Analysis of SeaWiFS imagery over the southwestern Atlantic Ocean during the March 2002 R/V IOFFE cruise

Abstract

SeaWiFS ocean-colour products for the Southwestern Atlantic Ocean are evaluated in comparison with in situ bio-optical data collected during the March 10-12, 2002 cruise from Ushuaia to Uruguay. Radiometric measurements and surface water sampling were carried out at 14 stations. The in situ dataset included HPLC chlorophyll-a concentration (chl-a), a ph ( ) spectral absorption coefficients of phytoplankton, suspended particles, and a cdom ( ) dissolved organic matter, R RS remote sensing reflectance, AOT and aerosol optical thickness. In general, the SeaWiFS-derived and SIMBAD measured AOT were low, but with a good agreement within SIMBAD uncertainty errors. The SeaWiFS-derived R RS was systematically underestimated, but still with good fits. The were high indicating the presence of small size cells with a low packaging effect. The HPLC pigment composition did not show strong variations amongst the sampled points, with communities most probably dominated by small cells. The phytoplankton community was more homogeneous in the southern stations, than in the northernmost stations influenced by the mixing of the Brazil and Malvinas Currents and the La Plata River discharge. The analyzes of the in situ a cdom (440) characterized the sampling stations as CDOM rich waters. All SeaWiFS chl-a algorithms showed reasonable performances. The empirical algorithms overestimated lower chl-a while underestimated higher concentrations. The GSM01 semi-analytical algorithm underestimated most chl-a values, while CARDER underestimated only the lower concentrations. It is expected that the accuracy of chlorophyll retrievals in coastal areas of the BMC can be improved by a proper tuning of the semi-analytical models with regional inherent optical properties measurements.