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Abstract :
[en] When meteoroids hit Earth’s atmosphere molecules, a trail of plasma located downstream of the meteoroid is created. This region, composed of free electrons and positively charged ions, is capable of reflecting radio signals. The reflection on the plasma trails is usually assumed to be specular, which means that the radio wave is reflected only at a given point along the meteoroid trajectory. For forward scatter systems, the position of this specular point depends on the trajectory on the one hand, and on the position of both the emitter and the receiver on the other hand. Using non-collocated receivers, one obtains several specular points along the trajectory. The receivers will thus detect the reflected signal at different time instants on a given trajectory. In this work, we introduce a method that aims at reconstructing meteoroid trajectories using only the time differences of the meteor echoes measured at the receivers of a forward scatter radio system. Assuming a constant speed motion, the position (three degrees of freedom) and the three velocity components have to be determined. Two alternative formulations to solve this complex problem through non-linear optimization are compared. The first one is based on the minimization of the bistatic range, while the second looks for the tangent line to several ellipsoids. A Monte-Carlo analysis is performed to highlight the sensitivity of the output trajectory parameters to the input time differences. The application of this method to actual radio observations from the BRAMS (Belgian RAdio Meteor Stations) network is also presented. The post-processing steps allowing to extract meteor echoes from the raw radio signals are described. For comparison about the quality of trajectory reconstruction, data from the optical CAMS-BeNeLux network are used. Promising results showing the reconstructed position, velocity and inclination of several meteoroid trajectories are discussed.
