BRAMS: The Belgian RAdio Meteor Stations

Lamy, H.; Ranvier, Sylvain; Keyser, Johan De; Gamby, E.; Calders, Stijn

doi:10.1109/ursigass.2011.6050925

Cited by 4 publications

(1 citation statement)

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“…Recent efforts have been made by the Belgian Institute for Space Aeronomy to predict velocity, trajectory and mass of meteors. The Belgian RAdio Meteor Stations (BRAMS) experiment consists in a series of receivers spread all over Belgium to collect and standardize the meteor observations [3]. Ground radio stations are able to detect the free electrons concentration in the meteoroid wake, which is directly influenced by ablation mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Aerothermodynamic modelling of meteor entry flows in the rarefied regime

Bariselli

Boccelli

Magin

et al. 2018

2018 Joint Thermophysics and Heat Transfer Conference

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Due to their small size and tremendous speeds, meteoroids often burn up at high altitudes, above 80 km, where the atmosphere is rarefied. Ground radio stations are able to detect the free electrons concentration in the meteoroid wake, which is produced by hyperthermal collisions of the ablated species with the free-stream. The interpretation of radio data, however, currently relies on phenomenological methods, derived under the assumption of free molecular flow, hence, poorly accounts for the dynamics of the vapour, chemistry, and diffusion in the meteor trail. In this work, we aim to provide a detailed description of the flowfield around a meteoroid by means of Direct Simulation Monte Carlo and to obtain the evolution of the free electrons in the meteor wake via an extended trail simulation. An evaporation boundary condition is developed in the framework of an open source DSMC software. The material is assumed to be composed by a mixture of metal oxides which are typically present in ordinary chondritic meteorites. The transport properties of the ablated vapour are computed following the Chapman-Enskog theory and the DSMC phenomenological parameters are retrieved by fitting the collision integrals over a wide range of temperatures. As a last step, chemical and diffusion processes in the trail are computed. Starting from the baseline DSMC solution, our approach marches in time along the precomputed streamlines, calculating chemistry and radial diffusion for metals and free electrons. As study case, the flow around a 1 mm evaporating meteoroid is analysed at different altitudes. A high level of thermal nonequilibrium is appreciated in the head of the meteor, whereas in the trail, after a few diameters, the flow equilibrates. At lower densities, the vapour can travel upstream without interacting much with the incoming jet. On the other hand, at lower altitudes, re-condensation plays a significant role in the stagnation region. Finally, a trail, several meters long and formed by metallic species, generates behind the body. Ionization of sodium turns out to be the dominant process in the production of free electrons, whereas radial diffusion seems to prevail over recombination as depletion mechanism.

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Section: Introductionmentioning

confidence: 99%

Aerothermodynamic modelling of meteor entry flows in the rarefied regime

Bariselli

Boccelli

Magin

et al. 2018

2018 Joint Thermophysics and Heat Transfer Conference

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Aerothermodynamic modelling of meteor entry flows

Bariselli

Frezzotti

Hubin

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Due to their small size and tremendous speeds, meteoroids often burn up at high altitudes above 80 km, where the atmosphere is rarefied. Ground radio stations allow us to detect the concentration of electrons in the meteoroid trail, which are produced by hyperthermal collisions of ablated species with the freestream. The interpretation of these data currently relies on phenomenological methods, derived under the assumption of free molecular flow, that poorly accounts for the detailed chemistry, diffusion in the vapour phase, and rarefied gas effects. In this work, we employ the direct simulation Monte Carlo (DSMC) method to analyse the detailed flowfield structure in the surroundings of a 1 mm meteoroid at different conditions, spanning a broad spectrum of Knudsen and Mach numbers, and we extract resulting ionization efficiencies. For this purpose, we couple the DSMC method with a kinetic boundary condition which models evaporation and condensation processes in a silicate material. Transport properties of the ablated vapour are computed following the Chapman–Enskog theory starting from Lennard–Jones potentials. Semi-empirical inelastic cross-sections for heavy- and electron-impact ionization of metals are computed analytically to obtain steric factors. The ionization of sodium is dominant in the production of free electrons, and hyperthermal air–vapour collisions play the most important role in this process. The ionization of air, classically disregarded, contributes to the electron production as significantly as ionization of magnesium and iron. Finally, we propose that DSMC could be employed as a numerical experiment providing ionization coefficients to be used in synthetic models.

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