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National audienceLa mise en place de plusieurs réseaux nationaux d’observation in situ (e.g. SOMLIT, REPHY, COAST-HF,..) ainsi que les récents développements méthodologiques en terme d’observation spatiale dite « couleur de l’eau » à... more
National audienceLa mise en place de plusieurs réseaux nationaux d’observation in situ (e.g. SOMLIT, REPHY, COAST-HF,..) ainsi que les récents développements méthodologiques en terme d’observation spatiale dite « couleur de l’eau » à l’échelle nationale permettent désormais de suivre la dynamique des eaux côtières françaises à de multiples échelles spatiales ou temporelles. L’exploitation de ces informations terrain ou satellite, généralement effectuée de manière indépendante, doit cependant faire face à différentes limitations propres aux observations in situ (e.g. faible emprise spatiale : données localisées et nombre de stations limité au sein d’un même site ou le long du littoral) ou aux données satellitaires (e.g. incertitudes sur les produits, fréquence d’acquisition, couverture temporelle réduite). Le projet OSYNICO (TOSCA/CNES) a été défini dans ce contexte et a pour objectif général de démontrer l’avantage de la complémentarité des observations in situ et satellite pour 1) décrire les évolutions à long terme (évolution des signaux moyens et des oscillations saisonnières) des caractéristiques biogéochimiques des eaux côtières françaises (de l’échelle locale à l’échelle synoptique) 2) d’apprécier l’impact des évènements climatiques extrêmes sur ces écosystèmes côtiers. Les bases de données et outils/métriques mis en place dans le cadre du projet pour la comparaison des dynamiques observées pour des variables clés (e.g. Chla, MES, POC) via les observations in situ et couleur seront présentés. Un focus sera effectué sur les premiers résultats obtenus aux échelles saisonnières et interannuelles
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The concept of phytoplankton functional types has emerged as a useful approach to classifying phytoplankton and can be used to obtain a better understanding of ecological and biogeochemical processes. Recent developments in remote sensing... more
The concept of phytoplankton functional types has emerged as a useful approach to classifying phytoplankton and can be used to obtain a better understanding of ecological and biogeochemical processes. Recent developments in remote sensing provide a unique opportunity to study some phytoplankton functional types through analysis of ocean-colour data. Remote sensing of phytoplankton functional types is an emerging field, whose potential is not fully realised, nor its limitations clearly established. This report provides an overview of progress to date, examining the advantages and limitations of various methods, and providing suggestions for further development.
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André Valente, Shubha Sathyendranath , Vanda Brotas , Steve Groom, Michael Grant, Malcolm Taberner, David Antoine, Robert Arnone, William M. Balch, Kathryn Barker, Ray Barlow, 5 Simon Bélanger, Jean-François Berthon, Şükrü Beşiktepe,... more
André Valente, Shubha Sathyendranath , Vanda Brotas , Steve Groom, Michael Grant, Malcolm Taberner, David Antoine, Robert Arnone, William M. Balch, Kathryn Barker, Ray Barlow, 5 Simon Bélanger, Jean-François Berthon, Şükrü Beşiktepe, Yngve Borsheim, Astrid Bracher, Vittorio Brando, Elisabetta Canuti, Francisco Chavez, Andrés Cianca, Hervé Claustre, Lesley Clementson, Richard Crout, Robert Frouin, Carlos García-Soto, Stuart W. Gibb, Richard Gould, Stanford B. Hooker, Mati Kahru, Milton Kampel, Holger Klein, Susanne Kratzer, Raphael Kudela, Jesus Ledesma, Hubert Loisel, Patricia Matrai, David McKee, Brian G. 10 Mitchell, Tiffany Moisan, Frank Muller-Karger, Leonie O'Dowd, Michael Ondrusek, Trevor Platt, Alex J. Poulton, Michel Repecaud, Thomas Schroeder, Timothy Smyth, Denise SmytheWright, Heidi M. Sosik, Michael Twardowski, Vincenzo Vellucci, Kenneth Voss, Jeremy Werdell, Marcel Wernand, Simon Wright, Giuseppe Zibordi 15
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In the frame of GlobCoast project (11/2012-11/2015), funded by the French National Research Agency (ANR), a completely new dataset covering the global coastal waters has been processed. For MERIS period (2002-2012), SPM, Chlorophyl,... more
In the frame of GlobCoast project (11/2012-11/2015), funded by the French National Research Agency (ANR), a completely new dataset covering the global coastal waters has been processed. For MERIS period (2002-2012), SPM, Chlorophyl, acdom, DOC, Kd, anw and bbp, are now available at global scale at 1 km resolution. Monthly climatologies (with variation coefficient), eight days and monthly means are available. Results of advanced time series analysis from census-X11 method (trend, seasonal and irregular contribution) are also available. The data, projected on a sinusoidal equal-area grid, have been filtered to only keep the coastal waters. Even with filtering each image has a potential of 64 millions of pixels. To deal with this a specific storage format have been defined in order to optimize both processing and storage of this dataset. This format and the data model used for storage, using Hierarchical Data Format (HDF), is presented. This data set is made available through a web bas...
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The primary objectives of this study were: 1) to re-examine the causes of the color anomaly found in ultra-oligotrophic waters of the Mediterranean Sea by adding measurements of the particulate backscattering coefficient, bbp, and 2) to... more
The primary objectives of this study were: 1) to re-examine the causes of the color anomaly found in ultra-oligotrophic waters of the Mediterranean Sea by adding measurements of the particulate backscattering coefficient, bbp, and 2) to test whether or not diurnal cycles in bbp could be observed. These are relevant questions within the scope off BG, and I believe that both of these objectives were well met. This is an excellent paper that carefully examines many details of the data that might escape notice if given only a casual examination. It is definitely a paper that will make a difference in studies of bio-optics and will be cited frequently.
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Using biogeochemical-Argo float measurements, we propose, for the first time, an optical proxy for particulate organic nitrogen concentration (PON) in the Western Tropical South Pacific, an area influenced by dinitrogen (N2) fixation. Our... more
Using biogeochemical-Argo float measurements, we propose, for the first time, an optical proxy for particulate organic nitrogen concentration (PON) in the Western Tropical South Pacific, an area influenced by dinitrogen (N2) fixation. Our results show a significant relationship between the backscattering coefficient at 700 nm (bbp) and PON, especially when the latter is measured using the wet oxidation method (R2=0.87). bbp may be used to estimate PON concentrations (PONopt) between 0.02 and 0.95 µM, allowing for unprecedented monitoring using autonomous profiling floats. The bbp vs PON relationship can be used to study phytoplanktonic biomass dynamics at relevant seasonal temporal scales, with clear evidence of PONopt as a proxy of phytoplanktonic biomass, at least for this specific area. Temporal analyses of PONopt show significant increases (from 0.16 to 0.80 µM) likely related to new production associated to N2 fixation events measured during stratification periods in the Melane...
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VNREDSat-1 is the first Vietnamese satellite allowing the survey of environmental parameters such as vegetation and water coverages, or surface water quality at medium spatial resolution (from 2.5 to 10 meters depending on the considered... more
VNREDSat-1 is the first Vietnamese satellite allowing the survey of environmental parameters such as vegetation and water coverages, or surface water quality at medium spatial resolution (from 2.5 to 10 meters depending on the considered channel). The NAOMI sensor on board VNREDSat-1 has the required spectral bands to assess the suspended particulate matter concentration, SPM. Because recent studies have shown that the remote sensing reflectance, Rrs(), at the blue (450 – 520 nm), green (530 – 600 nm), and red (620 – 690 nm) spectral bands can be assessed from NAOMI with a good accuracy, the present study is dedicated to the development and validation of an algorithm (hereafter referred to as V1SPM) to assess SPM from Rrs() over inland and coastal waters of Vietnam. For that purpose, an in situ data set of hyper-spectral Rrs() and SPM (from 0.47 to 240.14 g.m-3) measurements collected at 205 coastal and inland stations has been gathered. Among the different approaches, including ...
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Recently, different algorithms have been developed to assess near-surface particulate organic matter (POC) concentration over coastal waters. In this study, we gathered an extensive in situ dataset representing various contrasted... more
Recently, different algorithms have been developed to assess near-surface particulate organic matter (POC) concentration over coastal waters. In this study, we gathered an extensive in situ dataset representing various contrasted bio-optical coastal environments at low, medium, and high latitudes, with various bulk particulate matter chemical compositions (mineral-dominated, 50% of the data set, mixed, 40%, or organic-dominated, 10%). The dataset includes 606 coincident measurements of POC concentration and remote-sensing reflectance, Rrs, with POC concentrations covering three orders of magnitude. Twelve existing algorithms have then been tested on this data set, and a new one was proposed. The results show that the performance of historical algorithms depends on the type of water, with an overall low performance observed for mineral-dominated waters. Furthermore, none of the tested algorithms provided satisfactory results over the whole POC range. A novel approach was thus develop...
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The Sentinel-3A satellite was launched on 16 February 2016 with the Ocean and Land Colour Instrument (OLCI-A) on-board for the study of ocean color. The accuracy of ocean color parameters depends on the atmospheric correction algorithm... more
The Sentinel-3A satellite was launched on 16 February 2016 with the Ocean and Land Colour Instrument (OLCI-A) on-board for the study of ocean color. The accuracy of ocean color parameters depends on the atmospheric correction algorithm (AC). This processing consists of removing the contribution of the atmosphere from the total measured signal by the remote sensor at the top of the atmosphere. Five ACs: the baseline AC, the Case 2 regional coast color neural network AC, its alternative version, the Polymer AC, and the standard NASA AC, are inter-compared over two bio-optical contrasted French coastal waters. The retrieved water-leaving reflectances are compared with in situ ocean color radiometric measurements collected using an ASD FielSpec4 spectrometer. Statistical and spectral analysis were performed to assess the best-performing AC through individual (relative error (RE) at 412 nm ranging between 23.43 and 57.31%; root mean squared error (RMSE) at 412 nm ranging between 0.0077 a...
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The bulk backscattering ratio ( b b p ˜ ) is commonly used as a descriptor of the bulk real refractive index of the particulate assemblage in natural waters. Based on numerical simulations, we analyze the impact of modeled structural... more
The bulk backscattering ratio ( b b p ˜ ) is commonly used as a descriptor of the bulk real refractive index of the particulate assemblage in natural waters. Based on numerical simulations, we analyze the impact of modeled structural heterogeneity of phytoplankton cells on b b p ˜ . b b p ˜ is modeled considering viruses, heterotrophic bacteria, phytoplankton, organic detritus, and minerals. Three case studies are defined according to the relative abundance of the components. Two case studies represent typical situations in open ocean, oligotrophic waters, and phytoplankton bloom. The third case study is typical of coastal waters with the presence of minerals. Phytoplankton cells are modeled by a two-layered spherical geometry representing a chloroplast surrounding the cytoplasm. The b b p ˜ values are higher when structural heterogeneity is considered because the contribution of coated spheres to light backscattering is higher than homogeneous spheres. The impact of heterogeneity i...
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The bulk backscattering ratio ($\tilde{b_{bp}}$) is commonly used as a descriptor of the bulk real refractive index of the particulate assemblage in natural waters. Based on numerical simulations, we analyze the impact of heterogeneity of... more
The bulk backscattering ratio ($\tilde{b_{bp}}$) is commonly used as a descriptor of the bulk real refractive index of the particulate assemblage in natural waters. Based on numerical simulations, we analyze the impact of heterogeneity of phytoplankton cells on $\tilde{b_{bp}}$. $\tilde{b_{bp}}$ is modeled considering viruses, heterotrophic bacteria, phytoplankton, detritus, and minerals. Three study cases are defined according to the relative abundance of these different components. Two study cases represent typical situations in open ocean, outside (No-B/No-M) and inside bloom (B/No-M). The third study case is typical of coastal waters with the presence of minerals. Phytoplankton cells are modeled by a two-layered spherical geometry representing a chloroplast surrounding the cytoplasm. The $\tilde{b_{bp}}$ values are higher when heterogeneity is considered because the contribution of coated spheres to backscattering is higher than homogeneous spheres. The impact of heterogeneity i...
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After the exponential growth phase, variability in the scattering efficiency of phytoplankton cells over their complete life cycle is not well characterised. Bulk measurements are impacted by senescent cells and detritrus. Thus the... more
After the exponential growth phase, variability in the scattering efficiency of phytoplankton cells over their complete life cycle is not well characterised. Bulk measurements are impacted by senescent cells and detritrus. Thus the analysis of the evolution of the optical properties thanks to their morphological and/or intra-cellular variations remains poorly studied. Using the Cytosense flow cytometer (CytoBuoy b.v., NL), the temporal course of the forward and sideward efficiencies of two phytoplankton species (Thalassiosira pseudonana and Chlamydomonas concordia) were analyzed during a complete life-cycle. These two species differ considerably from a morphological point of view. Over the whole experiment, the forward and sideward efficiencies of Thalassiosira pseudonana were, on average, respectively 2.2 and 1.6 times higher than the efficiencies of Chlamydomonas concordia. Large intra-species variability of the efficiencies were observed over the life cycle of the considered spec...
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Research Interests: Environmental Science, Geology, Computer Science, Remote Sensing, Algorithm, and 12 moreAtmospheric Correction, Airborne Particulates, Ocean Color, Optical Properties, Chesapeake Bay, Seawifs, Coastal waters, Colored Dissolved Organic Matter, Suspended Particulate Matter, In Situ Measurements, Southern North Sea, and Biogeochemical Cycle
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ABSTRACT The particulate backscattering coefficient and the degree of polarization provide a means to study and characterize the nature of suspended marine particles. Here, we show that such information may be retrieved from remote sensing.
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During spring and summer 2004, intensive field campaigns were conducted in the Eastern English Channel. This region is characterized by relatively intense phytoplankton blooms, low bathymetry, strong tide ranges and great river inputs.... more
During spring and summer 2004, intensive field campaigns were conducted in the Eastern English Channel. This region is characterized by relatively intense phytoplankton blooms, low bathymetry, strong tide ranges and great river inputs. The sampling period accounts for episodic blooms of prymnesiophyceae Phaeocystis globosa and diatoms. Hyperspectral radiometric measurements (TRIOS; 350-950 nm, with a 3 nm spectral resolution) were concurrently
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The fine-scale study of the diffuse attenuation coefficient, Kd(lambda), of the spectral solar downward irradiance is only feasible by ocean color remote sensing. Several empirical and semi-analytical methods exist. However, most of... more
The fine-scale study of the diffuse attenuation coefficient, Kd(lambda), of the spectral solar downward irradiance is only feasible by ocean color remote sensing. Several empirical and semi-analytical methods exist. However, most of tthese models are generally applicable for clear open ocean waters. They show limitations when applied to coastal waters. A new empirical method based on neural networks has been developed using a relationship between the remote-sensing reflectances between 412 and 670 nm and Kd(490), for the SeaWiFS ocean color remote sensor. The architecture of the neural network has been defined using synthetical and in situ dataset and the optimal design is a tow hidden layer neural network with 4 neurons of the first layer and three on the second layer. The comparison with the SeaWiFS empirical algorithms shows similar retrievals accuracies for low values of Kd(490) (i.e. <0.20 m-1) and better estimates for greater values of and Kd(490). The new model is suitable for open water but also for turbid waters and does not show the limitations of the empirical method. The new model is more general that the empirical methods.
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The SIMBADA radiometer was designed to check the radiometric calibration of satellite ocean-color sensors and evaluate the atmospheric correction of ocean-color imagery. It measures marine reflectance and aerosol optical thickness in 11... more
The SIMBADA radiometer was designed to check the radiometric calibration of satellite ocean-color sensors and evaluate the atmospheric correction of ocean-color imagery. It measures marine reflectance and aerosol optical thickness in 11 spectral bands covering the spectral range 350 to 870 nm. Aerosol optical thickness is obtained by viewing the sun disk and marine reflectance by viewing the ocean surface
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The impact of the inherent optical properties (IOP) variability on the chlorophyll, Chl, retrieval from ocean color remote sensing algorithms is analyzed from an in situ data set covering a large dynamic range. The effect of the... more
The impact of the inherent optical properties (IOP) variability on the chlorophyll, Chl, retrieval from ocean color remote sensing algorithms is analyzed from an in situ data set covering a large dynamic range. The effect of the variability of the specific phytoplankton absorption coefficient, a(phy)/Chl, specific particulate backscattering coefficient, b(bp)/Chl, and colored detrital matter absorption to non-water absorption ratio, a(cdm)/a(nw), on the performance of standard operational algorithms is examined. This study confirms that empirical algorithms are highly dependent on the specifics IOP values (especially b(bp)/Chl and a(cdm)/a(nw)): Chl is over-estimated in waters with specific IOP values higher than averaged values, and vice versa. These results clearly indicate the necessity to account for the influence of the specific IOP variability in Chl retrieval algorithms.
Research Interests: Environmental Science, Algorithms, Remote Sensing, Colorimetry, Environmental Monitoring, and 15 morePhytoplankton, Medicine, Color, Chlorophyll, In situ, Ocean Color, Optical physics, Optics and Photonics, Reproducibility of Results, Colored Dissolved Organic Matter, Statistical models, Inherent Optical Properties, Electrical And Electronic Engineering, Chlorophyll a, and Oceans and Seas
The in-water radiance é eld has been computed in typical Case 2 waters by using radiative transfer models and appropriate inherent optical properties (IOPs) combined with realistic boundary conditions. In particular, the bi-direc- tional... more
The in-water radiance é eld has been computed in typical Case 2 waters by using radiative transfer models and appropriate inherent optical properties (IOPs) combined with realistic boundary conditions. In particular, the bi-direc- tional structure of the subsurface upward è ux has been investigated in view of remote sensing applications related to ocean colour. In Case 2 waters, the IOPs are not controlled by the phytoplankton (or chlorophyll) concentration; rather they are essentially determined by the abundance of terrigenous optically active materials, either particulate or dissolved. Based on é eld data and related IOPs, two extreme situations were selected as representative instances of sediment- dominated and yellow-substance-dominated Case 2 waters. This study shows that even in very turbid natural waters, the upward radiance é eld is not isotropic and remains Sun-angle dependent. More than 100 successive events are needed to reach a quasi-isotropic, illumination independent,...
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Recent satellite observations of Rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave-induced upwelling could stimulate photosynthesis. Instead, we show that chlorophyll maxima are located in... more
Recent satellite observations of Rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave-induced upwelling could stimulate photosynthesis. Instead, we show that chlorophyll maxima are located in abnormally warm water, in Rossby wave–induced convergences. This excludes inputs of nutrients from deeper water. We argue that the sea color anomalies are not caused by chlorophyll but by floating particles evolved from the ecosystem and accumulated by Rossby waves, acting as “marine hay rakes,” in convergence zones. Such processes may be determinant for the distribution of living organisms in oligotrophic areas.