1. Study of joint CAMS/BRAMS observations & comparison with simulations
H. Lamy

2. Forward scatter radio observations
2 advantages:
Continuous monitoring
Sensitive to smaller masses
Duration of the meteor echo depends roughly on the size of the object
Most meteor echoes last a fraction of a second.

3. The BRAMS network
49.97 MHz
150 W
pure sine wave
circularly polarized

4. The BRAMS network University of Mons Maasmechelen Uccle Neufchâteau
Mons = Bergen
Uccle = Ukkel
Uccle
Neufchâteau

5. A typical receiving BRAMS station

6.  1 GB of data per day and per station
Example of BRAMS data
 3 MB per file every 5 min
 1 GB of data per day and per station
WAV-format

7. Spectrograms 200 Hz 5 minutes
NFFT = – overlap = 90%  t  0,34 sec (real  2,97 sec) and f  0,3 Hz

8. General idea
We are still struggling with the algorithms to retrieve meteoroid trajectories from BRAMS multi-stations observations.
Meanwhile we propose to use CAMS observations above Belgium which provide very accurate trajectories and speeds

9. CAMS observations
Credit : P. Roggemans
Provide very accurate trajectories, speed and deceleration measurements
Jenniskens et al (2016)

10. CAMS observations Night from 19 to 20 January : 245 trajectories
Trajectory 240 :
V_ =  0.15 km/s
a1 =  0.01 km/s
a2 =  0.08 s-1
Lat, Long, H of begin and end points of CAMS trajectory
Begin time of observation of CAMS trajectory

11. BRAMS observations : specularity condition

12. Red : CAMS visual trajectory
CAMS t_begin
CAMS t_end Tx
Rx1
Rx2
Rx3

13. CAMS/BRAMS 1st comparison
Night from 19 to 20/01/2017 : 245 trajectories
Trajectory 240
Not all stations were working nominally !

14. CAMS/BRAMS 1st comparison
Zt =102.3 km
Zt =93.1 km

15. CAMS/BRAMS 1st comparison
Zt = km
Zt = km

16. Comparison with meteor profiles

18. Amplitude (a.u.)
Time (sec)
Blackman filter

19. CAMS/BRAMS more accurate comparison
Check that the time corresponding to (e.g.) Half Maximum Power is close to the theoretical time due to specular reflection

20. Determination of peak power
Ppeak-under =
Mc Kinley (1961)

21. Gains of the Tx / Rx antennas 
GR(,)
Credit : A. Martinez Picar

22. Calibration of peak power : the BRAMS calibrator

23. Calibration of peak power
« Calibrated » value by determining the amplitude of the calibrator signal
Ppeak-under in Watts

24. Limitations
Mc Kinley’s formula is strictly valid for underdense meteor echoes. Quid for overdense ones or even those with intermediate electron line densities?
Most antennas were tilted at that time, which means that their gain GR(,) is not very well constrained in the direction to the reflection point.
For the polarisation factor, we can tentatively take ½ (assuming we emit a circularly polarised wave, which is not exactly the case)
We have also to check the stability of the calibrator over time
Not all stations were working nominally at that time (problems with receiver, no calibrator everywhere, mismatch of antennas, etc…)

25. Electron line densities
We obtain the linear electron line density  in different points along the meteoroid path

26. Comparison with simulations
First, with a relatively simple model such as the one from Vondrak et al (2008). Matlab code available from VKI
V and  given by CAMS
m assumed with typical values (unless other information available)
Only unknown remains the mass

27. Comparison with simulations
q is the ionisation rate (in e-/m3)
General idea :
Run the model for several « reasonable » values of the initial mass. Each model produces a profile of q as a function of the distance along the meteoroid path
Pick up the value of the mass that minimizes (in least square sense) the difference between simulated values and values obtained from BRAMS data
For that, establish link between q and 

28. Perspectives
Correct the existing codes to analyze BRAMS/CAMS data and make them robust
Run the Matlab codes for the Vondrak model and pick up the best solution
Use more recent data from 4/5 October 2018 – 522 orbits
Present these results at EGU meeting – Vienna – 7-12 April 2019
Publish the results
Explore other possibilites to decrease the aforementioned limitations

29. Thank you