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An Optically-Based Technique for Producing Merged Water-Leaving Radiances; Validation and Application for the Mediterranean Basin Motivation: Combining.

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Presentation on theme: "An Optically-Based Technique for Producing Merged Water-Leaving Radiances; Validation and Application for the Mediterranean Basin Motivation: Combining."— Presentation transcript:

1 An Optically-Based Technique for Producing Merged Water-Leaving Radiances; Validation and Application for the Mediterranean Basin Motivation: Combining the data records of L WN from independent platforms to create a single consistent time series with optimal coverage Pre-requisite: Inter-comparison of sensor-specific products (Djavidnia et al., MERSEA report, 2006) Principle of the Technique & Field Data Validation of Radiometric Products (L WN ) & Merger Validation Test with a 3 rd Sensor (MERIS) Benefits of Merging & Time Series for the Mediterranean Global Environment Monitoring Unit, E.C. - Joint Research Centre Frédéric Mélin, Giuseppe Zibordi

2 L WN, 1 (λ i1 ) L WN, 2 (λ i2 ) … MERGER L WN, m (λ) bio-optical model parameters selection a* ph, S, η arbitrary wavelength Chla b bp (550) a ds+dt (440) 1. model inversion 2. forward mode Schematic of the merger: A two-step procedure Principle of the Technique [1] - combination of all available spectral information - selection of output wavelengths - the merged product is a primary radiometric quantity Mélin & Zibordi, submitted IOCCG Report #6, Chap.4

3 Bio-optical model: (inversion by non-linear LM inversion technique) Back-scattering: Absorption: parameters of the model variables of the model Principle of the Technique [2] Mélin & Zibordi, submitted Sensitivity Analysis: Dependence of the merged outputs on the bio-optical parameter set: < 4% (tested for various combinations of η, S, a * ph )

4 CE-318 (sea-viewing)CE-318 (sky-viewing) Optical Field Measurements: Acqua Alta Oceanographic Tower AAOT Above-Water Radiometry AERONET-OC (May 2002) SeaPRISM L wn at 412, 440, 500, 555, 675 nm AERONET (Jul now) AERONET-OC Zibordi et al., EOS, 2006 Mélin et al., IEEE, 2003 Zibordi et al., IJRS, 2004 Mélin & Zibordi, GRL, 2005 Mélin et al., JGR, 2006 Mélin et al., RSE, accepted Operational validation of OC radiometric products [ SeaWiFS, MODIS-T, -A, MERIS, GLI ] Zibordi et al., IEEE, 2004, 2006 Zibordi et al., GRL 2006, EOS 2006, ECSS 2006

5 SeaPRISM SeaWiFS Validation of SeaWiFS Radiometric Products Zibordi, Mélin, Berthon, GRL, 2006 SeaWiFS vs. SeaPRISM match-ups

6 Validation of MODIS Radiometric Products MODIS-A Zibordi, Mélin, Berthon, GRL, of these SeaWiFS and MODIS match-ups are on the same day, and can be the basis for validating the merged product significant match-up dataset for both sensors MODIS vs. SeaPRISM match-ups SeaPRISM

7 Merger Validation SeaPRISM MERGED SeaWiFS only SeaWiFS + MODIS (N=173) MODIS only MERGED vs. SeaPRISM match-ups Mélin & Zibordi, submitted

8 SeaPRISM MERIS Overestimate of L WN in the blue SeaWiFS & MODIS Test with 3 rd Sensor: MERIS [1] Mélin & Zibordi, submitted

9 SeaPRISM MERGED MERIS+MODIS+SeaWiFS Test with 3 rd Sensor: MERIS [2] NB: Compensation of Overestimate and Underestimate of L WN in the blue

10 Benefits of Merging [1] Time Series at AAOT site SeaWiFS only (110) SeaWiFS + MODIS (213) MODIS only (150) N=473 over ~ 4 years SeaWiFS (363) MODIS (323) Mélin & Zibordi, submitted

11 MODIS nm SeaWiFS nm MODIS nm SeaWiFS nm MERGED nm MERGED nm Daily spatial coverage - 19 th Jul Benefits of Merging [2]

12 Benefits of Merging [3] SeaWiFS MODIS Merged 36% Daily coverage over the Mediterranean Sea for 2003 (2-km gridded products) 22% 42% Mélin, Zibordi, Djavidnia, submitted Nb. Days – 2003

13 Time Series of Differences Mélin, Zibordi, Djavidnia, submitted 2|SWF-MOD|/(SWF+MOD) 2(SWF-MOD)/(SWF+MOD) RMSD(SWF-MOD)

14 The Merged Series Mélin, Zibordi, Djavidnia, submitted

15 CONCLUSIONS Presentation and validation of a merging technique for the production of a L WN multi-sensor record Performance at least as good as for the sensor-specific products Merges in a consistent way the various sensor-specific L WN spectra, taking full advantage of the available spectral bands Allows the subsequent applications of any bio-optical algorithm Application on the Mediterranean Sea with time series of differences and merged products Still a lot to learn from the inter-comparison of the sensor-specific products


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