ISAC Contribution to Ocean Color activity Mediterranean high resolution surface chlorophyll mapping Use available bio-optical data sets to estimate the uncertainties of the existing ocean colour algorithms and to define an optimal chlorophyll algorithm for the Mediterranean Sea (case I water). Adapt the OC processing software to include selected regional algorithms and validate satellite chlorophyll estimates on the basis of in situ data. Evaluate the uncertainties of all current global satellite chlorophyll products available from public archive (e.g. DAAC) in the Mediterranean Contribute to reprocessing SeaWiFS dataset using the selected Mediterranean algorithm Prepare Mediterranean gridded data compatible with model requirements.

ISAC Contribution to Ocean Color activity Comparison of different ocean colour sensors and development of inter-calibration and merging techniques Contribute to the definition of the suitable intercaliblation and merging tecnique for OC data Identificatify the characteristic time/space scales of the chlorophyll field in the Mediterranean Sea Develop an appropriate method to produce daily fields of ocean colour parameters for data assimilation for Mediterranean Sea. Define an optimal interpolation algorithm that takes in to account the different characteristics of ocean colour retrieval in case I/case II waters. Validate SeaWiFS, Polder, MODIS, MERIS chlorophyll products as well as merged binned data produced by Mersea ageist in situ observation

Why Mediterranean needs regional algorithm ? Chlorophyll concentrations over the oligotrophic waters of the Mediterranean Sea are systematically overestimated when global algorithms (e.g. OC4v4) are used to convert blue-to-green reflectance ratios in to chlorophyll-a concentrations: Gitelson et al. (Journal of Marine System, 1996) D’Ortenzio et al. (SIMBIOS meeting January 2001) D’Ortenzio et al. (Remote sensing of the Environment, 2002) Bricaud et al. (Remote sensing of the Environment, 2002) Claustre et al. (Geoph. Res. Letters, 2002) From these works it results that global algorithms cannot be applied to-court to the Mediterranean Sea but a specific cal/val activity is needed.

Validation of Chlorophyll estimated by SeaWiFS against in situ Chlorophyll and bio-optical measurements in situ bio-optical measurements and concurrent in situ chlorophyll-a data Satellite geophysical parameter retrieval and validation SeaWiFS chlorophyll-a estimates validation against concurrent in situ chlorophyll-a From D’Ortenzio et al., Rem. Sens. Env, 2002 A regional algorithm is required

Validation of Chlorophyll estimated by SeaWiFS against in situ Chlorophyll measurements: Crosses; SATLANTIC band- ratio vs. in situ chlorophyll. Dashed line: NASA OC4V4 algorithm Continuous lines: L-DORMA and NL-DORMA. Satellite geophysical parameter retrieval and validation Scatter plot NL-DORMA versus concurrent in situ chlorophyll-a data From D’Ortenzio et al., Rem. Sens. Env, 2002

Applicazione del DORMA alle immagini di clorofilla

Validation of SeaWiFS ocean color algorithms in the Mediterranean Sea ENEA -CR Casaccia – Sezione Modellistica Oceanografica Stazione Zoolologica ‘A. Dohrn’ Laboratorio di Oceanografia Biologica 3 2 1

Validation of empirical SeaWiFS algorithms for chlorophyll-a retrieval in the Mediterranean Sea: a case study for oligotrophic seas By Fabrizio D’Ortenzio, Salvatore Marullo, Maria Ragni, Maurizio Ribera d’Alcalà, Rosalia Santoleri Remote Sensing of the Environment, 2002 DORMA Algorithm based on data New data from 2000 to 2003: an independent data-set Validation of DORMA, Bricout and MERIS algorithms for the Mediterranean Sea

Bio-optical measurements: (103 chl/opt measurement points) to define the Mediterranean regional algorithm In water downwelling irradiance and upwelling radiance profiles using SATLANTIC SPMR above water measurements using the SIMBAD and SIMBADA radiometer In the bio-optical stations phytoplankton pigments distribution (HPLC and spectro-fluorometric analysis) and ancillary biological data were also acquired following NASA protocols. In situ chlorophyll-a data: (> 800 chl profiles) to validate SeaWiFS, Polder, MODIS, MERIS chlorophyll products and merged level 3 binned data produced by Mersea Mediterranean Ocean Color CAL/VAL DATA SETS 10 Mediterranean cruises from 1998 up to now where made in framework of Italian National Projects

Why the oligotrophic Mediterranean waters are greener? Two possible answers

A1. The role of the Sahara dust Claustre et al suggest that, the oligotrophic waters of the Mediterranean Sea are greener than would result from their phytoplankton content alone because of the presence of Saharan dust in the upper layer that enhance absorption in the blue and backscattering in the green.

Variations in the Rrs(490)/Rrs(555) band ratio with chlorophyll-a concentration. Squares represent the in situ bio-optical measurements and the concurrent chlorophyll-a. The solid line is the semi-analytic radiance model presented in section 4. The CaCO 3 concentration for the four lines are 0,1,5,50 mg/m 3. The thick line represents the lower CaCO 3 concentration. The higher CaCO 3 concentrations yield the “flatter” curves.(D’Ortenzio et al. 2002) A2. The role of Coccolithophores CaCO 3 concentration of 5 mg/m 3. This amount of calcite would in fact correspond to a coccolithophore concentration in the range between of 3·10 4 ÷2.5·10 5 cells/dm 3