Bayesian segmentation of hyperspectral images

In this paper we consider the problem of joint segmentation of hyperspectral images in the Bayesian framework. The proposed approach is based on a Hidden Markov Modeling (HMM) of the images with common segmentation, or equivalently with common hidden classification label variables which is modeled by a Potts Markov Random Field. We introduce an appropriate Markov Chain Monte Carlo (MCMC) algorithm to implement the method and show some simulation results.Comment: 8 pages, 2 figures, presented at MaxEnt 2004, Inst. Max Planck, Garching, German

Gradient Scan Gibbs Sampler: an efficient algorithm for high-dimensional Gaussian distributions

This paper deals with Gibbs samplers that include high dimensional conditional Gaussian distributions. It proposes an efficient algorithm that avoids the high dimensional Gaussian sampling and relies on a random excursion along a small set of directions. The algorithm is proved to converge, i.e. the drawn samples are asymptotically distributed according to the target distribution. Our main motivation is in inverse problems related to general linear observation models and their solution in a hierarchical Bayesian framework implemented through sampling algorithms. It finds direct applications in semi-blind/unsupervised methods as well as in some non-Gaussian methods. The paper provides an illustration focused on the unsupervised estimation for super-resolution methods.Comment: 18 page

Sampling high-dimensional Gaussian distributions for general linear inverse problems

International audienceThis paper is devoted to the problem of sampling Gaussian distributions in high dimension. Solutions exist for two specific structures of inverse covariance: sparse and circulant. The proposed algorithm is valid in a more general case especially as it emerges in linear inverse problems as well as in some hierarchical or latent Gaussian models. It relies on a perturbation-optimization principle: adequate stochastic perturbation of a criterion and optimization of the perturbed criterion. It is proved that the criterion optimizer is a sample of the target distribution. The main motivation is in inverse problems related to general (non-convolutive) linear observation models and their solution in a Bayesian framework implemented through sampling algorithms when existing samplers are infeasible. It finds a direct application in myopic,unsupervised inversion methods as well as in some non-Gaussian inversion methods. An illustration focused on hyperparameter estimation for super-resolution method shows the interest and the feasibility of the proposed algorithm

Correlation between homogeneous propane pyrolysis and pyrocarbon deposition

International audiencePyrocarbon deposition through propane pyrolysis is studied in a 1-D hot-wall CVD furnace. The gas-phase pyrolysis is modelled with a partially reduced kinetic mechanism leading to polycyclic aromatic compounds (PAHs). The C2-C4 and C3 reaction paths are in competition for benzene formation. There is also an independent C3-C5 path leading to naphthalene. The gas-phase concentrations are correlated with experimental data including in-situ FTIR spectra intensities, pyro- carbon deposition rates, and pyrocarbon nanotextures. Rough Laminar pyrocarbon deposition appears to be more related to PAHs than Smooth Laminar pyrocarbon

Kinetic modeling of gas-phase decomposition of propane : correlation with pyrocarbon deposition

International audienceA chemical kinetic model for gas-phase pyrolysis of propane has been set up, partially reduced, and validated against FTIR measurements in a tubular hot-wall reactor at P = 2 kPa, and T = 900 to 1400 K. It confirms the notion of "maturation" from propane to lighter hydrocarbons, the to aromatic compounds and PAHs. The gas-phase composition above the substrate has been correlated to pyrocarbon deposition rates and to the deposit nanostructure. It is confirmed that the growth of the rough laminar (RL) form would be related to heavier gaseous species than for the smooth laminar (SL) form

CVD/CVI du pyrocarbone : analyse in situ de la phase gazeuse ; études cinétique et structurale

As part of the determination of the mechanisms of chemical vapor deposition of laminar pyrocarbons, an experimental study was conducted. This includes (i) the analysis of the composition of the gas phase (by in-situ Fourier transform infrared spectrometry and mass spectrometry), (ii) the in-situ kinetic study of pyrocarbon formation (microbalance) and (iii) analysis of the structure of the deposited carbon (polarized light optical microscopy and transmission electron microscopy). The experimental parameters studied are temperature and residence time, in order to highlight the effect of the advancement of homogeneous reactions (maturation) on the rate of deposition and on the structure of carbon. The experiments mainly concern the deposition (CVD) in the case of propane pyrolysis. However, other gaseous systems (benzene, methane/carbon tetrachloride) were also examined and infiltration aspects (CVI) were taken into account. The correlations that are established in particular between the kinetic and structural studies carried out with the precursor propane, have led to the proposal of a qualitative model that explains the transitions between kinetic regimes and between microtextural types by the existence of two parallel pathways for the formation of laminar pyrocarbon. These two modes of deposition would involve two different families of gaseous species and would lead to the formation of the two types of pyrocarbon most frequently encountered in CVI, namely the so-called smooth laminar and rough laminar carbons.Dans le cadre de la détermination des mécanismes du dépôt chimique en phase vapeur des pyrocarbones laminaires, une étude expérimentale a été conduite. Celle-ci comprend (i) l'analyse de la composition de la phase gazeuse (par spectrométrie infrarouge à transformée de Fourier in-situ et par spectrométrie de masse), (ii) l'étude cinétique in-situ de la formation du pyrocarbone (microbalance) et (iii) l'analyse de la structure du carbone déposé (microscopie optique en lumière polarisée et microscopie électronique en transmission). Les paramètres expérimentaux étudiés sont la température et le temps de séjour, afin de mettre en évidence l'effet de l'avancement des réactions homogènes (maturation) sur la vitesse de dépôt et sur la structure du carbone. Les expérimentations concernent essentiellement le dépôt (CVD) dans le cas de la pyrolyse du propane. Cependant d'autres systèmes gazeux (benzène, méthane / tetrachlorure de carbone) ont également été examinés et les aspects liés à l'infiltration (CVI) ont été pris en compte. Les corrélations qui s'établissent notamment entre les études cinétique et structurale réalisées avec le précurseur propane, ont conduit à la proposition d'un modèle qualitatif qui explique les transitions entre régimes cinétiques et entre types microtexturaux par l'existence de deux voies parallèles pour la formation du pyrocarbone laminaire. Ces deux modes de dépôt impliqueraient deux familles d'espèces gazeuses différentes et mèneraient à la formation des deux types de pyrocarbone les plus fréquemment rencontrés en CVI, à savoir les carbones dits laminaire lisse et laminaire rugueux

CVD/CVI du pyrocarbone : analyse in situ de la phase gazeuse ; études cinétique et structurale

As part of the determination of the mechanisms of chemical vapor deposition of laminar pyrocarbons, an experimental study was conducted. This includes (i) the analysis of the composition of the gas phase (by in-situ Fourier transform infrared spectrometry and mass spectrometry), (ii) the in-situ kinetic study of pyrocarbon formation (microbalance) and (iii) analysis of the structure of the deposited carbon (polarized light optical microscopy and transmission electron microscopy). The experimental parameters studied are temperature and residence time, in order to highlight the effect of the advancement of homogeneous reactions (maturation) on the rate of deposition and on the structure of carbon. The experiments mainly concern the deposition (CVD) in the case of propane pyrolysis. However, other gaseous systems (benzene, methane/carbon tetrachloride) were also examined and infiltration aspects (CVI) were taken into account. The correlations that are established in particular between the kinetic and structural studies carried out with the precursor propane, have led to the proposal of a qualitative model that explains the transitions between kinetic regimes and between microtextural types by the existence of two parallel pathways for the formation of laminar pyrocarbon. These two modes of deposition would involve two different families of gaseous species and would lead to the formation of the two types of pyrocarbon most frequently encountered in CVI, namely the so-called smooth laminar and rough laminar carbons.Dans le cadre de la détermination des mécanismes du dépôt chimique en phase vapeur des pyrocarbones laminaires, une étude expérimentale a été conduite. Celle-ci comprend (i) l'analyse de la composition de la phase gazeuse (par spectrométrie infrarouge à transformée de Fourier in-situ et par spectrométrie de masse), (ii) l'étude cinétique in-situ de la formation du pyrocarbone (microbalance) et (iii) l'analyse de la structure du carbone déposé (microscopie optique en lumière polarisée et microscopie électronique en transmission). Les paramètres expérimentaux étudiés sont la température et le temps de séjour, afin de mettre en évidence l'effet de l'avancement des réactions homogènes (maturation) sur la vitesse de dépôt et sur la structure du carbone. Les expérimentations concernent essentiellement le dépôt (CVD) dans le cas de la pyrolyse du propane. Cependant d'autres systèmes gazeux (benzène, méthane / tetrachlorure de carbone) ont également été examinés et les aspects liés à l'infiltration (CVI) ont été pris en compte. Les corrélations qui s'établissent notamment entre les études cinétique et structurale réalisées avec le précurseur propane, ont conduit à la proposition d'un modèle qualitatif qui explique les transitions entre régimes cinétiques et entre types microtexturaux par l'existence de deux voies parallèles pour la formation du pyrocarbone laminaire. Ces deux modes de dépôt impliqueraient deux familles d'espèces gazeuses différentes et mèneraient à la formation des deux types de pyrocarbone les plus fréquemment rencontrés en CVI, à savoir les carbones dits laminaire lisse et laminaire rugueux