OPTICAL DETECTION OF A NOCTILUCA SCINTILLANS BLOOM

Noctiluca scintillans blooms are often observed as reddish patches in Belgian waters in June-July in calm weather. The possibility of mapping these blooms is investigated here. In June 2005 a dataset of in situ measured reflectance spectra, airborne hyperspectral images, experimental reflectance and absorption spectra of Noctiluca scintillans was collected. The strong optical signature of dense Noctiluca scintillans blooms suggests that mapping these blooms should be feasible. A detection algorithm is proposed based on a combination of a high reflectance threshold with a condition of sharp increase in reflectance in the range 520-580 nm. This algorithm will detect only intense blooms but should distinguish between Noctiluca scintillans and both intense phytoplankton blooms and very turbid water. Noctiluca scintillans detection by optical sensors mounted on ships and airplanes has been confirmed for the June 2005 bloom in Belgian waters. Detection from satellites should also be feasible but only if suitable wavelengths are available and only if the spatial resolution is sufficiently high. The optical properties of this species are thought to be related to gut content. The applicability of this algorithm to other regions and situations therefore remains to be tested.

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