Observations of fireballs and space debris with the BRAMS network : preliminary results

BRAMS (Belgian RAdio Meteor Stations) is a Belgian forward-scatter radio network dedicated to meteor observations, using 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 340 W. As a consequence, the range of meteor echoes is not directly available, and the reconstruction of meteoroid trajectories and velocities relies on time delays between meteor echoes observed at multiple receiving stations, complemented by pre-t0 phase curves (Balis et al., 2025).

These techniques benefit from the specular reflection of radio waves on ionized meteor trails, which is generally valid for underdense and intermediate meteor echoes. In the case of fireballs, however, trail echoes often become overdense and may exhibit non-specular reflections. On the other hand, some fireballs also produce head echoes whose reflections appear to remain compatible with the specularity condition.

We present preliminary results on constraining fireball velocities by measuring the slope of meteor head echoes observed at several receiving stations. This task is challenging because the available frequency bandwidth is often limited by overlap with trail echoes, contamination from sometimes strong airplane reflections, or low signal-to-noise ratio (SNR) in parts of the echo. To assess the quality of the derived velocities, we analyse BRAMS observations associated with 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 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, above northern France, the event was clearly detected by several stations, mainly in southern Belgium and France. We apply the same head-echo analysis technique to constrain the velocity and investigate possible early deceleration. In addition, a few stations recorded very clear pre-t0 phase curves with excellent SNR, opening the possibility of an independent velocity determination.

These preliminary results illustrate both the future capabilities of the BRAMS network for fireball and space-debris observations and the remaining challenges to be addressed.

Balis J., Lamy H., Anciaux M., Jehin E., De Keyser J., Kastinen D., Brown P. G.,  Enhanced Meteoroid Trajectory and Speed Reconstruction Using a Forward Scatter 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.