Evaluation of SeaWiFS and MODIS chlorophyll‐a products in the Argentinean Patagonian Continental Shelf (38° S–55° S)

Abstract

Field measurements of surface chlorophyll‐a concentration were used to evaluate for the first time the performance of the standard Moderate Resolution Imaging Spectroradiometer (MODIS) and both standard and regional Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean colour algorithms in the Patagonian Continental Shelf (PCS) between 38° S and 55° S. The results showed that the regional algorithms did not significantly improve the global algorithm estimates. Moreover, the SeaWiFS OC4v4 algorithm, National Aeronautics and Space Administration (NASA) standard chlorophyll product, showed the best performance among all the algorithms examined. Nonetheless, all the global and local algorithms analysed showed uncertainties dependent on chlorophyll concentration. Low chlorophyll‐a concentration values tended to be overestimated and high values tended to be underestimated. A regional analysis within the PCS showed that higher uncertainties are found in the homogeneous side of the tidal fronts present in the PCS, in areas suggested to be optically complex case 2 waters, while a better result (less bias) was obtained in the southern mid‐shelf region. We discuss the probable reasons and provide possible explanations of the regional differences in the performance of the algorithms.

Acknowledgements

A.I. Dogliotti would like to thank R. Frouin and G. Giribet for useful conversations and constructive comments on the manuscript, S. Bélanger for helpful suggestions on an earlier draft and the IOCCG and POGO for economical support in training programmes. Anonymous reviewers are acknowledged for their helpful comments. This work was supported by CONICET, Agencia Nacional de Promoción Científica y Tecnológica through grants PICTO 6524/1108/03‐ANPCyT 01‐11563 to I.R.S. and PICT03‐15221 to D.A.G. The Global Environmental Facility (GEF) grant 28385 to D.A.G. and CONICET fellowships to A.I. Dogliotti and G.O. Almandoz. We thank the NASA SeaWiFS Project and the NASA/GSFC/DAAC for the production and distribution of SeaWiFS data, respectively. Field work was conducted within the framework of a cooperative research program (ARGAU, Programme de coopération avec la ARGentine pour l'étude de l'océan Atlantique AUstral) between the Instituto Antártico Argentino, the Laboratoire de Biogéochimie et Chimie Marines at the Université Pierre et Marie Curie in Paris (France), and the Servicio de Hidrografía Naval (Argentina) from 2002 to 2004. We wish to thank all the persons participating in sample collection, especially to A. Ulrich for Chl‐a determinations. Our thanks also to the crew members of the Almirante Irizar.