Caractérisation de films d'huile de la bande X à la bande K, expérimentation en bassin à vagues

This paper depicts an experiment conducted in a wind-wave pool in Brest, France, to characterize oil films when observed at moderate incidence from a X-to-K-band radar. Simultaneous measurements of surface elevation and radar backscattered field were carried out for various sea water surface states and incident angles. From this meaningful dataset (mainly lying in simultaneous acquisitions in X-, Ku-and K-band), an inversion method is proposed to characterize some properties of the oil film: its origin (mineral or biogenic) and its fractional coverage indicator. This process is based on the minimization of the cost function correlating the values given by a physical model of the wave damping ratio and the measured ones. The resulting oil parameters are found in overall good agreement with the three different released oils (two mineral and one biogenic) and it is observed that the fractional filling indicator of the oil slick decreases with increasing the roughness surface state whatever the considered oil.Ce papier décrit une expérimentation menée dans un bassin à vagues à Brest, France. L'objectif est de caractériser les films d'huile observés au moyen d'un système radar à des angles d'incidence modérée de la bande X à la bande K. Des mesures simultanées de l'élévation de la surface et du champ électromagnétique rétro-diffusé furent réalisées pour différents états de surface et divers angles d'incidence. A partir de cette base de données, une méthode d'inversion est proposée pour caractériser plusieurs propriétés du film d'huile: son origine (minérale ou biogénique) ainsi que sa fraction de couverture surfacique. Ce processus repose sur la minimisation d'une fonction coût liant la modélisation physique du coefficient d'atténuation des vagues avec la mesure. Les paramètres estimés sont en accord avec les trois huiles différentes déversées (deux minérales et une biogénique). Il est également observé que la fraction de couverture surfacique de la nappe d'huile décroît avec l'augmentation de la rugosité de surface et ce, quelle que soit l'huile considérée

Sensibilité des observables radars à la variabilité temporelle et à la configuration géométrique de forêts tempérées et tropicales à partir de mesure de proximité haute-résolution

L'augmentation importante de la population mondiale, et par conséquent de ses besoins, exerce une pression de plus en plus importante sur les surfaces forestières. L'outil le mieux adapté au suivi des forêts, à l'échelle du globe, est la télédétection. C'est dans ce contexte que se situe ce travail de thèse, qui vise à améliorer l'estimation des paramètres biophysiques des arbres à partir de données de télédétection. L'originalité de ce travail a été d'étudier cette estimation des paramètres biophysiques en menant plusieurs études de sensibilité avec une démarche expérimentale sur des données expérimentales et sur des données simulées. Tout d'abord, l'étude s'est portée sur des séries temporelles de mesures de diffusiométrie radar obtenues sur deux sites : l'un constitué d'un cèdre en zone tempérée et l'autre d'une parcelle de forêt tropicale. Puis, cette étude de sensibilité a été poursuivie en imageant, avec une résolution élevée, plusieurs parcelles aux configurations différentes à l'intérieur d'une forêt de pin. Enfin, des données optiques et radars simulées ont été fusionnés afin d'évaluer l'apport de la fusion de données optique et radar dans l'inversion des paramètres biophysiques.The significant increase of the world population, and therefore its needs, pushes increasingly high in forest areas. The best tool for monitoring forest across the globe is remote sensing. It is in this context that this thesis, which aims to improve the retrieval of biophysical parameters of trees from remote sensing data, takes place. The originality of this work was to study the estimation of biophysical parameters across multiple sensitivity studies on experimental data and simulated data. First, the study focused on the time series of radar scatterometry measurements obtained on two sites: one characterized by a cedar in the temperate zone and the other by a forest plot of rainforest. Then, the sensitivity analysis was continued by imaging with high resolution, several forest plots with different configurations within a pine forest. Finally, simulated radar and optical data were combined to evaluate the contribution of optical and radar data fusion in the inversion of biophysical parameters.RENNES1-Bibl. électronique (352382106) / SudocSudocFranceF

On the use of rigorous microwave interaction models to support remote sensing of natural surfaces

A study has been undertaken which objective is to contribute to the investigation of the validity of microwave surface scattering models used in remote sensing applications, particularly when applied to realistic representations of natural surfaces. These investigations are based on recent implementations of rigorous methods (MoM and FDTD) and cover a wide range of configurations of observation (mono- and bi-static). Both land (bare soils) and sea surfaces are being investigated

Characterization of a cinnamoyl-CoA reductase 1 (CCR1) mutant in maize: effects on lignification, fibre development, and global gene expression

Cinnamoyl-CoA reductase (CCR), which catalyses the first committed step of the lignin-specific branch of monolignol biosynthesis, has been extensively characterized in dicot species, but few data are available in monocots. By screening a Mu insertional mutant collection in maize, a mutant in the CCR1 gene was isolated named Zmccr1–. In this mutant, CCR1 gene expression is reduced to 31% of the residual wild-type level. Zmccr1– exhibited enhanced digestibility without compromising plant growth and development. Lignin analysis revealed a slight decrease in lignin content and significant changes in lignin structure. p-Hydroxyphenyl units were strongly decreased and the syringyl/guaiacyl ratio was slightly increased. At the cellular level, alterations in lignin deposition were mainly observed in the walls of the sclerenchymatic fibre cells surrounding the vascular bundles. These cell walls showed little to no staining with phloroglucinol. These histochemical changes were accompanied by an increase in sclerenchyma surface area and an alteration in cell shape. In keeping with this cell type-specific phenotype, transcriptomics performed at an early stage of plant development revealed the down-regulation of genes specifically associated with fibre wall formation. To the present authors’ knowledge, this is the first functional characterization of CCR1 in a grass species

Une méthode de sous-domaines pour la résolution des équations de Maxwell instationnaires en présence d'un ensemble non-connexe d'objets diffractant

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Corrigendum to ``Test particle motion around an oblate planet'' [Icarus 107 (1994) 129 141]

International audienceNot Availabl

Homogenization Techniques for Improving the Calculations of Scattering by 1-D Fast Oscillating Periodic Surfaces

International audienceThis paper deals with the efficient computation of scattering problems by fast oscillating periodic surfaces using two-scale expansion homogenization techniques. The proposed method splits the field between an effective field and a boundary layer corrector and applies an asymptotic expansion. Then, the evaluation of these boundary layers leads to the extraction of effective parameters, modeling the effects of the highly oscillating surface on the scattered field. A previous paper has already presented such a technique to deal with TM polarization. First, this paper extends the approach to TE polarization and completes it by pointing out all the key points. Especially it shows the map of the split fields underlining the physical contribution of each term. Second, this paper exposes and compares two different uses of these computed effective parameters. Numerical examples show the validity of the method, especially by justifying the asymptotic expansion ansatz. Computational efficiency is discussed

Measure of Temporal Variation of P-Band Radar Cross Section and Temporal Coherence of a Temperate Tree.

International audienceThis paper deals with a ground experiment based on a P-band scatterometer that measured the evolution of the radar cross section (RCS) and coherence of a temperate tree in HV polarization, during four periods spread over nine months, over a cedar tree. Watering of the tree has limited influence in time on the RCS, i.e., limited to around 30 min, but impacts the coherence over a longer period of time. Analysis of the series shows that according to the season considered, clear daily cycles from 1 to 2 dB may appear on the coherence only (autumn) or on both coherence and RCS (spring), whereas in winter, they are absent on both results. It was analyzed in the literature that the variations in RCS are strongly correlated to the variations in the dielectric constant in trunks and branches. In addition, it was shown that the HV RCS presents seasonal trends with a yearly cycle of roughly 3 dB following similar trends reported for trunk moisture content time series