52 research outputs found
An Overview of Approaches and Challenges for Retrieving Marine Inherent Optical Properties from Ocean Color Remote Sensing
Ocean color measured from satellites provides daily global, synoptic views of spectral water-leaving reflectances that can be used to generate estimates of marine inherent optical properties (IOPs). These reflectances, namely the ratio of spectral upwelled radiances to spectral downwelled irradiances, describe the light exiting a water mass that defines its color. IOPs are the spectral absorption and scattering characteristics of ocean water and its dissolved and particulate constituents. Because of their dependence on the concentration and composition of marine constituents, IOPs can be used to describe the contents of the upper ocean mixed layer. This information is critical to further our scientific understanding of biogeochemical oceanic processes, such as organic carbon production and export, phytoplankton dynamics, and responses to climatic disturbances. Given their importance, the international ocean color community has invested significant effort in improving the quality of satellite-derived IOP products, both regionally and globally. Recognizing the current influx of data products into the community and the need to improve current algorithms in anticipation of new satellite instruments (e.g., the global, hyperspectral spectroradiometer of the NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission), we present a synopsis of the current state of the art in the retrieval of these core optical properties. Contemporary approaches for obtaining IOPs from satellite ocean color are reviewed and, for clarity, separated based their inversion methodology or the type of IOPs sought. Summaries of known uncertainties associated with each approach are provided, as well as common performance metrics used to evaluate them. We discuss current knowledge gaps and make recommendations for future investment for upcoming missions whose instrument characteristics diverge sufficiently from heritage and existing sensors to warrant reassessing current approaches
An Overview of Approaches and Challenges for Retrieving Marine Inherent Optical Properties from Ocean Color Remote Sensing
Ocean color measured from satellites provides daily global, synoptic views of spectral water-leaving reflectancesthat can be used to generate estimates of marine inherent optical properties (IOPs). These reflectances, namelythe ratio of spectral upwelled radiances to spectral downwelled irradiances, describe the light exiting a watermass that defines its color. IOPs are the spectral absorption and scattering characteristics of ocean water and itsdissolved and particulate constituents. Because of their dependence on the concentration and composition ofmarine constituents, IOPs can be used to describe the contents of the upper ocean mixed layer. This informationis critical to further our scientific understanding of biogeochemical oceanic processes, such as organic carbonproduction and export, phytoplankton dynamics, and responses to climatic disturbances. Given their im-portance, the international ocean color community has invested significant effort in improving the quality of satellite-derived IOP products, both regionally and globally. Recognizing the current influx of data products intothe community and the need to improve current algorithms in anticipation of new satellite instruments (e.g., theglobal, hyperspectral spectroradiometer of the NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mis-sion), we present a synopsis of the current state of the art in the retrieval of these core optical properties.Contemporary approaches for obtaining IOPs from satellite ocean color are reviewed and, for clarity, separatedbased their inversion methodology or the type of IOPs sought. Summaries of known uncertainties associated witheach approach are provided, as well as common performance metrics used to evaluate them. We discuss currentknowledge gaps and make recommendations for future investment for upcoming missions whose instrumentcharacteristics diverge sufficiently from heritage and existing sensors to warrant reassessing current approaches
Satellite sensor requirements for monitoring essential biodiversity variables of coastal ecosystems
The biodiversity and high productivity of coastal terrestrial and aquatic habitats are the foundation for important benefits to human societies around the world. These globally distributed habitats need frequent and broad systematic assessments, but field surveys only cover a small fraction of these areas. Satellite-based sensors can repeatedly record the visible and near-infrared reflectance spectra that contain the absorption, scattering, and fluorescence signatures of functional phytoplankton groups, colored dissolved matter, and particulate matter near the surface ocean, and of biologically structured habitats (floating and emergent vegetation, benthic habitats like coral, seagrass, and algae). These measures can be incorporated into Essential Biodiversity Variables (EBVs), including the distribution, abundance, and traits of groups of species populations, and used to evaluate habitat fragmentation. However, current and planned satellites are not designed to observe the EBVs that change rapidly with extreme tides, salinity, temperatures, storms, pollution, or physical habitat destruction over scales relevant to human activity. Making these observations requires a new generation of satellite sensors able to sample with these combined characteristics: (1) spatial resolution on the order of 30 to 100-m pixels or smaller; (2) spectral resolution on the order of 5 nm in the visible and 10 nm in the short-wave infrared spectrum (or at least two or more bands at 1,030, 1,240, 1,630, 2,125, and/or 2,260 nm) for atmospheric correction and aquatic and vegetation assessments; (3) radiometric quality with signal to noise ratios (SNR) above 800 (relative to signal levels typical of the open ocean), 14-bit digitization, absolute radiometric calibration \u3c2%, relative calibration of 0.2%, polarization sensitivity \u3c1%, high radiometric stability and linearity, and operations designed to minimize sunglint; and (4) temporal resolution of hours to days. We refer to these combined specifications as H4 imaging. Enabling H4 imaging is vital for the conservation and management of global biodiversity and ecosystem services, including food provisioning and water security. An agile satellite in a 3-d repeat low-Earth orbit could sample 30-km swath images of several hundred coastal habitats daily. Nine H4 satellites would provide weekly coverage of global coastal zones. Such satellite constellations are now feasible and are used in various applications
RĂLE DE L'OCCUPATION DU SOL VIS Ă VIS DE LA MODĂLISATION DES FLUX ENERGĂTIQUES ET HYDRIQUES EN MILIEU URBAIN ET PĂRIURBAIN
National audienceLe projet Rosenhy vise Ă Ă©tudier lâimpact de lâoccupation du sol sur la modĂ©lisation mĂ©tĂ©orologique et hydrologique en termes de flux Ă©nergĂ©tiques et hydriques, en milieu urbain et pĂ©riurbain. Trois sites appartenant aux observatoires français OTHU et ONEVU sont au centre de ce projet. Le quartier urbain hĂ©tĂ©rogĂšne du Pin sec (Nantes), impermĂ©abilisĂ© Ă environ 45%, a fait lâobjet dâune campagne expĂ©rimentale durant le mois de juin 2012, visant Ă estimer les flux de chaleur sensible et latente avec une haute rĂ©solution spatiale et temporelle par rapport aux mesures rĂ©alisĂ©es en continu sur ce site depuis 5 ans. Deux bassins versant pĂ©riurbains (La ChĂ©zine Ă Nantes et lâYzeron Ă Lyon), avec un taux dâimpermĂ©abilisation moins important (environ 10%) mais grandissant depuis plusieurs dĂ©cennies, sont aussi Ă©tudiĂ©s. Ces deux derniers sites bĂ©nĂ©ficient dâun suivi hydromĂ©tĂ©orologique depuis 10 ans pour la ChĂ©zine et 15 ans pour lâYzeron. Sur ces trois sites, diffĂ©rentes sources de donnĂ©es dâoccupation du sol Ă diffĂ©rentes rĂ©solutions sont disponibles :diffĂ©rentes bases de donnĂ©es gĂ©ographiques communĂ©ment utilisĂ©es par la communautĂ© scientifique et les collectivitĂ©s et des donnĂ©es tĂ©lĂ©dĂ©tectĂ©es (multispectrales et hyperspectrales). Lâutilisation de ces donnĂ©es en entrĂ©e de diffĂ©rents modĂšles mĂ©tĂ©orologiques et hydrologiques implique un travail dâanalyse et de classification pour adapter les informations aux besoins des modĂšles. Dans ce projet, les diffĂ©rents modĂšles adaptĂ©s au milieu urbain ou pĂ©rirubain sont Ă©valuĂ©s et amĂ©liorĂ©s. Ainsi, les modĂšles hydrologiques pĂ©rirubains sont en dĂ©veloppement pour prendre en compte les diffĂ©rentes pratiques de gestion des eaux pluviales existantes (noues, toitures vĂ©gĂ©talisĂ©es, ...). Lâutilisation conjointe des donnĂ©es simulĂ©es par les diffĂ©rents modĂšles aidera Ă dĂ©terminer le rĂŽle de la part des surfaces naturelles et artificielles sur les bilans Ă©nergĂ©tique et hydrique en milieu plus ou moins urbanisĂ©. Le milieu pĂ©riurbain Ă©tant en Ă©volution, le projet sâintĂ©ressera aussi Ă des scĂ©narios dâurbanisation prospectifs en regardant dâune part lâimpact de la densification sur les scĂ©narios construits pour lâYzeron lors du projet AVuPUR (ANR-VMCS, 2008-2011) et dâautre part, en rĂ©flĂ©chissant conjointement avec Nantes MĂ©tropole, aux possibles voies dâĂ©volution sur le bassin de la ChĂ©zine
Satellite Sensor Requirements for Monitoring Essential Biodiversity Variables of Coastal Ecosystems
The biodiversity and high productivity of coastal terrestrial and aquatic habitats are the foundation for important benefits to human societies around the world. These globally distributed habitats need frequent and broad systematic assessments, but field surveys only cover a small fraction of these areas. Satellite-based sensors can repeatedly record the visible and near-infrared reflectance spectra that contain the absorption, scattering, and fluorescence signatures of functional phytoplankton groups, colored dissolved matter, and particulate matter near the surface ocean, and of biologically structured habitats (floating and emergent vegetation, benthic habitats like coral, seagrass, and algae). These measures can be incorporated into Essential Biodiversity Variables (EBVs), including the distribution, abundance, and traits of groups of species populations, and used to evaluate habitat fragmentation. However, current and planned satellites are not designed to observe the EBVs that change rapidly with extreme tides, salinity, temperatures, storms, pollution, or physical habitat destruction over scales relevant to human activity. Making these observations requires a new generation of satellite sensors able to sample with these combined characteristics: (1) spatial resolution on the order of 30 to 100-m pixels or smaller; (2) spectral resolution on the order of 5 nm in the visible and 10 nm in the short-wave infrared spectrum (or at least two or more bands at 1,030, 1,240, 1,630, 2,125, and/or 2,260 nm) for atmospheric correction and aquatic and vegetation assessments; (3) radiometric quality with signal to noise ratios (SNR) above 800 (relative to signal levels typical of the open ocean), 14-bit digitization, absolute radiometric calibratio
Satellite sensor requirements for monitoring essential biodiversity variables of coastal ecosystems
© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ecological Applications 28 (2018): 749-760, doi: 10.1002/eap.1682.The biodiversity and high productivity of coastal terrestrial and aquatic habitats are the foundation for important benefits to human societies around the world. These globally distributed habitats need frequent and broad systematic assessments, but field surveys only cover a small fraction of these areas. Satelliteâbased sensors can repeatedly record the visible and nearâinfrared reflectance spectra that contain the absorption, scattering, and fluorescence signatures of functional phytoplankton groups, colored dissolved matter, and particulate matter near the surface ocean, and of biologically structured habitats (floating and emergent vegetation, benthic habitats like coral, seagrass, and algae). These measures can be incorporated into Essential Biodiversity Variables (EBVs), including the distribution, abundance, and traits of groups of species populations, and used to evaluate habitat fragmentation. However, current and planned satellites are not designed to observe the EBVs that change rapidly with extreme tides, salinity, temperatures, storms, pollution, or physical habitat destruction over scales relevant to human activity. Making these observations requires a new generation of satellite sensors able to sample with these combined characteristics: (1) spatial resolution on the order of 30 to 100âm pixels or smaller; (2) spectral resolution on the order of 5 nm in the visible and 10 nm in the shortâwave infrared spectrum (or at least two or more bands at 1,030, 1,240, 1,630, 2,125, and/or 2,260 nm) for atmospheric correction and aquatic and vegetation assessments; (3) radiometric quality with signal to noise ratios (SNR) above 800 (relative to signal levels typical of the open ocean), 14âbit digitization, absolute radiometric calibration <2%, relative calibration of 0.2%, polarization sensitivity <1%, high radiometric stability and linearity, and operations designed to minimize sunglint; and (4) temporal resolution of hours to days. We refer to these combined specifications as H4 imaging. Enabling H4 imaging is vital for the conservation and management of global biodiversity and ecosystem services, including food provisioning and water security. An agile satellite in a 3âd repeat lowâEarth orbit could sample 30âkm swath images of several hundred coastal habitats daily. Nine H4 satellites would provide weekly coverage of global coastal zones. Such satellite constellations are now feasible and are used in various applications.National Center for Ecological Analysis and Synthesis (NCEAS);
National Aeronautics and Space Administration (NASA) Grant Numbers: NNX16AQ34G, NNX14AR62A;
National Ocean Partnership Program;
NOAA US Integrated Ocean Observing System/IOOS Program Office;
Bureau of Ocean and Energy Management Ecosystem Studies program (BOEM) Grant Number: MC15AC0000
Modelisation and Information System Tools to Support the Discovery of Interactive Factors of Vulnerabilities in Life Courses
In the past decades, the life course perspective and the vulnerability framework have grown in popularity to study how risks spread across people lives. Such studies involve complex longitudinal and network data as well as specific analysis methods. This thesis aims to help the social scientist in managing and analyzing such data. To support the provided methodological contributions, the thesis starts by setting a conceptual model of the diffusion of vulnerability along the life course. Then, the thesis develops several complementary strategies for exploring the set of vulnerability descriptive variables with the aim to identify interaction effects, such as when the gender effect depends on the age. The strategies rely on classification trees and specifically focus on unexpected interaction effects and data imbalance. In an illustrative application focusing on vulnerability to poverty, the proposed methods successfully achieved to identify an unexpected interaction effect between ego's and father's educational resources on ego's unemployment. Several of the contributions are made available to the scientific community through a series of R packages
An association rule miner for unbalanced data based on artificial bee colony optimization
Justice ordinaire et justice dâexception sous le Directoire. 1795-1799: Le cas des dĂ©partements belges
- âŠ