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ISAC Contribution to Ocean Color activity

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 (chlorophyll and PP)

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ISAC Contribution to Ocean Color activity

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  1. 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 (chlorophyll and PP) • Use bio-optical data 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.

  2. 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

  3. Outline • Introduction • Data and methods • Validation of OC algorithms: Regional vs Global • Adaptation of the global scale PP algorithm for the Mediterranean Sea • Conclusions

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

  5. Introduction • 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.

  6. 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 1998-2000 data New data from 2000 to 2003: an independent data-set Validation of DORMA and MERIS algorithms for the Mediterranean Sea

  7. Validation of Chlorophyll estimated by SeaWiFS against in situ Chlorophyll and bio-optical measurements Satellite geophysical parameter retrieval and validation in situ bio-optical measurements and concurrent in situ chlorophyll-a data 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

  8. Ocean Color Cal/Val Activity: Bio-optical measurements: 10 Mediterranean cruises (in the framework of ASI Projects and ESA AO) from 1998 up to now. (103 chl/opt measurement points) Satellite geophysical parameter retrieval and validation • In water downwelling irradiance (Ed) and upwelling radiance (Lu) profiles using SATLANTIC SPMR radiometer (400, 412, 443, 470, 490, 510, 532, 555, 590, 620, 665, 683, 700 nm) • above water measurements using the SIMBAD radiometer operating at 443nm, 490nm, 565nm, 670nm and 870nm. nm and SIMBADA radiometer operating at 350nm, 380nm, 412nm, 443nm, 490nm, 510nm, 565nm, 620nm, 670nm, 750nm and 870 nm • In the bio-optical stations phytoplankton lipophilic pigments distribution (HPLC and spectrofluorometric analysis) and ancillary biological data were also acquired following NASA protocols (M. Ribera Stazione Zoologica Napoli).

  9. SIMBAD,SIMBADA, SATLANTC, SeaWiFS and MERIS channels central wavelengths between 400 and 700 nm

  10. In situ chlorophyll-a profiles and optical measurements (103 stations) were performed during several cruises carried out in the Mediterranean Sea through the years 1998-2003 on board the R/V Urania of the National Research Council (CNR). SIMBIOS data taken during PROSOPE cruise were also included Satellite geophysical parameter retrieval and validation

  11. Four Ocean Color Algorithms MERIS ATBD 2.9 : R is log10 of either the 443/560 or the 490/560 or the 510/560 band reflectance ratios. The switch from one band ratio to another one is based on the chlorophyll concentration itself. Coefficients changes according to the selected ratio. OC4v4:R is log10 of either the 443/555 or the 490/555 or the 510/555 band reflectance ratios, depending on its value (the maximum is chosen) D’Ortenzio et al. 2002 (DORMA):R is log10 of the 490/555 band reflectance ratios. Bricaud et al. 2002: R is log10 of the 443/555 band reflectance ratios for low chl (OC4v4 is used in the other cases)

  12. ERROR TABLE

  13. Primary production in the Mediterranean Sea from remote sensing data: a model adaptation

  14. Depth (m) Depth (m) CHL (mg m-3) CHL (mg m-3)

  15. Remote Sensed data of pigment concentration Trophic States e Morel and Berthon’s (1989) Correlations Primary Production Maps

  16. WEST MED: 197 gc m-2 y-1 Antoine et al.,1995 EST MED: 137 gc m-2 y-1 WEST MED: 172 gc m-2 y-1 Bosc et al.,2003 WEST MED: 78-150 gc m-2 y-1 EST MED: 123 gc m-2 y-1 In situ C14 Method EST MED: 55-97 gc m-2 y-1

  17. Chlorophyll concentration intervals: >0.05, 0.05-0.1, 0.1-0.15, 0.15-0.3, 0.3-0.45, 0.45-1.5, 1.5-5, > 5 mg m-3 4000 chlorophyll profiles acquired in the Mediterranean Sea during 16 cruises (1996-up to now) has been use to compute the chlorophyll concetration of the of the first optical depth (Cpd)

  18. Chlorophyll vertical distribution in first two trophic states Morel (dashed line) This work (continuous line)

  19. Morel (dashed line) This work (continuous line)

  20. = Ctot=40.6 Cpd0.46 Ctot=40.6 Csat0.459 ≠ Ctot=54.679 Cpd0.6532 Ctot=48.13 Csat0.627

  21. Gennaio Febbraio Marzo Aprile Maggio Giugno Luglio Agosto Settembre Ottobre Novembre Dicembre 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 gc m-2 g-1

  22. WEST MED: 197 gc m-2 y-1 Antoine et al.,1995 EST MED: 137 gc m-2 y-1 WEST MED: 172 gc m-2 y-1 Bosc et al.,2003 EST MED: 123 gc m-2 y-1 WEST MED: 130 gc m-2 y-1 Our Estimate WEST MED: 78-150 gc m-2 y-1 EST MED: 95 gc m-2 y-1 In situ C14 method EST MED: 55-97 gc m-2 y-1

  23. Conclusions • The analysis of bio-optical measurements revealed a systematic overestimation of chlorophyll-a concentration by global algorithms. The error appears to be correlated with chlorophyll-a concentration, by exhibiting marked differences at low values (C < 0.1 mg/m3). At low concentration, the mean observed bias is close to 100% for OC4v4. • A better performance is observed when regional algorithms are applyed • The OC algorithm proposed for MERIS still needs to be refined for the Mediterranean case. • DORMA algorithm, validated using the new independent data set, performs well over the all measured chl range (0.02 -2.70 mg/m3) • A new database with all bio-optical data is in preparation, and will be use to define a new advanced Mediterranean regional algorithm • The preparation of new data base of in situ chlorophyll measurements is on going and will be used to construct mach-up data files for validation of satellite product

  24. Conclusions • The development of the adaptation of the Morel PP model to the Mediterranean bio-optical conditions is underway • The bio-optical data acquired in the last 5 years has been used to adapt the parameter entering in Morel PP model to the Mediterranean conditions • New trophic states has been defined in the Mediterranean Sea on basis of the in situ chlorophyll profiles • A first tentative to use these new parameterizations in the PP model results into PP estimates more near to in situ observations. The development of the adaptation of the Morel PP model to the Mediterranean bio-optical conditions is underway

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