Speaker
Description
BRAMS (Belgian RAdio Meteor Stations) is a Belgian forward-scatter radio network dedicated to meteor observations, consisting of a dedicated transmitter and more than 50 receiving stations located in Belgium and neighbouring countries. The transmitter emits a continuous-wave signal at 49.97 MHz with a power of approximately 350 W. As a consequence of the forward-scatter geometry, the range to a meteor echo is not measured directly, and the reconstruction of meteoroid trajectories and velocities relies on time delays between echoes observed at multiple receiving stations, complemented by pre-t0 phase curves (Balis et al., 2025).
These techniques rely on specular reflection of radio waves from ionized meteor trails, an assumption that is generally valid for underdense and intermediate meteor echoes. For fireballs, however, trail echoes often become complex and turbulent and may exhibit non-specular reflections. Some fireballs also produce head echoes, which can provide additional constraints on their trajectories and velocities.
We present preliminary results on the determination of fireball velocities and trajectories using two different methods. The first is based on the frequency-time slope of meteor head echoes observed at several receiving stations. This approach is challenging because the usable frequency range of the head echo is often limited by overlap with the trail echo, contamination by strong aircraft reflections, or a low signal-to-noise ratio (SNR) in the upper part of the echo. The second method uses the Fresnel transform introduced by Elford (2004). To assess the quality of the derived velocities and trajectories, we analyse
BRAMS observations of well-documented fireball events simultaneously observed by the FRIPON optical network (Colas et al., 2020).
On 27 August 2024, the uncontrolled re-entry of a Starlink satellite produced a bright fireball that was widely observed by the public, with more than 450 witness reports submitted to the IMO fireball database. Although the initial part of the trajectory was located south of the BRAMS network, over northern France, the event was clearly detected by several receiving stations. We apply the same two methods to the associated head echoes to constrain the velocity and trajectory of the satellite. The results are compared with trajectories derived from visual observations, TLE data, and seismo-acoustic observations (Eickhoff et al., 2026).
These preliminary results illustrate the potential of the BRAMS network for future fireball and space-debris observations, as well as the remaining methodological challenges that need to be addressed.
Balis J., Lamy H., Anciaux M., Jehin E., De Keyser J., Kas nen D., Brown P. G., Enhanced Meteoroid Trajectory and Speed Reconstruc on Using a Forward Sca er Radio Network: Pre-t0 Phase Technique and Uncertainty Analysis, Radio Science, Volume 60, Issue 8, 2025
Colas, F. et al, FRIPON: a worldwide network to track incoming meteoroids. Astronomy & Astrophysics, Volume 644, 2020.
Eickoff, D. Et al, Re-entry and burn up of Starlink-2382 satellite: estimating trajectory and ablation coefficient from acoustic and coupled seismic waves, Geophysical Journal Interna onal, 246, 2026.
Elford, W.G., Radar observa ons of meteor trails, and their interpretation using Fresnel holography: a new tool in meteor science, Atmospheric Chemistry and Physics, 2004.