Using the SISCAL in situ measurements for the validation of the MERIS Algal Pigment Indices I and II

In the frame of the EC-funded project SISCAL (Satellite-based Information System on Coastal Areas and Lakes), in situ campaigns have been executed in three coastal areas in the Baltic Sea, North-Eastern Atlantic and the Eastern Mediterranean as well as in a lake in North-Eastern Germany. The aim of these campaigns was to obtain measurements of the chlorophyll concentration for the validation of MERIS (Medium Resolution Imaging Spectrometer) data products. Between May and September 2002, in situ measurements have been performed concomitantly to thirteen MERIS overpasses. As of December 2002, MERIS Level-2 ocean products could be made available for six of the thirteen overpasses. At the specific in situ sampling sites, ocean products were available in four of the six MERIS data sets. On a pixel-by-pixel basis, three / four match-ups are available for Algal Pigment Index (API) I / II. The following preliminary conclusions can be drawn from the SISCAL validation activities: 1) API I shows a better dynamic resolution than does API II and reveals such more detailed dynamic structure, especially in oligotrophic areas, 2) in open ocean areas, API II values are larger (mostly by a factor of roughly two) than the API I values and appear to be overestimated, 3) in coastal areas influenced by significant CDOM concentrations, API II gives better results than API I.