Optical detection of a <i>Noctiluca scintillans</i> 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

Development and application of an algorithm for detecting <i>Phaeocystis globosa</i> blooms in the Case 2 Southern North Sea waters

While mapping algal blooms from space is now well-established, mapping undesirable algal blooms in eutrophicated coastal waters raises further challenge in detecting individual phytoplankton species. In this paper, an algorithm is developed and tested for detecting Phaeocystis globosa blooms in the Southern North Sea. For this purpose, we first measured the light absorption properties of two phytoplankton groups, P. globosa and diatoms, in laboratory-controlled experiments. The main spectral difference between both groups was observed at 467 nm due to the absorption of the pigment chlorophyll c3 only present in P. globosa, suggesting that the absorption at 467 nm can be used to detect this alga in the field. A Phaeocystis-detection algorithm is proposed to retrieve chlorophyll c3 using either total absorption or water-leaving reflectance field data. Application of this algorithm to absorption and reflectance data from Phaeocystis-dominated natural communities shows positive results. Comparison with pigment concentrations and cell counts suggests that the algorithm can flag the presence of P. globosa and provide quantitative information above a chlorophyll c3 threshold of 0.3 mg m-3 equivalent to a P. globosa cell density of 3 × 106 cells L-1. Finally, the possibility of extrapolating this information to remote sensing reflectance data in these turbid waters is evaluated

Development and application of an algorithm for detecting Phaeocystis globosa blooms in the Case 2 Southern North Sea waters

While mapping algal blooms from space is now well-established, mapping undesirable algal blooms in eutrophicated coastal waters raises further challenge in detecting individual phytoplankton species. In this paper, an algorithm is developed and tested for detecting Phaeocystis globosa blooms in the Southern North Sea. For this purpose, we first measured the light absorption properties of two phytoplankton groups, P. globosa and diatoms, in laboratory-controlled experiments. The main spectral difference between both groups was observed at 467 nm due to the absorption of the pigment chlorophyll c3 only present in P. globosa, suggesting that the absorption at 467 nm can be used to detect this alga in the field. A Phaeocystis-detection algorithm is proposed to retrieve chlorophyll c3 using either total absorption or water-leaving reflectance field data. Application of this algorithm to absorption and reflectance data from Phaeocystis-dominated natural communities shows positive results. Comparison with pigment concentrations and cell counts suggests that the algorithm can flag the presence of P. globosa and provide quantitative information above a chlorophyll c3 threshold of 0.3 mg m−3 equivalent to a P. globosa cell density of 3 × 106 cells L−1. Finally, the possibility of extrapolating this information to remote sensing reflectance data in these turbid waters is evaluated

A review on substances and processes relevant for optical remote sensing of extremely turbid marine areas, with a focus on the Wadden Sea

The interpretation of optical remote sensing data of estuaries and tidal flat areas is hampered by optical complexity and often extreme turbidity. Extremely high concentrations of suspended matter, chlorophyll and dissolved organic matter, local differences, seasonal and tidal variations and resuspension are important factors influencing the optical properties in such areas. This review gives an overview of the processes in estuaries and tidal flat areas and the implications of these for remote sensing in such areas, using the Wadden Sea as a case study area. Results show that remote sensing research in extremely turbid estuaries and tidal areas is possible. However, this requires sensors with a large ground resolution, algorithms tuned for high concentrations of various substances and the local specific optical properties of these substances, a simultaneous detection of water colour and land-water boundaries, a very short time lag between acquisition of remote sensing and in situ data used for validation and sufficient geophysical and ecological knowledge of the area. © 2010 The Author(s)

Erratum to “Bio-optical characteristics and primary productivity during upwelling and non-upwelling conditions in a highly productive coastal ecosystem off central Chile (~36°S)” [Deep-Sea Research II 51 (2004) 2413–2426]

SCOPUS: er.jinfo:eu-repo/semantics/publishe

Validation of MERIS water products in the Southern North Sea: 2002-2008

This paper describes the validation of MERIS water products for the Southern North Sea for the period July 2002 to September 2008. During this period, 39 matchups were obtained for the parameters water-leaving reflectance spectra, chlorophyll a concentration and total suspended matter concentration, of which 12 are in optimal conditions. Previous validation results reported for 2002-5 are updated to 2008. Conclusions are largely reinforced since the MERIS processor has not changed. In particular it is recommended to improve estimation of the spectral slope of aerosol reflectance in turbid waters. Some image artifacts are noted including noisy low chlorophyll data. Inherent optical property data is analysed and compared to the assumptions used for derivation of the MERIS products. Turbidity has been added to the in situ parameter set, strengthening quality control of water sample analysis

Influence of suspended particle concentration, composition and size on the variability of inherent optical properties of the Southern North Sea

Suspended particles and the relationships between their concentration, composition and size with optical properties (light absorption, and attenuation in the visible and near-infrared spectral regions) were investigated in transects performed from the Belgian to the English coasts of the Southern North Sea. Results individualize three geographical zones in the domain, each one with specific biogeochemical and optical properties: Scheldt coastal zone (SCZ), Middle of the Southern North Sea (MSNS) and Thames coastal zone (TCZ). Concentrations of organic (inorganic) particles were always higher in the SCZ (TCZ). The load of particles in the MSNS was low and dominated by organic forms. The spectral shape of particle attenuation showed a wide range from negative to positive slopes. Particle size distributions were power-law shaped along the coasts (especially in the TCZ) but bimodal in the MSNS notably during the spring phytoplankton bloom. This bimodal size distribution and more precisely a size peak around 7µm resulted in an unexpected negative spectral slope of the particle attenuation coefficient. The variations in the particulate mass-specific IOPs between the three regions were maintained over seasonal variations. The implications in terms of remote sensing inversion of IOPs into biogeochemical parameters, such as chlorophyll a and total suspended matter, in coastal waters are discussed

Hyperspectral and multispectral ocean color inversions to detect <i>Phaeocystis globosa</i> blooms in coastal waters

Identification of phytoplankton groups from space is essential to map and monitor algal blooms in coastal waters, but remains a challenge due to the presence of suspended sediments and dissolved organic matter which interfere with phytoplankton signal. On the basis of field measurements of remote sensing reflectance (Rrs(lambda)), bio-optical parameters, and phytoplankton cells enumerations, we assess the feasibility of using multispectral and hyperspectral approaches for detecting spring blooms of Phaeocystis globosa (P. globosa). The two reflectance ratios (Rrs(490)/Rrs(510) and Rrs(442.5)/Rrs(490)), used in the multispectral inversion, suggest that detection of P. globosa blooms are possible from current ocean color sensors. The effects of chlorophyll concentration, colored dissolved organic matter (CDOM), and particulate matter composition on the performance of this multispectral approach are investigated via sensitivity analysis. This analysis indicates that the development of a remote sensing algorithm, based on the values of these two ratios, should include information about CDOM concentration. The hyperspectral inversion is based on the analysis of the second derivative of Rrs(lambda) (d lambda2 Rrs). Two criteria, based on the position of the maxima and minima of dlambda2 Rrs, are established to discriminate the P. globosa blooms from diatoms blooms. We show that the position of these extremes is related to the specific absorption spectrum of P. globosa and is significantly correlated with the relative biomass of P. globosa. This result confirms the advantage of a hyperspectral over multispectral inversion for species identification and enumeration from satellite observations of ocean color

Hyperspectral versus multispectral remote sensing approach to detect phytoplankton blooms in coastal waters : application to a Phaeocystis bloom.

International audienc