Développement de méthodes de mesure de l'émissivité et de l'indice optique de solides opaques homogènes

Nous avons d'abord étudié diverses méthodes de mesure de l'émissivité. Nous avons effectuées des mesures en réflectométrie spectrale bidirectionelle sur différents matériaux à température ambiante et des mesures en émission directe sur des revêtements à très basse température (en totale de 40 K à l'ambiante et de 1 à 1000 m et en spectrale de 250K à l'ambiante et de 20 à 120 m). Nous avons ensuite étudié l'influence du changement de phase alpha gamma dans des alliages de Fer-Nickel sur l'indice optique. A partir de mesures d'émissivité spectrale directionelle à différentes températures proche de 500C pour différents échantillons ayant différentes concentrations de Fe-Ni, nous avons restitué par des méthodes numériques d'optimisation le spectre de l'indice optique aux différentes températures de 2 à 12 m.We initially studied various methods of measurement of emissivity. We took measurements in bidirectional spectral reflectometry on various materials at ambient temperature and measurements in direct emission on coatings at very low temperature (in total from 40K to ambient and from 1 to 1000 m and in spectral from 250K to ambient and from 20 to 120 m). We then studied the influence of the phase shift alpha gamma in Iron-nickel alloys on the optical index. From measurements of directional spectral emittance at various temperatures near 500C for various samples having various Fe-Ni concentrations, we restored by numerical methods of optimization the spectrum of the optical index at the various temperatures from 2 to 12 m.NANTERRE-BU PARIS10 (920502102) / SudocSudocFranceF

A symptom network analysis of exercise addiction and personality on ultra-marathon runners with serious complications

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Direct measurement of total emissivities at cryogenic temperatures: Application to satellite coatings

International audienceThis paper presents a direct measurement method for optical properties of different materials at cryogenic temperatures from 20 K to 200 K. It has been developed within the framework of the design of Planck program. Planck is a satellite of the European Space Agency (ESA) that will be launched in 2008. The scientific goal of the Planck mission is to make observations of the temperature anisotropy and polarisation of the Cosmic Microwave Background. The equivalent temperature of the observed radiation is about 3 K and the telescope baffle temperature should not exceed 60 K in order to work properly. The large Planck telescope is passively cooled by radiating to the Deep Space, so that a good knowledge of the thermo-optical properties of its coating is of utmost importance for thermal modelling. However, up to now, few measurements have been done at such low temperatures. We derived a direct measurement method for the total directional emissivity of various coatings of interest for satellites applications. The effective spectral range chosen the measurements covers 6–800 μm. We will describe the design of the measurement apparatus and present results for several coatings

Internal structure and permafrost distribution in two alpine periglacial talus slopes, Valais, Swiss Alps

In order to determine the spatial extension and the characteristics of permafrost within alpine talus slopes, two sites located in the western part of the Swiss Alps were studied using borehole drilling and electrical resistivity tomography (ERT) profiles. Three boreholes were drilled along an upslope–downslope transect in both talus slopes. In both sites, frozen sediments are present only in the two lowest boreholes, whereas the upper borehole does not present ice. This stratigraphy is confirmed by ground temperatures registered in the boreholes. In each site, three upslope–downslope ERT profiles were crossed with five, respectively four horizontal ERT profiles. All the upslope–downslope profiles show a difference in resistivities between the upper and lower parts of the slope, where a large resistive body with values higher than 35 kΩm is present. In the uppermost part of the profiles, the resistivities are lower than 10–15 kΩm. The borehole data allowed the stratigraphy obtained from the ERT inverted profiles to be validated, with regards to the distribution of frozen sediments as well as the depth of the detected structures. The results confirm that, in the two studied sites, permafrost is present in the lower sections of the talus slopes, whereas it is absent in the upper parts. Finally, the analysis of the talus structure showed that the permafrost stratigraphy, and in particular the ice content, may be an important element of interpretation of the palaeoclimatic significance of an alpine talus slope

Combination at the Observation Level: contribution to ITRF2013

International audienceThe new ITRF2013 realization is planned to rely on single-technique combined solutions. However, other solutions based on combination of techniques at the observation level will be evaluated. Since several years, such a project has been developed by the GRGS (Groupe de Recherche en Géodésie Spatiale). Its main objective is to search for an optimal strategy to combine observations and normal equations derived from the processing of the whole set of different space geodetic observations (GPS, DORIS, LLR, SLR and VLBI), this for estimating astro-geodetic parameters (Station positions, Earth Orientation Parameters (EOP), quasar coordinates). Other parameters, such as zenithal troposphere delay, orbit parameters will be determined as well. In the first step, observations are processed by a unique software (GINS) complying with the IERS Conventions, constants and models for insuring homogeneity and consistency. The second step consists in identifying the systematic errors and mitigating their effects, such as inconsistencies of the a priori individual networks, aliasing in sub-daily EOP and no net rotation of the ensemble of quasar coordinates. The ensemble of weekly unconstrained normal equations covering a period of 10 years will be produced and made available for analysis

Combination at the Observation Level:contribution to ITRF2013

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Multi Technique Combination for Earth Orientation Parameters, station and quasar coordinates

International audienceThe GRGS (Groupe de Recherche en Géodésie Spatiale) has developed a new approach to estimate geodetic parameters such as Earth Orientation Parameters (EOP), quasar coordinates for celestial frame (CRF) and station coordinates for terrestrial frame (TRF) in a global procedure. This strategy consists to combine normal equations derived from observations processed by several geodetic techniques (GPS, DORIS, LLR, SLR, VLBI) using a unique software (GINS) complying with IERS Conventions, constants and models for insuring homogeneity and consistency. This combination benefits of the advantages of each technique and the links between them using the common parameters such as EOP and zenithal tropospheric parameters. We present the processing used and the solutions obtained over one year as a preliminary solution such as EOP compared to the IERS C04 series, station coordinates compared to the terrestrial frame ITRF2008 and quasars coordinates compared to the celestial reference frame ICRF2

Multi Technique Combination for Earth Orientation Parameters, station and quasar coordinates

The GRGS (Groupe de Recherche en Géodésie Spatiale) has developed a new approach to estimate geodetic parameters such as Earth Orientation Parameters (EOP), quasar coordinates for celestial frame (CRF) and station coordinates for terrestrial frame (TRF) in a global procedure. This strategy consists to combine normal equations derived from observations processed by several geodetic techniques (GPS, DORIS, LLR, SLR, VLBI) using a unique software (GINS) complying with IERS Conventions, constants and models for insuring homogeneity and consistency. This combination benefits of the advantages of each technique and the links between them using the common parameters such as EOP and zenithal tropospheric parameters. We present the processing used and the solutions obtained over one year as a preliminary solution such as EOP compared to the IERS C04 series, station coordinates compared to the terrestrial frame ITRF2008 and quasars coordinates compared to the celestial reference frame ICRF2