1. Development of ocean color algorithms in the Mediterranean Sea
Rosalia Santoleri1,, Gianluca Volpe 1, Simone Colella1,3, Salvatore Marullo2, Maurizio Ribera D’Alcalà3, Vincenzo Vellucci3 1 2
ENEA -CR Casaccia – Sezione Modellistica Oceanografica 3
Stazione Zoolologica ‘A. Dohrn’ Laboratorio di Oceanografia Biologica

2. 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.
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
Reprocessing SeaWiFS dataset using the selected Mediterranean algorithm
Prepare Mediterranean gridded data compatible with model requirements.

3. 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.

4. Mediterranean Ocean Color CAL/VAL DATA SETS
10 Mediterranean cruises from 1998 up to now were organized by ISAC in the framework of Italian National Projects
Bio-optical stations
Bio-optical measurements: (143 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: (872 chl profiles) to validate SeaWiFS, Polder, MODIS, MERIS chlorophyll products and merged level 3 binned data produced by Mersea

5. Cruise Period Zone # of profiles Chlorophyll Range Satlantic SIMBAD(A)
MIN
MAX
MATER 4
25/4/1998
15/5/1998
Sardinia Channel
Sicily Channel 57
0.025
0.105 -
MATER 5
20/10/1998
27/10/1998 50
0.047
0.085
EMTEC 99
20/4/1999
7/5/1999
Ionian Sea
125
0.039
0.137 20
MATER 6
14/5/1999
30/5/1999
100
0.003
0.135
PROSOPE
04/09/1999
14/10/1999
Western Basin 16
0.020
0.112
SYMPLEX 99
21/10/1999
6/11/1999
212
0.176 12
NORBAL 1
26/3/2000
19/4/2000
Gulf of Lions 81
0.113
2.289
NORBAL 2
5/12/2001
20/12/2001
Tyrrhenian Sea 65
0.088
0.386 13 14
NORBAL 4
6/3/2003
26/3/2003
115
0.428
7.061 28
NORBAL 5
18/4/2003
25/4/2003 40
0.605
2.096 4 7
DINA*
29/3/2001
28/8/2001
Gulf of Naples 11
0.079
0.455
DYFAMED*
5/2/1998
25/11/2002
Liguro-Provencal 55
0.042
2.366
All cruises
Mediterranean
872 92 49
141

6. In situ chlorophyll-a profiles and optical measurements (143 stations) were performed during several cruises carried out in the Mediterranean Sea through the years 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

7. Validation of Ocean Color Algorithms
REGIONAL
Validation of Ocean Color Algorithms
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 (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 Chl<0.2 (OC4v4 is used in the other cases)
GLOBAL

9. NEW MEDITERRANEAN ALGORITHM
MEDOC4 : R is log10 of either the 443/560 or the 490/555 or the 510/555 band reflectance ratios. The switch from one band ratio to another one is based on the chlorophyll concentration itself (the Maximum is Chosen)

12. SeaWiFS data validation
A Match-up dataset between concurrent SeaWiFS data and in situ measurements has been contructed
SeaWiFS L1A passes corresponding to in situ observation were selected
The regional algorithms (DORMA, Bricout et al, and the new MED OC4) were inserted in the SeaDAS Code
SeaWiFS L1A passes were processed using the different algorithms
A Match-up dataset is contructed.

13. Map of the Satellite-in situ match-up stations

16. Merging OC data in the MED
Define the error of global OC color products at regional scale and define a strategy to take into account the regional optical properties of the MED
Define of the suitable intercalibration and merging tecnique for OC
Define an optimal interpolation algorithm that takes in to account the different characteristics of ocean colour retrieval in case I/case II waters.

17. 10 March 2003

18. 12 March 2003

19. 25 March 2003

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

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

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

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

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

28. Chlorophyll concentration intervals:
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)
Chlorophyll concentration intervals:
>0.05, , , ,
, , 1.5-5, > 5 mg m-3

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

30. = ≠ Ctot=40.6 Cpd0.46 Ctot=40.6 Csat0.459 Ctot=54.679 Cpd0.6532

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

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