In the last months, the Belgian Institute for Space Aeronomy has been developing a Belgian network for observing radio meteors using forward scattering technique. This network is called BRAMS for Belgian RAdio Meteor Stations. Two beacons emitting a circularly polarized pure sine wave toward the zenith act as the transmitters at frequencies of 49.97 and 49.99 MHz. The first one located in Dourbes (Southern Belgium) emits a constant power of 150 Watts while the one located in Ieper (Western Belgium) emits a constant power of 50 Watts. The receiving network consists of about 20 stations hosted mainly by radio amateurs. Two stations have crossed-Yagi antennas measuring horizontal and vertical polarizations of the waves reflected off meteor trails. This will enable a detailed analysis of the meteor power profiles from which physical parameters of the meteoroids can be obtained. An interferometer consisting of 5 Yagi-antennas will be installed at the site of Humain in order to determine the angular detection of one reflection point, allowing us to determine meteoroid trajectories. We describe this new meteor observing facility and present the goals we expect to achieve with the network

Calders, S.

De Keyser, J.

Gamby, E.

Lamy, H.

Ranvier, S.

Verbeeck, C.

NASA Technical Reports Server

BRAMS:  the Belgian RAdio Meteor Stations 
 
H. Lamy1• S. Ranvier • J. De Keyser • S. Calders • E. Gamby • C. Verbeeck2 
 
 
 
Abstract  In the last months, the Belgian Institute for Space Aeronomy has been developing a Belgian 
network for observing radio meteors using forward scattering technique. This network is called BRAMS 
for Belgian RAdio Meteor Stations. Two beacons emitting a circularly polarized pure sine wave toward 
the zenith act as the transmitters at frequencies of 49.97 and 49.99 MHz. The first one located in 
Dourbes (Southern Belgium) emits a constant power of 150 Watts while the one located in Ieper 
(Western Belgium) emits a constant power of 50 Watts. The receiving network consists of about 20 
stations hosted mainly by radio amateurs. Two stations have crossed-Yagi antennas measuring 
horizontal and vertical polarizations of the waves reflected off meteor trails. This will enable a detailed 
analysis of the meteor power profiles from which physical parameters of the meteoroids can be obtained. 
An interferometer consisting of 5 Yagi-antennas will be installed at the site of Humain in order to 
determine the angular detection of one reflection point, allowing us to determine meteoroid trajectories. 
We describe this new meteor observing facility and present the goals we expect to achieve with the 
network.  
 
Keywords  radio meteors · forward scattering 
 
 
 
1  Introduction 
 
The Earth’s atmosphere is constantly hit by thousands of meteoroids with sizes ranging from 
submillimeters to several meters. Their estimated cumulative mass is in the range [40-100] tons per day. 
They play a crucial role in a number of astronomical and aeronomical studies and, given their intercept 
velocities in excess of 11 km/s, they pose a significant threat to spacecraft. Traditionally, they have been 
detected by visual means or with radars during their interaction with the atmosphere. Here we propose to 
study the meteoroid population with the BRAMS (Belgian RAdio Meteor Stations) network, a set of 
radio receiving stations using forward scattering techniques and two dedicated beacons as transmitters. 
The BRAMS network will be finished by the end of 2010. Its current state is described in section 2 
while section 3 is devoted to the objectives of the project. In the conclusion, the advantages of a forward 
scattering system over traditional radar systems will be shortly discussed. 
 
 
2  The BRAMS Network 
 
In 2009 the Belgian Institute for Space Aeronomy (BISA) initiated the development of BRAMS, a 
Belgian network of radio receiving stations using forward scattering techniques to detect meteors.  This  

H. Lamy ( )$&*+
	<$=>	?	QX	<$&Y"	<X$[\]Q 
Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium. E-mail: herve.lamy@aeronomie.be 
 
C. Verbeeck 
Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels, Belgium

https://ntrs.nasa.gov/search.jsp?R=20110016622 2019-08-29T18:25:06+00:00Z
project is carried out in collaboration with about 20 Belgian radio amateurs or groups of amateur 
astronomers which will host several stations throughout the country (see black squares on Figure 1). 
 
 
Figure 1.  Geographical distribution of the stations of the BRAMS network. The black squares represent the 
receiving stations while the two triangles represent the two beacons (Ieper in the West and Dourbes in the South-
East). The biggest cities of Belgium, represented by rhombs, have been added to facilitate identification of the 
stations.  
 
 
 The transmitters are two dedicated beacons located in Ieper and Dourbes (the two triangles on 
Figure 1). They emit a pure sinusoidal wave with a constant power of respectively 50 and 150 watts, at 
frequencies respectively of 49.99 and 49.97 MHz. These frequencies are protected avoiding ambiguity 
about the origin of detected meteor echoes. The beacon in Ieper is a crossed 2-element Yagi antenna 
which has been constructed in 2008 by radio amateurs from the VVS (Vereniging Voor Sterrenkunde -
Flemish association of amateur astronomers). It emits toward the zenith with a HPBW (Half-Power 
Beam Width) of ~100° (see Figure 2) which covers a large surface of the sky at altitudes between 90 and 
120 km. The theoretical total gain of this antenna is 5.9 dBi. The beacon in Dourbes is under 
construction and will be active in September 2010. It will be similar to the one in Ieper but will use a 
8m× 8m grid as the reflector to increase the power emitted upward (HPBW ~64°
 
-see Figure 2). With 
this grid, the total gain is increased by 3.6 dB as compared to the Ieper beacon. The stability of the 
frequency of the Dourbes beacon is secured with a GPS disciplinated OCXO (Oven-Controlled Crystal 
Oscillator) 10 MHz reference.  
 A typical receiving station is made of a 3-element Yagi antenna linked to a ICOM ICR75 
receiver by a coaxial cable. The received signal is sampled and stored on a local PC. With 20 receiving 
stations spread over Belgium, we will increase both the number of meteor detections and the chances of 
having the same meteor detected simultaneously by several stations. This last point is essential for the 
determination of meteoroid trajectories since each detection gives information only about one point of 
the trajectory. This requires a very good synchronization of the stations. The stations will be 
synchronized by using the NTP (Network Time Protocol) application and a local GPS as reference 
clock. Accuracy of 1 ms is expected. Each station will generate approximately 1 GB of data per day. 
First these data will be temporarily stored on local hard disks then later archived with the IT facilities of  

 
 
Figure 2.  Theoretical radiation pattern (in dB) of the two beacon antennas (circularly polarized). 
Solid line: Dourbes beacon (with a 8m  8m grid). Dashed line: Ieper beacon. 
 
 
BISA, where all data will be analyzed and become available to the scientific community. In these data 
there will be a large number of meteor echoes but also a large number of “spurious” echoes such as 
reflection of radio waves on planes, sporadic Es, thunderstorms, etc. as well as local broad-band 
interferences. A software is currently developed to automatically select meteor echoes only.  
The station in BISA (located in Uccle in the South of Brussels) is also equipped with an 
additional antenna, a crossed 3-element Yagi, connected to a low noise amplifier (MITEQ AU-1138) 
and a software defined radio receiver (USRP2). With this setup, we will measure both polarizations 
(horizontal and vertical) of the meteor echoes and combine them to obtain the total power reflected by 
the meteor. This will allow us to perform quantitative analyses of the signal in order to retrieve physical 
parameters of the meteoroids. 
 An interferometer made of 5 Yagi antennas will be installed in the radio astronomical site of 
Humain in order to determine the angular direction of one reflection point with an accuracy Á 1-2°. 
Humain is located at approximately 60 km north-east of Dourbes. We will use the 5 antenna 
configuration of [8] consisting of two orthogonal linear arrays of 3 antennas with the central one 
common to both arrays.  The central antenna will be a crossed 3-element Yagi antenna used in order to 
obtain the total power of the incoming waves like in the BISA station. To get information on the angular 
direction of the reflection point, the phase of the signals from the 5 antennas are compared. For this 
purpose, the analog-to digital converters of the five USRP2 receivers are synchronized. In addition, the 
frequency stability of the receivers is ensured by a 10 MHz reference similar to the one used for the 
beacon in Dourbes. 
 

3  Objectives of the Project 
 
By using the BRAMS network, we plan to reach the objectives described below. They are separated 
according to whether they can be achieved with a single station, with several stations or with several 
stations and the interferometer.  
 
1. By using data from a single receiving station, the activity profiles of meteor showers (number of 
echoes versus time) can be obtained by subtracting sporadic meteor echoes from all echo counts. 
These activity profiles must be corrected for the observability function of the station, which 
describes its sensitivity for detecting meteoroid echoes from a specific direction in the sky ([7], 
[15], [13]). The activity profiles of the main meteor showers will be studied and compared to 
results in the literature. Mass indexes and flux densities will be calculated for meteor showers 
and sporadic background using the method developed by [1] and [11], [12]. 
 
2. Simultaneous detection of a meteor by several stations allows in principle to retrieve some 
information about the meteoroid trajectory. We will test a method proposed by [9] exploiting the 
fact that a meteor trail is tangential to a family of ellipsoids with the receivers as one focal point 
and the transmitter as the other one (specularity condition). If the meteor is also detected by the 
interferometric station in Humain, the problem is simplified since then we know the angular 
direction of the reflection point for this particular geometry. The height of this reflection point 
can be obtained for shower meteors but is still unknown for sporadic meteors. However, for 
underdense meteors, it can be estimated from the exponential decay of the power profile (with 
the use of a good atmospheric model such as MSISE-00) and for overdense meteors, it can be 
estimated with the method proposed by [5]. With the 3-D position of one specular point and with 
detections of the meteor by other stations, we can retrieve the trajectory of the meteoroid even 
for sporadic meteors ([16]). Eventually the goal is to produce a map in Sun-centered ecliptical 
coordinates of the distribution of meteor radiants and to compare it to similar ones obtained by 
optical or radar means (e.g. [4]). 
 
3. For a given meteor, when the geometry is fully resolved, the study of the power profiles give 
access to several important physical parameters if the technical characteristics of the receiving 
station (antenna gains, polarization of the reflected wave, calibration of the acquisition card, etc.) 
are perfectly known [16]. These characteristics will only be known for the stations in BISA and 
in Humain. For the others, we will only have reasonable estimates. The electron line density at 
the reflection point can be computed from the maximum of the power profile. If the electron line 
density is obtained in several points of the meteoroid trail (from multi-station observations), the 
initial mass of the meteoroid can be estimated with models of meteoroid ablation in the Earth’s 
atmosphere (e.g. [3]). The ambipolar diffusion coefficient can be obtained from the exponential 
decay of underdense meteors and yields information on the meteor’s height. The speed of the 
meteoroid can be determined by several methods: a) from Fresnel oscillations if these are present 
and if the signal-to-noise ratio of the data is large enough, b) from initial rise times of the power 
profiles if the meteor is observed by several stations (requiring a good synchronization from the 
various stations) and c) from the Doppler effect for head echoes (see below). 
 
4. Head echoes are associated with the ionized region in front of the meteoroid. Therefore, these 
echoes in spectrograms show a large Doppler effect due to the high velocity component of the 

object along the line-of-sight. If such an echo is detected by at least 3 stations, we can in 
principle retrieve the total velocity of the meteoroid [10], [14]. In combination with an ablation 
model, the meteoroid mass and density can be estimated. Comparison with the results on head 
echoes obtained with High-Power Large-Aperture radars will be considered. 
 
5. Once we have the radiant of individual meteors and also an estimate of the relative intercept 
velocity of the incoming particle, the next step is to calculate the orbital parameters of the 
detected meteoroids. A correction must be applied for the acceleration produced by the 
gravitational focusing of Earth as well as for the Earth’s heliocentric velocity. Knowing the 
orbital parameters contributes to a better understanding of the distribution and evolution of 
material in the Solar System. 
 
6. Another advantage of having stations with dual polarized antennas is the ability to investigate the 
polarization of the received waves. Since most of receiving stations can detect only one 
polarization, it is very important to determine the depolarization coefficient of the reflections on 
the meteor trail. The rotation of the polarization plane of the incoming wave can be due to 
ionospheric Faraday rotation or as a result of the scattering from meteor trails. We will 
investigate whether the depolarization depends on the type, the trajectory, or the size of the 
meteor trail. To our knowledge, very few similar measurements have been done with a forward-
scatter system (see however [2]). 
 
 
4  Conclusion 
 
The BRAMS network will be a very useful tool to better characterize the distribution of meteoroids in 
the Solar System. Most researchers employ a backscatter set-up rather than a forward-scatter system, as 
the latter has a much more complicated geometry. However, backscatter systems suffer from the echo 
ceiling selection effect, which limits their views on faint and fast meteors. Forward-scatter setups are 
much less vulnerable to this selection effect, hence yielding a less biased meteoroid population. To our 
knowledge, there are only two other forward-scatter systems run by professional astronomers: the 
Bologna-Lecce-Modra system [6] and the HRO system at the Kochi University in Japan [17]. The 
former has only 2 receiving stations and no interferometric capabilities while the latter has only 6 
stations. BRAMS will feature at least 20 stations that will allow improved multi-station analysis and will 
also have the additional advantage of an interferometric system. 
 
 
Acknowledgements 

BRAMS is a project of the Belgian Institute for Space Aeronomy which is funded by the Belgian Solar-
Terrestrial Center of Excellence (STCE -http://www.stce.be). This project is carried out in collaboration 
with many radio amateurs from Belgium, in particular with several members from the VVS (Vereniging 
Voor Sterrenkunde). We would like to thank them for their participation in this project. 
 
 
 
 
 

References 
 
1. Belkovich O. et al., Processing of radar observations, Proceedings of the Radio Meteor School 2005, Oostmalle, Eds. C. 
Verbeeck and J.-M. Wislez, (2006).  
2. Billam E.R. & Browne I.C., Characteristics of Radio Echoes from Meteor Trails IV: Polarization Effects, Proceedings 
of the Physical Society, section B, Volume 69, Number 1, (1955).  
3. Campbell-Brown M.D., Koschny D., Model of the ablation of faint meteors, A&A, 418, 751-758, (2004).  
4. Campbell-Brown M.D., High Resolution radiant distribution and orbits of sporadic radar meteoroids, Icarus 196, 144-
163, (2008).  
5. Carbognani A., De Meyere M., Foschini L., Steyaert C., On the meteor height from forward scatter radio observations, 
A&A,361, 293-297, (2000).  
6. Cevolani G. et al, Baseline effect on the forward scatter radar reflections from meteor trains, Il Nuovo Cimento C, 19, 
447-450, (1996)  
7. Hines C.O., Diurnal variations in the number of shower meteors detected by the forward-scattering of radio waves -Part 
III. Ellipsoidal theory, Can. J. Phys., 36, 117-126 (1958).  
8. Jones J., Webster A.R., Hocking W.K., An improved interferometer design for use with meteor radars, Radio Sci., 33, 
55-65 (1998).  
9. Nedeljkovic S., Meteor forward scattering at multiple frequencies, Proceedings of the Radio Meteor School 2005, 
Oostmalle, Eds. C. Verbeeck and J.-M. Wislez, (2006).  
10. Richardson J. & Kuneth W., Revisiting the radio Doppler effect from forward-scatter meteor head echoes, WGN, 
Journal of the International Meteor Organization, 26, 117-130, (1998).  
11. Ryabova G.O., Calculation of the incident flux density of meteors by numerical integration I, WGN, Journal of the 
International Meteor Organization, 36, 120-123, (2008).  
12. Ryabova G.O., Calculation of the incident flux density of meteors by numerical integration II, WGN, Journal of the 
International Meteor Organization, 37, 63-67, (2009).  
13. Steyaert C., Brower J., Verbelen F., A numerical method to aid in the combined determination of stream activity and 
Observability Function, WGN, Journal of the International Meteor Organization, 34, 87-93, (2006).  
14. Steyaert C., Verbelen F. et al, Meteor Trajectory from Multiple Station Head Echo Doppler Observations, submitted to 
WGN.  
15. Verbeeck C., Calculating the sensitivity of a forward scatter setup for underdense shower meteors, Proceedings of the 
International Meteor Conference 1996 (Eds. A. Knöfel and P. Roggemans), 122-132 (1997).  
16. Wislez J-M., Meteor astronomy using a forward scatter set-up, Proceedings of the Radio Meteor School 2005, 
Oostmalle, Eds. C. Verbeeck and J.-M. Wislez, (2006).  
17. Yamamoto M.-Y. et al, Development of HRO interferometer at Kochi University of Technology, Proceedings of the 
International Meteor Conference 2006, Eds. F. Bettonvil & J. Kac, 117-125, (2007). 
 
 
 



BRAMS: The Belgian RAdio Meteor Stations

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server