1. Hervé Lamy & Cédric Tétard Royal Belgian Institute for Space Aeronomy
Retrieving meteoroids trajectories using BRAMS data : preliminary simulations
Hervé Lamy & Cédric Tétard
Royal Belgian Institute for Space Aeronomy
METRO annual meeting 2016
Brussels – 29 November 2016

2. Forward scattering of radio waves

3. Specular reflection
Wislez et al (2005)
= 0

4. x (and y,z) of tangential point
Specular reflection
2 equations for a & b
x (and y,z) of tangential point

5. Idea of Nedeljkovic (2005)
If n receiving stations detect the same meteor, then the meteoroid trajectory must be tangential to a set of ellipsoids with a common focus T and various focii R1, R2, R3

6. Model for simulations
106 trajectories are simulated using a point (intersection of the trajectory and the ground) and a direction (two angles for elevation θ and azimuth ϕ). We calculate the positions of each tangential point for several combinations T-R1, T-R2, …

7. First criterion
Altitude of the reflection point must lie between 95 and 110 km

8. Number of trajectories remaining
With 3 stations, Uccle, Ottignies and Seneffe
95 < zp < 110 km U
65631 O
65344 S
67870
U & O
61186
O & S
57003
U & O & S
54734
The number of remaining trajectories does not decrease drastically when O and S are added to U, probably because of the rather similar T-R geometry for the 3 stations.

9. Second criterion
Power received at a given station must be > W
Numerator :
  6m, PT = 150 W, re = Bohr radius
 = polarisation
GT (,) and GR (,) are antenna gains
 : electron line density at the specular point

10. Polarisation
Can only be measured using a crossed Yagi antenna (in BEHUMA or BEUCCL)
Otherwise, assume we receive 50% of the power (so sin2  = ½)
Assumption to check statistically on a large set of meteor echoes observed at Humain or Uccle

11. Influence of electron line density
Uccle Station

12. Third criterion : time delays
For each remaining trajectory, we compute the distance between tangent points and the corresponding time delays (assuming the velocity of the meteor) and we choose the trajectory that matches the observed time delays.
Dourbes
Ottignies
Seneffe
Uccle
One possible trajectory and position of the 3 tangential points .
For all the computed trajectories, the distribution of the simulated delays
V=20 km/s

13. Example of detection of the same meteors in Uccle, Seneffe and Ottignies

14. Conclusions & perspectives
Method of Nedeljkovic difficult to apply in practice but useful for simulations & comparisons with optical observations
To be done: try reconstruction from observations from at least 6 stations (3 DF for one point, 2 for direction, 1 for speed). In practice : very often difficult to find data from at least 6 stations. New strategy for future receiving stations.

15. BEGRIM
BEOTTI
BEHAAC
BESENE
BEKAMP
BEUCCL

16. Conclusions & perspectives
Next step: reconstruction from observations of the interferometer + 3 stations nearby (only 4 DL left)
Not enough stations close to Humain
Install 3 new stations close to Humain in early 2017