LONG-TERM DISTRIBUTION OF CHLOROPHYLL A FROM MERIS FR DATA USING LOCALLY ADJUSTED ALGORITHMS (NW SPAIN)

摘要

MERIS images have proven to be a valuable tool for monitoring chlorophyll a on the Galician (NW Spain) coastal area, which is periodically affected by upwelling events usually related to harmful algae blooms. The chlorophyll-a distribution, including monthly anomalies, was analysed from 9 years of MERIS data (2003-2012) for this area. Regionally tuned algorithms (Regional neural network for rias Baixas or NNRB), developed and tested in previous works by the authors of this study, were applied to this long series of MERIS images for the retrieval of chlorophyll a. Given that Galician waters are considered as optically complex, a fuzzy c-mean clustering technique (FCM) was first applied to reflectance data in order to define the zones where NNRB produces reliable results. The relationship of MERIS chlorophyll a data with upwelling events and harmful algae blooms was also discussed. This work was developed in the framework of the project PURGADEMAR, which aims to develop an operational monitoring system for Pseudo-nitzschia blooms in the Galician rias.