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 http://marine.jrc.ec.europa.eu 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. 1996 - 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, 2006 173 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 - 412 nm SeaWiFS - 412 nm MODIS - 551 nm SeaWiFS - 555 nm MERGED - 412 nm MERGED - 555 nm Daily spatial coverage - 19 th Jul. 2003 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