A conjugate gradient method for the solution of the non-LTE line radiation transfer problem

This study concerns the fast and accurate solution of the line radiation transfer problem, under non-LTE conditions. We propose and evaluate an alternative iterative scheme to the classical ALI-Jacobi method, and to the more recently proposed Gauss-Seidel and Successive Over-Relaxation (GS/SOR) schemes. Our study is indeed based on the application of a preconditioned bi-conjugate gradient method (BiCG-P). Standard tests, in 1D plane parallel geometry and in the frame of the two-level atom model, with monochromatic scattering, are discussed. Rates of convergence between the previously mentioned iterative schemes are compared, as well as their respective timing properties. The smoothing capability of the BiCG-P method is also demonstrated.Comment: Research note: 4 pages, 5 figures, accepted to A&

A New Metric for Estimating the Disparity of Antenna Patterns in Synthetic Aperture Imaging Radiometry

The soil moisture and ocean salinity (SMOS) satellite has provided for about ten years systematic passive L -band measurements from space. For several months, phase 0 studies are conducted by the French space agency for a second-generation high resolution (HR) follow-on mission. This contribution is making the connection between this SMOS hr project and the SMOS mission by revisiting the following problematic: the impact of the disparity of the antenna patterns on the reconstruction floor error observed in the retrieved brightness temperatures. This impact is revisited in light of the progress made since that time and a new metric is introduced for estimating the disparity between antenna patterns. It would be helpful for the design of future missions based on imaging by aperture synthesis with interferometric arrays comprising a large number of antennas

Non-destructive data assimilation as a tool to diagnose corrosion rate in reinforced concrete structures.

La transcription des symboles et des caractères spéciaux utilisés dans la version originale de ce résumé n’a pas été possible en raison de limitations techniques. La version correcte de ce résumé peut être lue en PDF.Reinforcement corrosion is a major problem in the long-term management of reinforced concrete structures. With sustainability in perspective, knowledge of the corrosion rate (Vcor) makes it possible to estimate the kinetics of the corrosion phenomenon and helps in refining the maintenance strategy of such structures. Although in situ Vcor measurements are possible, data acquisition is time-consuming because of the protocol intrinsic to its measurement (reinforcement polarization made point by point). Therefore, in the context of site diagnostics, these methods cannot reasonably be used systematically on site and must be combined with high performance non-destructive testing (NDT) surface methods (GPR, capacimetry, half-cell corrosion). In addition, depending on the case, Vcor (point measurements) and NDT(surface) data are statistically related. However, there is a lack of efficient data assimilation tools permitting accurate translation of NDT data into pseudo Vcor data. In this paper, we present a numerical tool allowing prediction of Vcor values from NDT measurements. The tool permits application of different data assimilation techniques, i.e., cokriging, Bayesian sequential simulation, and a decision tree-driven learning depending on statistical behavior and available data. The efficiency of our numerical tool has been tested on a dataset acquired on a structure located in the French Alps. Results show that, for the case study, our data assimilation tool allows prediction of Vcor with accuracy compared to in situ measurements and also permits one to infer the uncertainty of the prediction. This opens the door for quantitative use of multiple NDT in the management of reinforced concrete structures.</p

SMOS instrument performance and calibration after six years in orbit

ESA's Soil Moisture and Ocean Salinity (SMOS) mission, launched 2-Nov-2009, has been in orbit for over 6 years, and its Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) in two dimensions keeps working well. The calibration strategy remains overall as established after the commissioning phase, with a few improvements. The data for this whole period has been reprocessed with a new fully polarimetric version of the Level-1 processor which includes a refined calibration schema for the antenna losses. This reprocessing has allowed the assessment of an improved performance benchmark. An overview of the results and the progress achieved in both calibration and image reconstruction is presented in this contribution.Peer ReviewedPostprint (author's final draft

SMOS payload in-orbit performance

Postprint (published version

Développement d’un système d’exploitation pour l’aide au diagnostic des ouvrages du génie civil.

La préservation et la maintenance des ouvrages en béton armé ne peuvent être assurées que par une bonne compréhension de l’état des matériaux et du comportement des structures considérées. À l’échelle d’un ouvrage, la caractérisation de l’état du béton armé nécessite la réalisation de contrôles non destructifs (radar, potentiel électronégatif, capacimétrie, ultrasons, etc.) permettant de cartographier rapidement et en continu la distribution spatiale de différents paramètres physiques intrinsèquement liés aux pathologies en cours de développement. Ces cartographies permettent d’implanter judicieusement les prélèvements indispensables à la réalisation d’analyses en laboratoire (essais physique, chimique, microstructure). Dans l’optique d’une approche performantielle, le monitorage de différents paramètres structurels (roulis, basculement, ouverture de fissures, etc.) et environnementaux (température, hygrométrie, etc.) doit également être réalisé afin de déterminer le comportement de l’ouvrage au cours du temps et d’évaluer sa durabilité. Les gestionnaires d’ouvrages et les ingénieurs chargés des études se trouvent ainsi confrontés à devoir gérer d’importants volumes de données multi-échelles et multivariées évoluant dans l’espace et le temps. La gestion, la compilation et la valorisation de ces données représentent actuellement un travail fastidieux, redondant, extrêmement chronophage, pouvant mener à des erreurs d’appréciation et d’interprétation et donc à des diagnostics erronés. Pour fiabiliser les diagnostics, il est crucial d’intégrer ces données entre elles de manière intelligible, claire et cohérente dans le but d’offrir aux gestionnaires d’ouvrages un outil pertinent d’aide à la décision basé sur des éléments factuels (identification et caractérisation des hétérogénéités, répartition de l'humidité, potentiel de corrosion, vitesse de corrosion, indicateurs de risque, simulation, prédiction, etc.). Dans cette optique, un nouveau système d’exploitation de données a été développé. Ce système, nommé Datae, repose notamment sur l'utilisation de techniques d'imagerie 3D et de méthodes innovantes d'intégration des données qui augmentent considérablement leur représentativité et leur exploitation dans l'espace et le temps. Datae permet à la fois d’exploiter des flux de données diversifiés, de représenter ces données de façon claire, de réaliser des simulations et d’aider les gestionnaires d’ouvrages à anticiper l’évolution des pathologies des infrastructures de manière à optimiser les travaux de maintenance. Cette optimisation a pour but de limiter les pertes d’exploitation des infrastructures, bénéfice important pour les gestionnaires d’ouvrages. The preservation and maintenance of reinforced concrete structures can only be ensured by a good understanding of the state of the materials and the behavior of the considered structures. At the scale of a structure, the characterization of the state of the reinforced concrete requires the realization of non-destructive tests (radar, electronegative potential, capacimetry, ultrasound, etc.) allowing to map rapidly and continuously the spatial distribution of different physical parameters intrinsically related to pathologies under development. These maps make it possible to judiciously collect samples required for laboratory analyzes (physical, chemical, microstructure tests). In the context of a performance-based approach, the monitoring of various structural parameters (roll, tilt, crack opening, etc.) and environmental parameters (temperature, hygrometry, etc.) must also be performed in order to determine the behavior of the work over time and evaluate its durability. The book managers and the engineers in charge of the studies are thus confronted with having to manage large volumes of multi-scale and multivariate data evolving in space and time. The management, the compilation and the utilization of these data represent a tedious work, redundant, extremely time consuming, which can lead to errors of appreciation and interpretation and thus erroneous diagnoses. To make diagnostics more reliable, it is crucial to integrate these data in an intelligible, clear, and consistent manner in order to provide resource managers with a relevant evidence-based decision support tool (identification and characterization of heterogeneities, moisture distribution, corrosion potential, corrosion rate, risk indicators, simulation, prediction, etc.). With this in mind, a new data operating system has been developed. This system, called Datae, is based in particular on the use of 3D imaging techniques and innovative data integration methods that considerably increase the representativeness and the exploitation of the data, both in space and time. Datae allows exploiting diversified data flows, representing these data in a clear way, performing simulations, and helps project owners anticipating the evolution of infrastructure pathologies in order to optimize the work of maintenance. This optimization aims to limit infrastructure operating losses, a major benefit for building owners

Stabilized image reconstruction algorithm for Synthetic Aperture Imaging Radiometers.

Synthetic Aperture Imaging Radiometers (SAIR) promise to be powerful sensors for high-resolution observations of the Earth at low microwaves frequencies. The SMOS (Soil Moisture and Ocean Salinity) space mission is an ESA (European Space Agency) led project aimed at global monitoring of surface soil moisture and sea surface salinity from L-band space borne observations. It will be the first attempt to apply to remote sensing of the Earth surface, the concept of imaging interferometric radiometry by aperture synthesis, initially developed for radio astronomy. Interferometer measurements, also called complex visibilities, are obtained by cross-correlating the signals collected by pairs of spatially separated antennae which have overlapping fields of view. Visibility samples are related to the radiometric brightness temperature of the observed scene by a spatial Fourier-like integral. However, due to the angular extent of the target, the conditions, which typically apply for radio astronomy observations, are no longer valid for Earth remote sensing. As a consequence, the standard imaging algorithms developed by radio astronomers are not convenient for retrieving brightness temperatures of the scene from complex visibilities. The finite physical size of a synthetic antenna results in a truncation of the visibility samples above a certain spatial frequency. The Y-shaped array, filled with equally spaced elements, selected for SMOS leads to complex visibilities sampled over a hexagonal grid inside a star-shaped window in the Fourier domain. The relationship between complex visibility samples and radiometric brightness temperature can thus be rephrased in the Fourier domain: the unknowns are the Fourier components of the scene brightness temperature. Thanks to spatial redundancies, the number of these Fourier components inside the star-shaped window is smaller than the number of visibility samples: the over-determined inverse problem has to be solved in the least-squares sense. This contribution extends the concept of "resolvant matrix" to the case of remote sensing of the Earth at low microwaves frequencies. The stability of the reconstruction process is studied in depth, including the influence of the modeling of the instrument on the propagation of errors. To support the theory and to illustrate the performances of this imaging method, in terms of accuracy and computational time, numerical simulations are presented within the frame of the SMOS project

Amplitude and Phase Calibration with the Aid of Beacons in Microwave Imaging Radiometry by Aperture Synthesis: Algebraic Aspects and Algorithmic Implications

In remote sensing via aperture synthesis, the complex gains of every elementary antenna have to be very well known for measuring accurate complex visibilities. The role of calibration is to estimate the instrumental and environmental variations that may affect interferometric measurements. This contribution focuses on the calibration of the effective transfer function of aperture synthesis radiometers with the aid of a radio beacon, in the same way radio-astronomers use quasi-stellar radio sources to calibrate that of radio-telescope arrays. If the amplitude calibration of complex gains does not raise any issue, it is shown that phase calibration may bring up serious challenges if it is not given special attention. Indeed, the phase of the complex visibilities cannot be roughly unwrapped as the risk of a wrong estimation of the complex gains is real and proven. This problem is overcome with the aid of a non-linear optimization algorithm for iteratively and smoothly unwrapping these phases. The performances of both amplitude and phase calibration are then assessed by means of numerical simulations with emphasis on the sensitivity of the accuracy to the inversion method as well as to various errors

Caractérisation géophysique de la structure interne d'une halde à stériles

Méthodes de caractérisation géophysique -- Méthode électrique -- Méthodes électromagnétiques -- Performances théoriques des différentes méthodes utilisées -- Présentation du site et études antérieures -- Mesures géophysique de terrain -- Dispositifs d'acquisition utilisés -- Implantation des profils géophysiques et paramètres d'acquisition associés -- Résultats et interprétation -- Surface du banc supérieur de la halde -- Pente -- Levés en forages -- Analyse et discussion des résultats -- Analyse et modèle structural proposé