Illustration of POLDER-2 capabilities in term of global coverage

Rayleigh-corrected, true-color image of POLDER-2 daily coverage (2003, July 17th)

 

The corresponding daily chlorophyll concentration (2003, July 17th)

 

The level-3 monthly synthesis of chlorophyll concentration on July 2003

Marine parameters over the Mediterranean Sea and the Gulf of Mexico

Monthly mean values of the chlorophyll concentration Chl, the absorption coefficients a(443), and the backscattering coefficient b_bp(565) retrieved over the Mediterranean Sea and the Gulf of Mexico in April 2003. a and bb provide new additional biogeochemical information such as particulate load (through bbp), and the opportunity to distinguished different families of suspended marine particles. While a(443) shows relatively similar spatial patterns to the Chl ones, some clear differences appear in the bbp spatial distribution (some exemples into white circles, and squares). Large values in the Gt Bahama Bank are mostly due to bottom effect.

 

In-situ validation

Marine Reflectances

Validation has been carried on using SIMBADA (http://www-loa.univ-lille1.fr/simbadA/) in-situ measurements of above-water marine reflectances. Comparison is made for under-water reflectances after correction of the air-sea interface. Validation of the Aerosol Optical Thickness used for atmospheric correction is also included here.
From the 396 match-up between SIMBAD A et POLDER 2, 101 remained after elimination of possible cloud contamination, negative marine reflectances, bad quality measurements...

Differences between POLDER 2 derived and SIMBAD A in-situ measured marine reflectances below the surface as a function of time given by the POLDER 2 orbit number. There is no evidence of a trend that would be linked to a drift of the radiometric calibration.

 

Linear regression between POLDER 2 derived and SIMBAD A in-situ measured marine reflectances below the surface. About one hundre match up scenes have been retained for this analysis, and their location is given in the Figure above. The performances are given in the Table. A systematic bias of about 0.002 on the reflectances is observed at all wavelengths while the standard deviation is about 0.004. This value of 0.004 is a little above the mission requirements and is critical for an accurate estimate of the Chlorophyll concentration.

 
Chlorophyll-a concentrations and bio-optical parameters

Spatial repartition of in-situ measurements after filtering.

 

Comparison between POLDER2-derived Chl and in-situ measured Chl (by HPLC method), with OC2-v4 like algorithm (in red), and the new algorithm (in blue).

 

Comparison of the POLDER2-derived and the measured absorption coefficients at 490 and 443 nm. The absorption coefficient represents the absorption by particles and dissolved material.

 

Comparison of POLDER2-derived and the measured particulate backscattering coefficient.

Acknowledgements: Many thanks to Y. Dandonneau (LODYC, skogafoss and guyplac cruises), R. Frouin (Scripps, GLI data set), D. Antoine (LOV, BOUSSOLE project), J. Rass (LOV), S. Maritorena (UCSB), J-F. Berthon (JRC), J. Zibordi (JRC), and people from the Beagle cruise for providing us in situ data used in this first validation exercise. In situ measurements were also obtained from the SeaBASS archive at the Goddard space flight center.