Transcript here - Brams

BRAMS : status and perspectives
Hervé Lamy
Belgian Institute for Space Aeronomy (BISA)
STCE Workshop : radio and optical observations of meteors
30/01/2014
Outline of the talk
1. Status of the BRAMS network
2. Current activites
3. Perspectives
STCE Workshop : radio and optical observations of meteors
30/01/2014
The BRAMS team
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Hervé Lamy
Sylvain Ranvier
Emmanuel Gamby
Stijn Calders
Michel Anciaux
Johan De Keyser
 Antonio Martinez Picar (ROB)
 + support from mechanical/electronic workshop at BISA
 + regular help from Pierre Ernotte, Felix Verbelen, Jean-Louis Rault
STCE Workshop : radio and optical observations of meteors
30/01/2014
Meteor scatter observations
2 advantages on optical observations
STCE Workshop : radio and optical observations of meteors
30/01/2014
Reflection is specular
Information on only one point of the trajectory
STCE Workshop : radio and optical observations of meteors
30/01/2014
Observability of a given meteor
STCE Workshop : radio and optical observations of meteors
30/01/2014
Status of the BRAMS network
STCE Workshop : radio and optical observations of meteors
30/01/2014
BRAMS: current status
25 receiving stations
Distance E-R <<
Tx in Dourbes
STCE Workshop : radio and optical observations of meteors
30/01/2014
The beacon in Dourbes
 49.97 MHz
 150 W
 pure sine wave
 circular polarisation
STCE Workshop : radio and optical observations of meteors
30/01/2014
Typical receiving station
AGC off
RG213
Spectrum Lab
STCE Workshop : radio and optical observations of meteors
30/01/2014
Material
Gent
STCE Workshop : radio and optical observations of meteors
30/01/2014
Material
Behringer U-Control UCA222
STCE Workshop : radio and optical observations of meteors
30/01/2014
Synchronisation of stations with GPS
NMEA
PPS
Sampling frequency  22 KHz
STCE Workshop : radio and optical observations of meteors
30/01/2014
Recording of the data
• Signals are recorded locally on the PC with Spectrum Lab. Configuration
file of this software is provided by BISA.
• Data are recorded in audio WAV format with 2 channels (stereo mode)
• Sampling frequency  22 KHz in order to decode the NMEA
• Every day at 2 AM, a script developed at BISA allows to decode
automatically the GPS data from the day before. The decoded signal is
added to the file as a « chunk ».
• Before that, the signal from the receiver is decimated by a factor to
reach an effective sampling frequency of 5512 Hz.
• One new file with data is created every 5 mins. Size of one file is  3
MB. 288 files per day   1 GB of data / day
• Data are stored locally for  1 mnth and then sent to BISA via USB sticks
for archiving.
STCE Workshop : radio and optical observations of meteors
30/01/2014
f = 200 Hz
Spectrograms
Code to generate spectrograms
Nb samples = 16384
Covering factor = 90%
STCE Workshop : radio and optical observations of meteors
30/01/2014
Spectrograms
Overdense meteor echo (+ head echo)
STCE Workshop : radio and optical observations of meteors
30/01/2014
Spectrograms
« Epsilon » meteor echo (Draconides 2011)
STCE Workshop : radio and optical observations of meteors
30/01/2014
BRAMS viewer
STCE Workshop : radio and optical observations of meteors
30/01/2014
Current activities
STCE Workshop : radio and optical observations of meteors
30/01/2014
Automatic counting
• Many meteor applications require an accurate counting of the number
of meteors detected per unit time (e.g. observability function, fluxes of
meteors, activity of a meteor shower, etc..)
• Since the BRAMS network provides every day around 25 x 288 WAV files
 need for an efficient algorithm for automatic counting of meteor
echoes
• So far  method mostly based on recognition of specific shapes in the
spectrogram considered as an image. Developed mainly by P. Ernotte
and some of his students.
• Works quite well for underdense meteor echoes
• Not so well for overdense meteor echoes / epsilon echoes
STCE Workshop : radio and optical observations of meteors
30/01/2014
Automatic counting
Main problems :
• Intersection of plane
echoes
• Difficult to define a
specific shape for
overdense/epsilon
echoes
2 detection methods for underdense / overdense meteor echoes
STCE Workshop : radio and optical observations of meteors
30/01/2014
Manual counting
• Mandatory to assess the accuracy of the automatic detection
method
• Online tool developed by Emmanuel Gamby
STCE Workshop : radio and optical observations of meteors
30/01/2014
Interferometric station in Humain
Jones et al (1998)
STCE Workshop : radio and optical observations of meteors
30/01/2014
Interferometric station in Humain
STCE Workshop : radio and optical observations of meteors
30/01/2014
Interferometric station in Humain
STCE Workshop : radio and optical observations of meteors
30/01/2014
Calibration & antenna characterization
• Determination of the 3D radiation pattern of the antenna in order to obtain
G(,)
• At least for the interferometer, Tx in Dourbes and crossed Yagi in BEUCCL (but
hopefully also for other BRAMS stations)
• Two complementary studies :
1. software simulations
2. campaign of measurements to validate the simulations and estimate the
impact of the immediate environment of the antennas
STCE Workshop : radio and optical observations of meteors
30/01/2014
Calibration & antenna characterization
Single Yagi antenna pointing vertically
Horizontal
Vertical
STCE Workshop : radio and optical observations of meteors
30/01/2014
Calibration & antenna characterization
Tx antenna
Horizontal
Vertical
STCE Workshop : radio and optical observations of meteors
30/01/2014
Calibration & antenna characterization
In situ measurements
Payload : source of known amplitude (see next slides)
Must fly in the far-field region of the antenna (  2D2/  3m)
STCE Workshop : radio and optical observations of meteors
30/01/2014
Calibrator for BRAMS
Purpose :
1. Check the gain and frequency offset/drift at every station
2. Identify sudden jumps or anomalous behaviour of a station
3. Calibrate the gain and phase differences at the interferometer
and at BEUCCL. In particular, the phase offset of each receiver
is susceptible to jumps after a power recycle (receivers not
phase locked to a common reference).
STCE Workshop : radio and optical observations of meteors
30/01/2014
Calibrator for BRAMS
Method :
1. Signal of a known frequency and amplitude fed into
the front end
2. Frequency is in the useable band so that the signal can
be monitored continuously while gathering echo data
3. Small USB powered unit, frequency and amplitude are
programmable and can be adjusted as needed (10 dB
range, 1Hz steps)
4. For the phase calibration, the same signal is fed to
multiple receivers at the same time. The phase
difference between the receiving chains can then
monitored.
STCE Workshop : radio and optical observations of meteors
30/01/2014
Perspectives
STCE Workshop : radio and optical observations of meteors
30/01/2014
Meteor radar in Dourbes
• Goal : comparison of
fluxes measured by a
back scatter and
forward scatter system
• Status : preliminary
design done, material
procured, work should
start this year …
STCE Workshop : radio and optical observations of meteors
30/01/2014
Trajectory reconstruction
R2
• Softwares need to be developed & tested
• Applicable mostly to underdense meteors
• Need for a dense and extended network
STCE Workshop : radio and optical observations of meteors
30/01/2014
Trajectory reconstruction
• Importance of adding optical cameras to reconstruct trajectories of
bright objects
• These bright objects correspond to overdense meteor echoes for which
the specularity condition is not strictly followed
• It will be important to compare quality of reconstruction methods
STCE Workshop : radio and optical observations of meteors
30/01/2014
Extension of the BRAMS network
STCE Workshop : radio and optical observations of meteors
30/01/2014
Le site web BRAMS
brams.aeronomie.be
STCE Workshop : radio and optical observations of meteors
30/01/2014