brams : status and perspectives

STCE Workshop : radio and optical observations of meteors 30/01/2014

BRAMS : status and perspectives

Hervé LamyBelgian Institute for Space Aeronomy (BISA)


Outline of the talk

1. Status of the BRAMS network

2. Current activites

3. Perspectives


The BRAMS team

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


Meteor scatter observations

2 advantages on optical observations


Reflection is specular

Information on only one point of the trajectory


Observability of a given meteor


Status of the BRAMS networkStatus of the BRAMS network


BRAMS: current status

Tx in Dourbes

25 receiving stations

Distance E-R <<


The beacon in Dourbes

49.97 MHz

150 W

pure sine wave

circular polarisation


Typical receiving stationAGC off

RG213

Spectrum Lab


Material

Gent


Material

Behringer U-Control UCA222


Synchronisation of stations with GPS

Sampling frequency 22 KHz

PPSNMEA


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.


Spectrograms

Code to generate spectrograms Nb samples = 16384Covering factor = 90%

f =

200

Hz


Spectrograms

Overdense meteor echo (+ head echo)


Spectrograms

« Epsilon » meteor echo (Draconides 2011)


BRAMS viewer


Current activitiesCurrent activities


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


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


Manual counting• Mandatory to assess the accuracy of the automatic detection

method• Online tool developed by Emmanuel Gamby


Interferometric station in HumainInterferometric station in Humain

Jones et al (1998)


Interferometric station in HumainInterferometric station in Humain


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 simulations2. campaign of measurements to validate the simulations and estimate the

impact of the immediate environment of the antennas



Single Yagi antenna pointing vertically

Horizontal Vertical



Tx antenna

Horizontal Vertical



In situ measurements

Payload : source of known amplitude (see next slides)Must fly in the far-field region of the antenna ( 2D2/ 3m)


Calibrator for BRAMS

Purpose :

1. Check the gain and frequency offset/drift at every station2. Identify sudden jumps or anomalous behaviour of a station3. 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).


Calibrator for BRAMS

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.

Method :


PerspectivesPerspectives


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 …


Trajectory reconstruction

R2

• Softwares need to be developed & tested• Applicable mostly to underdense meteors• Need for a dense and extended network


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


Extension of the BRAMS network


Le site web BRAMS

brams.aeronomie.be

brams : status and perspectives

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