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Quantifying ocean colour properties has evolved over the past two decades from being able to merely detect their
biological activity to the ability to estimate chlorophyll concentration using optical satellite sensors like MODIS and
MERIS. The production of chlorophyll spatial distribution maps is a good indicator of plankton biomass (primary
production) and is useful for the tracing of oceanographic currents, jets and blooms, including harmful algal blooms
(HABs). Depending on the type of HABs involved and the environmental conditions, if their concentration rises above a
critical threshold, it can impact the flora and fauna of the aquatic habitat through the introduction of the so called "red
tide" phenomenon. The estimation of chlorophyll concentration is derived from quantifying the spectral relationship
between the blue and the green bands reflected from the water column. This spectral relationship is employed in the
standard ocean colour chlorophyll-a (Chlor-a) product, but is incapable of detecting certain macro-algal species that float
near to or at the water surface in the form of dense filaments or mats. The ability to accurately identify algal formations
that sometimes appear as oil spill look-alikes in satellite imagery, contributes towards the reduction of false-positive
incidents arising from oil spill monitoring operations. Such algal formations that occur in relatively high concentrations
may experience, as in land vegetation, what is known as the "red-edge" effect. This phenomena occurs at the highest
reflectance slope between the maximum absorption in the red due to the surrounding ocean water and the maximum
reflectance in the infra-red due to the photosynthetic pigments present in the surface algae. A new algorithm termed the
surface algal bloom index (SABI), has been proposed to delineate the spatial distributions of floating micro-algal species
like for example cyanobacteria or exposed inter-tidal vegetation like seagrass. This algorithm was specifically modelled
to adapt to the marine habitat through its inclusion of ocean-colour sensitive bands in a four-band ratio-based
relationship. The algorithm has demonstrated high stability against various environmental conditions like aerosol and sun
glint.
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