevenly spread over time and space  obs i (i=1…n) Best least squares linear estimator  est (x) (Bretherton et al., 1976):Best least squares linear estimator  est (x) (Bretherton et al., 1976): A priori knowledge of:A priori knowledge of: –The covariance function (i.e. variance + correlation function) –The measurement noise and the bias (obtained from the matchups) – Globcolour 1st User Consultation Meeting – Objective analysis – – Globcolour 1st User Consultation Meeting – Objective analysis –

10 SeaWiFS MODIS/Aqua Spatial repartition of the data Combined data Error Chlorophyll-a concentration (mg/m^3) % of chlorophyll 03/26/2003

11 Wavelets Use of multi-resolution algorithm to compute 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

12 Wavelets [Pottier, Turiel and Garçon] 1st step: estimation of the missing data – Globcolour 1st User Consultation Meeting – Wavelets – Vertical details

13 Wavelets [Pottier, Turiel and Garçon] 2nd step: combination – Globcolour 1st User Consultation Meeting – Wavelets –

14 Weighted averaging (1/12°) MODIS/Aqua Original image (1/24°) Reconstructed image SeaWiFS Original image (1/12°) Reconstructed image Objective analysis (1/12°)Wavelets (1/24°) 03/26/2003

15 Ongoing work Weighted averaging and objective analysisWeighted averaging and objective analysis –Fully operational for near real time at the global scale –Statistics computation needed for all time series –Addition of other sensors (MERIS…) Wavelets: very promising ! But still a lot of work to do !Wavelets: very promising ! But still a lot of work to do ! – Globcolour 1st User Consultation Meeting Ongoing work – – Globcolour 1st User Consultation Meeting - Ongoing work –

16 Oceanographic application: using combined SeaWiFS and MODIS/Aqua ocean color data Southern ocean (35°S – 50°S)Southern ocean (35°S – 50°S) What are the dominant modes of variability in sea level anomalies and surface chlorophyll concentrations in this circumpolar belt ?What are the dominant modes of variability in sea level anomalies and surface chlorophyll concentrations in this circumpolar belt ? (Pottier et al., 2004; Pottier et al., 2006)

17 Band 45°S-50°S Weekly sea level anomalies Band 35°S-45°S Weekly combined chlorophyll SeaWiFS + MODIS/Aqua Monthly SeaWiFS chlorophyll period : 3/0 mode of variability

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19 Multi-resolution wavelets algorithm

20 In conclusion : Within MERSEA,Within MERSEA, – Globcolour 1st User Consultation Meeting – In conclusion – – Globcolour 1st User Consultation Meeting – In conclusion –

21 Error – Globcolour 1st User Consultation Meeting – Wavelets –


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