Combiner les énergies douces ?

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On the Analysis of Single-Doppler Radar Data

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Ball lightning seen from Puy de Dôme

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Infrared imagery applied to a large buoyant plume

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Soil moisture and vegetation biomass retrievals using L band, dual polarised and multi angular radiometric data in preparation of the SMOS mission

International audienceThe 2D L-band interferometer radiometer on board SMOS (Soil Moisture and Ocean Salinity) is based on an innovative bi-dimensional aperture synthesis concept. The sensor has new and very significant capabilities, especially in terms of multi-angular viewing configuration. In this study, the retrieval capabilities of SMOS, based on the actual system configuration have been assessed. From model simulations, the uncertainities on the retrieved variables is computed as a function of the uncertainties associated with both remotely sensed data (radiometric sensitivity /spl Delta/T, systematic bias) and model input parameters (errors are accounted for in the estimates of surface temperature and vegetation optical thickness, if one- or two-parameter retrievals are carried out). The simulations are performed using the /spl tau/-/spl omega/ approach, which provides accurate simulations of the passive microwave signature of the land surface at L-band. This study shows how and why the 2D interferometry concept, applied to Earth remote sensing from space, may bring a major qualitative improvement, thanks to the ability to obtain many data over a significant range of viewing angles. SMOS is the first mission which aims at demonstrating and using this feature. From the results of this study, promising retrieval capabilities can be expected from SMOS over the land surface

How the Saint Santin incoherent scatter system paved the way for a French involvement in EISCAT

This paper relates the development of a French incoherent scatter system which started its operations in 1965. This development took place several years after the initial implementation of such systems in the United States, in Peru and in the United Kingdom. The French system, owing to its bistatic configuration and the use of continuous waves, differed from the previous ones. These characteristics yielded signals of excellent spectral quality, unravelling the possibility of inferring physical parameters (Doppler shift, average ion mass) out of reach, at that time, of other systems. The possibility of making ion drift vector measurements led to extend the system into a quadristatic configuration. The multiple capabilities offered by the incoherent scatter technique, notably as concerns the thermodynamical properties of the ionosphere and of the thermosphere, led further the French community to a project of embarking an incoherent scatter radar on board a ship. Taking account of a project of a Scandinavian auroral zone radar and of the considerable interest of the study of auroral zone electrodynamics, the French community abandoned the idea of the ship and expressed an interest in joining the Scandinavian project in conjunction with Germany and the United Kingdom

Consequences of surface heterogeneity for parameter retrieval from 1.4-GHz multiangle SMOS observations

International audienceThe L-band (1.4 GHz) two-dimensional microwave interferometric radiometer, the payload of the Soil Moisture and Ocean Salinity (SMOS) mission, will observe elements of the Earth's surface simultaneously at multiple angles. Compared to single-angle observations, this multiangle observation technology is expected to significantly improve the capability of passive microwave remote sensing to retrieve soil moisture and vegetation properties from space. Although multiangle retrieval algorithms have been developed and successfully evaluated for homogeneous surfaces on the basis of simulation studies, the inherently large footprint of microwave observations from space has serious consequences for parameter retrieval from "real-world" inhomogeneous surfaces. At the spatial scale of SMOS (∼30 km for nadir observations), the Earth's surface is inhomogeneous almost by default. This aspect has not been fully accounted for yet. This study gives some insight into the consequences of vegetation spatial heterogeneity for the retrieval of "effective" surface parameters (soil moisture, canopy microwave transmissivity, and effective surface temperature) from inhomogeneous surfaces without prior knowledge of the within-pixel canopy heterogeneity

Triggered lightning strokes originating in clear air

International audienceDuring the 1978 campaign of the triggered lightning program at Saint-Privat d•'Allier (France), simultaneous data from a movie camera, a coaxial shunt amperometer, a network of electric field mills, and a weather radar, were collected during the initial phase of a particular triggered event. These data are shown to exhibit a high degree of consistency, leading to the conclusion that charges totaling several coulombs were present in cloudfree air in the vicinity of a stormy area