arXiv subjects

François Demontoux

Publications and source records attributed to François Demontoux.

12 recordsLinked to original sources

arXiv2009

Modelisation Des Effets De la Rugosite Sur L'Etude De L'Humidite Des Sols Par Radiometrie Micro-Ondes. Application a la Mission Spatiale Smos

As part of the SMOS mission (Soil Moisture and Ocean Salinity) IMS and EPHYSE laboratories are involved in the study and validation of the inversion algorithm LMEB. In the framework of this study, we developed a model using the numerical modeling software-HFSS ANSOFT. It allows the computation of the emissivity of multilayer systems (soil-litter for example). We have improved our approach to incorporate new parameters that can have a significant effect on the measurements. Indeed, so far the effect of soil roughness associated with the litter has not been studied. Moreover, the thickness of litter is never constant and we must therefore introduce a realistic profile of litter thickness. This article presents our work to integrate these profiles in our numerical model. These profiles may be derived from measurements (litter thickness profiles or soil roughness profiles) or calculations (roughness profile). In both cases the input data of our model are files of XYZ points representing our profile.

physics.geo-ph↗

arXiv2009

Caracterisation Electromagnetique in-Situ De Sols En Bande L. Application a L'Identification De Profils Geologiques

The development of instruments for remote sensing applications (active or passive) requires in situ validation measurements. The equipments (radar or radiometer) must be tested on real geological profiles. We must have accurate information on the profiles studied (permittivity, humidity, thickness of layers ...). Sensors (humidity), samples (thickness) or laboratory measurements (permittivity) provide local data about the profile while the remote sensing equipment is performing global measurements on a geological structure. The present work describes an in situ characterization bench test, based on two horn antennas, associated with an identification profiles software we developed to obtain comprehensive and instantaneous information on the geological profiles.

physics.geo-ph↗

arXiv2008

Modélisation de la propagation dans une structure fermée surdimensionnée

The propagation of an electromagnetic wave in closed structures led to numerous applications ranging from the characterization of materials in resonating cavities to the measurements using pregnant reverberant EMF. We created models to study the existence of electromagnetic waves in large closed structures. There are two ways of excitation in such structures. One of these methods is based on continuous excitation with specific resonant modes, which has a variety of applications. The second method consists of a pulsed excitation similar to the impulse wave radar. This excitation provides other information. The structures studied were closed by perfectly conducting walls and the electromagnetic wave was generated in the structure using dipole antennas. The dimensions (length, width and height) were always much larger than the wavelength.

physics.class-ph↗

arXiv2008

Amélioration de l'étude de l'étude de l'humidité de sols par radiométrie. Caractérisation et modélisation diélectriques de profils géologiques

The surface soil moisture is a key variable to describe the exchange of water and energy between the land and the atmosphere. In hydrology, and meteorology, the amount of water in the upper soil layers permits (0-5 cm from the surface) the evaluation of the relationship between the real evaporation and the potential evaporation of the bare soil. It is also possible to determine the distribution of rainfall or other variables such as hydraulic conductivity. Studies have shown that microwave sensors could be used to scan the surface soil moisture. The solution choose by the team associated with the SMOS mission (Soil Moisture and Ocean Salinity) is to use a radiometer (1.4 GHz) to identify soil microwave emissions . The measurements are made on the site of CESBIO in Toulouse where a 1.4 GHz radiometer is installed . The effect of vegetation cover, soil temperatures, snow cover, topography or moisture variations have an important role in the broadcast microwave surface. Other parameters such as the presence of inclusions in the ground (holes, stones), or soil texture can also disrupt measurements. The aim of the work that we present in this paper is to develop a numerical model to simulate complex geological structures. This model must take into account all parameters that can affect the equivalent permittivity measured by the radiometer (surface, moisture variation ,... inclusions). The purpose of this model is to calculate the equivalent permittivity of these geological structures in order to be able to associate with each radiometer measurement an equivalent moisture.

physics.geo-ph↗

arXiv2007

Approche pédagogique sur l'innocuité des technologies de réseaux sans fil

The wireless networks technologies are becoming more prevalent. As part of our courses, we have to deal with the technical aspects of these technologies. However, the experience of mobile telephony has shown fears that these products can lead to the general public. The latter comes from the use of electromagnetic waves at frequencies close to the frequencies of microwaves oven(2.45 GHz). Studies are under way for years in order to identify the possible effects on the body related to prolonged use of mobile phones. Wireless networks like WiFi or ZigBee for example works with microwave frequencies. On the other hand, problems relating to electromagnetic compatibility waves with the electronic devices must also be studied. The question of the safety of these technologies must be addressed with the students. They will may need to install such equipment. We have integrated the teaching of wireless networks in a chapter dealing with current standards of exposure to electromagnetic waves for living beings and the electronic devices. The aim of our approach is the obtention of knowledges by the student. so he will be able to form an opinion and to provide a speech enlightened to future users of these networks. To this end, we have developed a visualization tool for the distribution of electromagnetic fields. This tool being used will help you understand the electromagnetic environment in which we live and quantify the values of electromagnetic fields (telephony, television, radio, WiFi, Bluetooth, ZigBee, microwave oven, etc.).

physics.ed-ph↗

arXiv2007

Caractérisation électromagnétique de milieux hétérogènes naturels - Application à la mesure de l'humidité du sol par radiométrie micro-onde

The work which we present takes place within the framework of mission SMOS of the ESA which will consist to send a radiometer (1.4 GHz) in space. The goal of the research which we propose is the improvement of the comprehension of the effects of structure soil and litter. The effects of the litter and heterogeneities of the ground are probably important but still are very ignored. So we developed an experimental approach in laboratory and in situ. That makes it possible to take measurements for various configurations (frequency, temporal, polarization, incidence, Bi-statics, Brewster effect...) and in term of surface conditions(homogeneous or heterogeneous ground, more or less wet, presence of litter...). Measurements at the laboratory with waveguide enabled us to characterize the various components of the geological structure (ground, rocks) and to check the model of Dobson usually used.

physics.geo-ph↗

arXiv2007

Caracterisation Electromagnetique De Materiaux Geologiques En Vue Du Suivi De L'Humidite Des Sols Par Radiometrie Micro-Ondes

The work which we present takes place within the framework of mission SMOS of the ESA which will consist to send a radiometer (1.4 GHz) in space. The goal of the research which we propose is the improvement of the comprehension of the effects of structures composed of soil and litter. The effects of the litter and heterogeneities of the ground are probably important but still ignored. The objective of this work was to study the dielectric properties of a type of litter and ground in order to integrate these values into an analytical multi layers model of soil. The objective is to characterize the effects of this layer on the total multi layer system. This will make possible to lead to a simple analytical formulation of a model of litter which can be integrated into the calculation algorithm of SMOS in order to collect information on moisture starting from measurements of emissivity

physics.geo-ph↗

arXiv2007

Etude D'Un Modele D'Inversion Liant L'Emissivite a L'Humidite Des Sols. Contribution a la Mise Au Point De L'Algorithme De la Mission Smos

The work which we present takes place within the framework of mission SMOS of the ESA which will consist to send a radiometer (1.4 GHz) in space. The goal of the research which we propose is the improvement of the comprehension of the effects of structure soil and litter. The effects of the litter and heterogeneities of the ground are probably important but still ignored. Its effect can be corrected via a simple radiative model. It is thus necessary to set up an analytical model which would make it possible to correct the effect of this additional layer. The objective of this article is to present the analytical models which we retained to correct the effect of the vegetation and the litter in order to know the emissivity of the bare soil. We developed a numerical model (with software HFSS) of calculation of the emissivity of multi-layer systems in order to validate the results of the forward inversion models. Ranges of permittivity are introduced with the model in order to take account of the disturbances related to measurement and the variation of the water content of the layers.

physics.geo-ph↗

arXiv2007

Lband radiometric behaviour of pine forests for a variety of surface moisture conditions

From July-December 2004 the experimental campaign 'Bray 2004' was conducted in the coniferous forest of Les Landes near Bordeaux, France, using a multi-angle L-band (1.4 GHz) radiometer to measure upwelling radiation above the forest. At the same time, ground measurements were taken of soil and litter moisture content. This experiment was done in the context of the upcoming SMOS mission in order to improve our understanding of the behaviour of the L-band signal above forested areas. Very little information exists on this subject at the moment, especially for varying hydrological conditions. Furthermore, additional measurements were done at the University of Bordeaux (PIOM laboratory) to determine the dielectric behaviour of a litter layer such as that found at the Bray site. There is some evidence that this layer may have a different influence on the L-band signal than either the soil or the vegetation, however the exact behaviour of the litter layer and the extent of its influence on the L-band signal are as yet unknown. This paper presents 1) results of the Bray experiment describing the behaviour of the above-canopy L-band emissivity for different conditions of ground moisture and 2) the relationship between soil and litter moisture content and results of the laboratory experiments on litter dielectric properties. Together this will give a first insight into the L-band radiometric properties of the different forest layers for varying hydrological conditions.

physics.geo-ph↗

arXiv2007

Travaux pratiques sur les réseaux locaux de type WIFI utilisant des simulations numériques des phénomènes de propagation des ondes électromagnétiques

The wireless network technology WiFi finds more and more applications in the industrial field as for the exchange of information between the people or the equipment. It has the advantage of allowing a great flexibility of the network but requires precautions of installation to be effective (flow, reliability...). The fitter of such a network must have knowledge to install and configure the materials (access points, wifi interface) but also of knowledge in propagation of electromagnetic waves which is the support of the transmission of data. The teaching of this technology requires practical works which must make it possible for the student to implement this knowledge. This article presents the various means of calculations which we implemented within the framework of practical works to allow the student to visualize and thus to better control the phenomena of propagation existing in a WiFI network.

physics.ed-ph↗

arXiv2007

Etude Des Signaux Recueillis Par Un Radar Embarque Sur Un Vehicule En Deplacement. Application a L'Interpretation Des Signaux Recoltes Par Le Radar Wisdom De la Mission Spatiale Exomars

The ExoMars mission of the program Aurora (ESA) aims to send a vehicle (Rover) on Mars in 2013. Beyond the technological aspects of the mission, the Rover will also carry scientific instruments for the analysis of Mars subsurface to search traces of past or present life in the Martian soil. The Rover will embark a drilling machine which will give access to samples of sub-surface of Mars to 2 meters depth. This constitutes the great originality of ExoMars, because the Mars sub-surface remains still unknown and seems to be the best place to shelter good conditions to create life. This drilling machine will be guided by a radar system sounder UHF, the WISDOM instrument, which will also make possible to probe the Mars sub-surface to a few meters of depth to detect water and to study the geological structures. We have analytical and numerical electromagnetic models to simulate the behavior of an electromagnetic wave in the Mars sub-surface, but also to simulate the interactions between the wave and the structure of the Rover. The objective of the work which we present consists in the study of the factors able to create disturbances of measurements in order to correct the effects on the measured signal. Initially we present the solution which we retained in order to be able during the same calculation to simulate the displacement of the Rover on several tens of meters. We also present the results relating to the effect of the orientation of the antenna during displacement due to topography of the observation site.

physics.geo-ph↗

arXiv2007

Inversion model validation of ground emissivity. Contribution to the development of SMOS algorithm

SMOS (Soil Moisture and Ocean Salinity), is the second mission of 'Earth Explorer' to be developed within the program 'Living Planet' of the European Space Agency (ESA). This satellite, containing the very first 1.4GHz interferometric radiometer 2D, will carry out the first cartography on a planetary scale of the moisture of the grounds and the salinity of the oceans. The forests are relatively opaque, and the knowledge of moisture remains problematic. The effect of the vegetation can be corrected thanks a simple radiative model. Nevertheless simulations show that the effect of the litter on the emissivity of a system litter + ground is not negligible. Our objective is to highlight the effects of this layer on the total multi layer system. This will make it possible to lead to a simple analytical formulation of a model of litter which can be integrated into the calculation algorithm of SMOS. Radiometer measurements, coupled to dielectric characterizations of samples in laboratory can enable us to characterize the geological structure. The goal of this article is to present the step which we chose to validate this analytical model.

physics.geo-ph↗