<p>BRAMS (Belgian RAdio Meteor Stations) is a network using forward scatter of radi... more <p>BRAMS (Belgian RAdio Meteor Stations) is a network using forward scatter of radio waves on ionized meteor trails to study meteoroids. It is made of a dedicated transmitter and of 42 receiving stations located in or near Belgium. The network started in 2010 but has recently been extended and upgraded.</p> <p>The transmitter emits a circularly polarized CW radio wave with no modulation at a frequency of 49.97 MHz and with a power of 130 W. Each receiving station uses a 3-element zenith pointing Yagi antenna. The first stations used analog ICOM-R75 receivers and a PC. Since 2018, new improved stations have been installed using digital RSP2 receivers, a GPSDO and a Raspberry Pi, providing better dynamic, sensitivity and stability.</p> <p>A vast majority of the meteor echoes detected by BRAMS are specular, which means that most of the power of the meteor echoes comes from a small region along the meteoroid path centered on the specular reflection point, a point which is tangential to a prolate ellipsoid having the transmitter and the receiver as the two foci. This puts important geometrical constraints on whether a specific meteoroid trajectory can be detected or not by a given receiving station since the position of the reflection point must fall within the so-called meteor zone.</p> <p>As a consequence, for meteor showers, the observed activity based on the raw counts of meteor echoes recorded by a BRAMS station is modulated by the position of the radiant throughout the day and does not truly reflect the real activity of the shower.  A possibility to correct these raw counts is to compute the so-called Observability Function (OF) introduced by Hines (1958) and further developed by Verbeeck (1997). This OF contains a geometrical part which provides the location of potentially observable meteor trails at a given moment and for a given station, and another part which takes into account which fraction of these trails will actually be detected by the receiving station.  Indeed, whether a meteor echo will be detected at the station also depends on the sensitivity of the receiving chain, on the power transmitted and on the ionization at the reflection point, the latter depending on the initial mass of the meteoroid.</p> <p>We will describe how the geometrical part of the OF is calculated and will provide results for several receiving stations of the BRAMS network to emphasize the importance of the geometry. We will also describe how we take into account important characteristics of the system to determine the sensitivity of the receiving chain such as the gains of the antenna in the direction of the meteor echoes.  Finally, we will apply the OF to the raw counts of a few main meteor showers (e.g. Perseids, Geminids, Quadrantids) obtained from the Citizen Science project, the Radio Meteor Zoo, that we have developed since 2016 in cooperation with Zooniverse (https://www.radiometeorzoo.be).</p> <p> </p> <p>Hines, C., Can. J. Phys., 36, 117-126, 1958</p> <p>Verbeeck, C., Proceedings of the International Meteor Conference, Apeldoorn, the Netherlands, 122-132, 1996</p>
<p>When meteoroids hit Earth’s atmosphere molecules, they leave a tra... more <p>When meteoroids hit Earth’s atmosphere molecules, they leave a trail of plasma behind. This region, composed of free electrons and positively charged ions, is capable of reflecting radio signals. The analysis of such signals along the meteoroid path can be used for various scientific purposes: quantification of the electron line density, analysis of the thermosphere properties, characterization of the meteor ablation process, etc. To achieve these objectives, the meteoroid trajectory needs first to be determined.  </p> <p>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. </p> <p>In this work, we propose 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, such as the BRAMS (Belgian RAdio Meteor Stations) network. The latter uses the forward scatter of radio waves on ionized meteor trails to study meteoroids falling in the Earth’s atmosphere. It is made of a dedicated transmitter and 42 receiving stations located in and nearby Belgium. Given that all the BRAMS receivers are synchronized using GPS clocks, we can compute the time differences of the meteor echoes and use them to find the meteoroid trajectory. </p> <p>Assuming a constant speed motion, the position (three degrees of freedom) and the three velocity components have to be determined. This inverse problem is non-linear and requires the definition of a target objective to minimize. Two different formulations are compared: the first one is based on the minimization of the bistatic range while the second one uses a forward model, which defines the trajectory as being tangential to a family of ellipsoids whose loci are the emitter and each receiver. A Monte-Carlo analysis is performed to highlight the sensitivity of the output trajectory parameters to the input time differences. </p> <p>The BRAMS network also includes an interferometer in Humain (south of Belgium). Unlike the other receiving stations, it uses 5 antennas in the so-called Jones configuration (Jones et al., 1998; Lamy et al., 2018) and allows to determine the direction of arrival of the meteor echo to within approximately 1°. In that case, the problem becomes much easier to solve because the interferometer gives information about the direction of a reflection point. The benefits brought by such a system regarding the accuracy of the trajectory reconstruction are highlighted. </p> <p>The post-processing steps allowing to extract meteor echoes from the raw radio signals are described. An approach to properly filter out the direct beacon signal is introduced. Indeed, each receiver detects a more or less strong direct signal coming from the transmitter. This signal does not contain any information about the meteor path since it simply propagates through the atmosphere and is not reflected on the meteor trail. Knowing that the BRAMS transmitter emits a continuous cosine wave, the amplitude, the frequency and the phase are fitted in the frequency domain. The beacon signal is finally reconstructed in the time domain and subtracted. This process in illustrated in the following figure, which shows an example of spectrograms (i.e. time-frequency maps where the power is color-coded) before and after the beacon signal subtraction. The proper removal of the horizontal line at around 1005 Hz (corresponding to the direct signal) is apparent in the bottom spectrogram. </p> <p> <img src="" alt="" width="1047" height="566" /></p> <p>Afterwards, a bandpass filter is necessary to fully exploit the echoes of the detected meteors. Indeed, the raw signal at the time of the meteor echo is noisy and can have interfering signals caused by the reflections on aircrafts. If the latter are at slightly different frequencies than the meteor echo, they produce interference beats. A windowed-sinc filter Blackman filter of high order is therefore used to remove the signal components at frequencies where the meteor echo does not appear. The time corresponding to half-peak power in the rising edge of the echo (which marks the passage of the meteoroid at the specular reflection point) is finally retrieved and the time differences are computed.  </p> <p>To analyze the accuracy of the trajectory…
<p>In May 2020, Europlanet Society launched a call to fund projects to enga... more <p>In May 2020, Europlanet Society launched a call to fund projects to engage the public with planetary science. Our project proposal called MOMSTER: MObile Meteor STation for Education & outReach was amongst the three projects that were granted.</p> <p>MOMSTER aims at developing a Meteor Education Kit as a resource for STEAM (Science, Technology, Engineering, Arts, Mathematics) teachers in secondary schools. The kit includes a mobile radio meteor station consisting of a dedicated antenna and radio receiver, as well as an educational package to learn all about meteors and their detection methods, while at the same time conveying a fascination for the ephemeral beauty and complexity of these natural light shows. The project goals are stimulating STEAM (ultimately resulting in nudging future career choices towards science or engineering career paths) and the use of citizen science (especially the Radio Meteor Zoo initiative on the online citizen science platform Zooniverse) at schools, and reaching the general public.</p> <p>The development of educational resources builds upon preliminary experiences we gained by participating in an Erasmus+ project called BRITEC (Bringing Research into ThE Classroom), in which teachers and pupils participated in the Radio Meteor Zoo activity.  We are presently in a pilot phase where three Belgian schools (two Dutch speaking and one French speaking) test the mobile radio meteor station and the educational resources, and give their feedback.</p> <p>We are using STEAM-education as an approach to broaden our target group towards less scientifically oriented students. We do this by developing an educational resource on visual (science) communication. We also organized an art & design competition for high school students with more than 30 submissions. The best piece of art will decorate the ‘MOMSTER boxes’ we use for transport of the radio receivers.</p>
METRO is the acronym for MEteor TRajectories and Origins. It is an interdisciplinary project with... more METRO is the acronym for MEteor TRajectories and Origins. It is an interdisciplinary project with a collaboration between several institutes. One of the main objective of this project is to determine the trajectories of meteors in the sky using the BRAMS network. This network relies on forward scattering of radio waves emitted by a beacon located in Dourbes off meteor ionization trails and received at 30 stations across Belgium. For some meteors, it will be possible to derive also the meteor speed. Thus, by combining trajectory and velocity, it is possible to trace back the orbit of the meteoroids.
The Royal Belgian Institute for Space Aeronomy (BISA) operates a network for radio meteor studies... more The Royal Belgian Institute for Space Aeronomy (BISA) operates a network for radio meteor studies based in Belgium. One of the receiving stations is located in the Humain Radio-Astronomy Station (HuRAS) and consists of an array of five 3-element Yagi antennas. In this paper the results of detailed numerical simulations are presented in order to obtain a first approach for the direction finding capability of this interferometer.
Because of the geometry associated with the forward-scatter method for observing meteors via radi... more Because of the geometry associated with the forward-scatter method for observing meteors via radio, knowing the radiation pattern of the involved antennas is essential to obtain parameters of scientific interest such as the meteoroid flux density. In this paper results of simulations of the antennas belonging to the Belgian RAdio Meteor Stations network (BRAMS) that are directly managed by the Belgian Institute for Space Aeronomy (BISA) are presented, as well as plans for verifying their patterns using an Unmanned Aerial Vehicle (UAV).
When using radio techniques to observe meteors, one way of gaining insights into the physical phe... more When using radio techniques to observe meteors, one way of gaining insights into the physical phenomena that produce the meteor echoes is by analyzing the radio polarization of meteor trail echoes (Billam and Browne, 1956; Sidorov et al., 1965; Cannon, 1986). For example, the time variation of the polarization of meteor echoes can, in principle, provide information about electron densities in the meteor trail as shown by Poulter and Baggaley (1977) and by Jones and Jones (1990). Furthermore, the physical phenomena that lead to specific signature of some echoes in the time-frequency domains, such as the multiple-branch echoes, the so-called “epsilons” (Steyaert, 2012), are still not fully understood. The analysis of the polarization of such echoes can be used to increase our knowledge in this field.
<p>BRAMS (Belgian RAdio Meteor Stations) is a network using forward scatter of radi... more <p>BRAMS (Belgian RAdio Meteor Stations) is a network using forward scatter of radio waves on ionized meteor trails to study meteoroids. It is made of a dedicated transmitter and of 42 receiving stations located in or near Belgium. The network started in 2010 but has recently been extended and upgraded.</p> <p>The transmitter emits a circularly polarized CW radio wave with no modulation at a frequency of 49.97 MHz and with a power of 130 W. Each receiving station uses a 3-element zenith pointing Yagi antenna. The first stations used analog ICOM-R75 receivers and a PC. Since 2018, new improved stations have been installed using digital RSP2 receivers, a GPSDO and a Raspberry Pi, providing better dynamic, sensitivity and stability.</p> <p>A vast majority of the meteor echoes detected by BRAMS are specular, which means that most of the power of the meteor echoes comes from a small region along the meteoroid path centered on the specular reflection point, a point which is tangential to a prolate ellipsoid having the transmitter and the receiver as the two foci. This puts important geometrical constraints on whether a specific meteoroid trajectory can be detected or not by a given receiving station since the position of the reflection point must fall within the so-called meteor zone.</p> <p>As a consequence, for meteor showers, the observed activity based on the raw counts of meteor echoes recorded by a BRAMS station is modulated by the position of the radiant throughout the day and does not truly reflect the real activity of the shower.  A possibility to correct these raw counts is to compute the so-called Observability Function (OF) introduced by Hines (1958) and further developed by Verbeeck (1997). This OF contains a geometrical part which provides the location of potentially observable meteor trails at a given moment and for a given station, and another part which takes into account which fraction of these trails will actually be detected by the receiving station.  Indeed, whether a meteor echo will be detected at the station also depends on the sensitivity of the receiving chain, on the power transmitted and on the ionization at the reflection point, the latter depending on the initial mass of the meteoroid.</p> <p>We will describe how the geometrical part of the OF is calculated and will provide results for several receiving stations of the BRAMS network to emphasize the importance of the geometry. We will also describe how we take into account important characteristics of the system to determine the sensitivity of the receiving chain such as the gains of the antenna in the direction of the meteor echoes.  Finally, we will apply the OF to the raw counts of a few main meteor showers (e.g. Perseids, Geminids, Quadrantids) obtained from the Citizen Science project, the Radio Meteor Zoo, that we have developed since 2016 in cooperation with Zooniverse (https://www.radiometeorzoo.be).</p> <p> </p> <p>Hines, C., Can. J. Phys., 36, 117-126, 1958</p> <p>Verbeeck, C., Proceedings of the International Meteor Conference, Apeldoorn, the Netherlands, 122-132, 1996</p>
<p>When meteoroids hit Earth’s atmosphere molecules, they leave a tra... more <p>When meteoroids hit Earth’s atmosphere molecules, they leave a trail of plasma behind. This region, composed of free electrons and positively charged ions, is capable of reflecting radio signals. The analysis of such signals along the meteoroid path can be used for various scientific purposes: quantification of the electron line density, analysis of the thermosphere properties, characterization of the meteor ablation process, etc. To achieve these objectives, the meteoroid trajectory needs first to be determined.  </p> <p>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. </p> <p>In this work, we propose 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, such as the BRAMS (Belgian RAdio Meteor Stations) network. The latter uses the forward scatter of radio waves on ionized meteor trails to study meteoroids falling in the Earth’s atmosphere. It is made of a dedicated transmitter and 42 receiving stations located in and nearby Belgium. Given that all the BRAMS receivers are synchronized using GPS clocks, we can compute the time differences of the meteor echoes and use them to find the meteoroid trajectory. </p> <p>Assuming a constant speed motion, the position (three degrees of freedom) and the three velocity components have to be determined. This inverse problem is non-linear and requires the definition of a target objective to minimize. Two different formulations are compared: the first one is based on the minimization of the bistatic range while the second one uses a forward model, which defines the trajectory as being tangential to a family of ellipsoids whose loci are the emitter and each receiver. A Monte-Carlo analysis is performed to highlight the sensitivity of the output trajectory parameters to the input time differences. </p> <p>The BRAMS network also includes an interferometer in Humain (south of Belgium). Unlike the other receiving stations, it uses 5 antennas in the so-called Jones configuration (Jones et al., 1998; Lamy et al., 2018) and allows to determine the direction of arrival of the meteor echo to within approximately 1°. In that case, the problem becomes much easier to solve because the interferometer gives information about the direction of a reflection point. The benefits brought by such a system regarding the accuracy of the trajectory reconstruction are highlighted. </p> <p>The post-processing steps allowing to extract meteor echoes from the raw radio signals are described. An approach to properly filter out the direct beacon signal is introduced. Indeed, each receiver detects a more or less strong direct signal coming from the transmitter. This signal does not contain any information about the meteor path since it simply propagates through the atmosphere and is not reflected on the meteor trail. Knowing that the BRAMS transmitter emits a continuous cosine wave, the amplitude, the frequency and the phase are fitted in the frequency domain. The beacon signal is finally reconstructed in the time domain and subtracted. This process in illustrated in the following figure, which shows an example of spectrograms (i.e. time-frequency maps where the power is color-coded) before and after the beacon signal subtraction. The proper removal of the horizontal line at around 1005 Hz (corresponding to the direct signal) is apparent in the bottom spectrogram. </p> <p> <img src="" alt="" width="1047" height="566" /></p> <p>Afterwards, a bandpass filter is necessary to fully exploit the echoes of the detected meteors. Indeed, the raw signal at the time of the meteor echo is noisy and can have interfering signals caused by the reflections on aircrafts. If the latter are at slightly different frequencies than the meteor echo, they produce interference beats. A windowed-sinc filter Blackman filter of high order is therefore used to remove the signal components at frequencies where the meteor echo does not appear. The time corresponding to half-peak power in the rising edge of the echo (which marks the passage of the meteoroid at the specular reflection point) is finally retrieved and the time differences are computed.  </p> <p>To analyze the accuracy of the trajectory…
<p>In May 2020, Europlanet Society launched a call to fund projects to enga... more <p>In May 2020, Europlanet Society launched a call to fund projects to engage the public with planetary science. Our project proposal called MOMSTER: MObile Meteor STation for Education & outReach was amongst the three projects that were granted.</p> <p>MOMSTER aims at developing a Meteor Education Kit as a resource for STEAM (Science, Technology, Engineering, Arts, Mathematics) teachers in secondary schools. The kit includes a mobile radio meteor station consisting of a dedicated antenna and radio receiver, as well as an educational package to learn all about meteors and their detection methods, while at the same time conveying a fascination for the ephemeral beauty and complexity of these natural light shows. The project goals are stimulating STEAM (ultimately resulting in nudging future career choices towards science or engineering career paths) and the use of citizen science (especially the Radio Meteor Zoo initiative on the online citizen science platform Zooniverse) at schools, and reaching the general public.</p> <p>The development of educational resources builds upon preliminary experiences we gained by participating in an Erasmus+ project called BRITEC (Bringing Research into ThE Classroom), in which teachers and pupils participated in the Radio Meteor Zoo activity.  We are presently in a pilot phase where three Belgian schools (two Dutch speaking and one French speaking) test the mobile radio meteor station and the educational resources, and give their feedback.</p> <p>We are using STEAM-education as an approach to broaden our target group towards less scientifically oriented students. We do this by developing an educational resource on visual (science) communication. We also organized an art & design competition for high school students with more than 30 submissions. The best piece of art will decorate the ‘MOMSTER boxes’ we use for transport of the radio receivers.</p>
METRO is the acronym for MEteor TRajectories and Origins. It is an interdisciplinary project with... more METRO is the acronym for MEteor TRajectories and Origins. It is an interdisciplinary project with a collaboration between several institutes. One of the main objective of this project is to determine the trajectories of meteors in the sky using the BRAMS network. This network relies on forward scattering of radio waves emitted by a beacon located in Dourbes off meteor ionization trails and received at 30 stations across Belgium. For some meteors, it will be possible to derive also the meteor speed. Thus, by combining trajectory and velocity, it is possible to trace back the orbit of the meteoroids.
The Royal Belgian Institute for Space Aeronomy (BISA) operates a network for radio meteor studies... more The Royal Belgian Institute for Space Aeronomy (BISA) operates a network for radio meteor studies based in Belgium. One of the receiving stations is located in the Humain Radio-Astronomy Station (HuRAS) and consists of an array of five 3-element Yagi antennas. In this paper the results of detailed numerical simulations are presented in order to obtain a first approach for the direction finding capability of this interferometer.
Because of the geometry associated with the forward-scatter method for observing meteors via radi... more Because of the geometry associated with the forward-scatter method for observing meteors via radio, knowing the radiation pattern of the involved antennas is essential to obtain parameters of scientific interest such as the meteoroid flux density. In this paper results of simulations of the antennas belonging to the Belgian RAdio Meteor Stations network (BRAMS) that are directly managed by the Belgian Institute for Space Aeronomy (BISA) are presented, as well as plans for verifying their patterns using an Unmanned Aerial Vehicle (UAV).
When using radio techniques to observe meteors, one way of gaining insights into the physical phe... more When using radio techniques to observe meteors, one way of gaining insights into the physical phenomena that produce the meteor echoes is by analyzing the radio polarization of meteor trail echoes (Billam and Browne, 1956; Sidorov et al., 1965; Cannon, 1986). For example, the time variation of the polarization of meteor echoes can, in principle, provide information about electron densities in the meteor trail as shown by Poulter and Baggaley (1977) and by Jones and Jones (1990). Furthermore, the physical phenomena that lead to specific signature of some echoes in the time-frequency domains, such as the multiple-branch echoes, the so-called “epsilons” (Steyaert, 2012), are still not fully understood. The analysis of the polarization of such echoes can be used to increase our knowledge in this field.
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