Evaluation of the MERIS marine products in coastal and oceanic waters off Cape Sagres on the south-west coast of Portugal

In-water constituents such as chlorophyll a, total suspended matter and yellow substances, as well as radiometric data sets from field measurements with a Satlantic hyperspectral radiometer were used to evaluate the performance of Medium Resolution Imaging Spectrometer (MERIS) sensor on the ENVISAT satellite, from inshore to offshore sites on the south west coast of Portugal. It was evaluate the performance of the Regular measurements of these parameters were taken from this region between September 2008 and July 2009 covering both Case 1 and Case 2 waters. Also was evaluate the recent developments towards improving the processing protocols for MERIS data including: the ICOL (Improved Contrast between Ocean and Land) processor; the new vicarious adjustment in the near infrared; and, most recently, the implementation of the MEGS 8 processor. Eight images were obtained under cloud free conditions, without flags for high glint, ice haze and low sun during this sampling period. Water-leaving reflectances (ρw) were estimated from downwelling Es (λ) and upwelling Lu (λ) spectral irradiances, and compared with MERIS ρw. The values of ρw were processed according to the MERIS in situ measurement protocols, before they could be compared with the MERIS data. A previous study in this area (Cristina et al., 2009) shows that are still problems with the calibrating the algorithm that links remote sensing data with in situ measurements, particularly at the coastal site where there are adjacency effects from land on the reflectance data observed by the satellite sensor. In this study ICOL processor was applied to correct this problem and improve processing on the inshore station (Station A). However the improvement was not so significant for some of the “match-ups” days. The MERIS ρw and the MERIS water products processed by the MEGS 8 didn’t improve the agreement with the in situ measurements as was expected, even with the new vicarious adjustment for the infrared wavelengths. In general, these results show that some corrections most be taken under MEGS 8 processor before coming publically available.