Interferometry Improved Wind Retrieval from BRAMS Forward-Scatter Meteor Radar Observations

The Belgian RAdio Meteor Stations (BRAMS) network is used to analyse the dynamics of the upper atmosphere at altitudes of 80 to 110 km, also known as Mesosphere-Lower Thermosphere (MLT), towards a better understanding of the coupling between atmospheric layers [1].

BRAMS is a Continuous Wave (CW) forward-scatter radar using a dedicated transmitter and more than 50 receiving stations located in Belgium and neighbouring countries. The transmitter emits a pure sine wave without modulation at 49.97 MHz with a power of approximately 340 W. Although BRAMS operates with lower transmitted power than classical meteor radars, this can be partly compensated by its large number of receiving stations, which may provide multiple reflection points for a single meteor and therefore sample a substantial portion of an individual trajectory.

In this work, the effect of radio interferometry on the wind field calculation is analysed. Since there is no range information available for a CW radar like BRAMS, the position of the meteor’s specular reflection point, which is required to calculate the wind speeds, is derived from the meteor trajectory reconstruction using the trajectory reconstruction tool pyBRAMS [2,3]. Providing pyBRAMS with angle of arrival data for meteors seen by the interferometer improves the meteor trajectory reconstruction and hence improves the geometric information required for the wind retrieval.

The first results show that the meteor observations and hence the trajectory reconstruction using BRAMS are sufficient for wind retrieval. The additional information provided by the interferometry delivers improved trajectories producing more accurate specular point calculations and hence an improved wind field. However, at the present stage, only a limited data set of events was retained after quality filtering ensuring sufficient signal-to-noise ratio and excluding contamination by other signals such as airplane reflections. Further optimization on the event selection is subject of future work to increase the number of events available for wind retrieval. Additionally, higher-order wind velocity effects need to be analysed.

Overall, this study gives a first assessment of the effect of radio interferometry on the BRAMS wind retrieval signal-processing chain. It demonstrates how interferometry improves the wind speed estimates using a low-power CW forward-scattering radar like BRAMS, which has no range information available for meteor events.

References

• [1] Stober, G., and J. L.Chau, Radio Science 2015, 50, 431–442.
• [2] Balis J., Lamy H., Anciaux M., Jehin E., Radio Science 2023, Volume 58, Issue 6.
• [3] Balis J., Lamy H., Anciaux M., Jehin E., De Keyser J., Kastinen D., Brown P. G., Radio Science 2025, Volume 60, Issue 8.