A new regional algorithm for estimating chlorophyll a in the Alborán Sea (Mediterranean Sea) from MODIS-Aqua satellite imagery

Abstract

The utility of three different algorithms for retrieving surface chlorophyll-a values from satellite images of MODIS-Aqua is tested in the northern Alboran Sea. The available global algorithm to calculate chlorophyll-a from reflectance of MODIS-Aqua (OC3M) overestimates the surface chlorophyll-a in the study area. Another regional algorithm specifically developed for the Mediterranean Sea (MedOC3) improves the estimates although the best outcome is obtained with OC5, which was developed for Atlantic coastal waters. The three tested algorithms perform worse at in situ chlorophyll-a concentrations higher than 1 mg m−3 and exhibit uncertainty levels higher than 35% for this range of concentrations. A new algorithm (ALBOC3) is proposed which produces a good estimation of the in situ chlorophyll-a for the whole range of concentrations normally registered in the study area (0.1–3.5 mg m−3). We hypothesize that the particular bio-optical features of the northern Alboran Sea phytoplankton explain the poor functioning of the published algorithms that have been tested in this work.