(meteorobs) Fw: [baa-rag] Radio (meteor?) Reflection 201301071248

[Felix Verbelen]

Hello Jay,

Thank you for your mail.
At first sight there seems to be at least a "scale" problem...

Observing our 49.99 and 49.97 MHz beacons from a distance of 
respectively 120 and 90 km, almost permanently reflections of numerous 
jet planes are registered.
The planes can of course come/go in different directions, but taking 
into account the beacon's radiation diagram, we know that best 
reflections are obtained when the plane follows a course which brings it 
over the beacon.
For these commercial plane reflections, the SpecLab registrations show a 
maximum doppler of some 80 Hz.
Since a commercial jet plane travels at a velocity of some 800 km/h 
(this is 222 meters/second), we would obtain very roughly a velocity of 
some 10/80*222 (m/s) = 27 m/s, thus some 100 km/h in the case of 
Jean-Louis' "corkscrew shapes" with a 10 Hz doppler.

Kind regards.

Felix



Jay Salsburg schreef op 12/01/2014 00:28:
> Let me express some facts to help get our brains wrapped around what is being recorded from forward scatter Meteor RADAR beacons.
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> First; Forward scatter, by its very nature, is not back scatter. Back Scatter RADAR retro-reflects RADAR energy directly off the moving object, back to the transmitter/receiver. The Doppler frequency is generated by mixing the returned RADAR energy with the Transmitter to produce a difference velocity frequency. The received velocity is a product of the RADAR Frequency, the speed of light, and the cosine of the angle of movement in relation to the illuminating RADAR transmitter. Unless the object is moving directly toward or away from the transmitter with zero angle, or, in other words, is moving parallel, the velocity will always be less than parallel movement, which will be times the cosine of the angle of movement.
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> Second; RADAR Doppler velocity for parallel movement can be easily computed. For a 50 MHz RADAR Beacon, the Velocity constant = 0.1491 Hz per MPH.
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> Third; The technical requirements for receiving Forward scatter RADAR energy is, by its very nature, not receiving Doppler RADAR Energy anywhere near parallel to the RADAR Transmitter. In fact the angle of incidence may be quit shallow, rendering the Doppler Frequency offset from the transmitter frequency very low. Together with the low frequency of the beacon, the Doppler offset is very low; only a few Hertz.
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> Forth; For Backscatter RADAR, the receiver must use Carrier Wave or Sideband reception, necessitating an offset frequency for recording and display purposes. By subtracting this offset frequency from the received Doppler, an actual relative velocity is realized.
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> Observing the first image in the Rauly.pdf document referenced below, the offset Carrier is centered around 590 Hz. The higher frequency is near 600 Hz. 600-590 is 10. 10 times 0.1491 Hz per MPH = 1.5 MPH. It is entirely possible to closely compute the actual angle of incident of the movement from the transmitter. Let us arbitrarily choose 30 Degrees. This means the reflection is 60 degrees or 0.5 of the recorded velocity which equals 3 MPH. There may also be movement at near right angle to the transmitter further reducing the relative velocity.
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> This very low velocity of only a few MPH is what is seen in the corkscrew recordings.
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> Jay Salsburg
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> From: Jean-L. RAULT [mailto:f6agr at orange.fr]
> Sent: Wednesday, January 08, 2014 1:43 AM
> To: radiometeoren at vvs.be
> Subject: [radiometeoren] Fwd: Re: Fw: [baa-rag] Radio (meteor?) Reflection 201301071248 [1 Attachment]
>
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> -------- Message original --------
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> Sujet:
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> Re: [radiometeoren] Fw: [baa-rag] Radio (meteor?) Reflection 201301071248 [1 Attachment]
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> Date :
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> Tue, 07 Jan 2014 18:54:11 +0000
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> De :
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> Jean-L. RAULT  <mailto:f6agr at orange.fr> <f6agr at orange.fr>
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> Répondre à :
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> f6agr at orange.fr
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> Pour :
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> g4csd at yahoo.co.uk
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> Paul
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> This is a typical "corkscrew shape" echo which appears from time to time.  See for example http://www.imo.net/imc2010/talks/Rault.pdf for a meteor echoes signatures gallery.
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> I personally don't know any good paper on the meteor echoes signatures.  This is a domain which does not seem to be investigated by professionnal searchers at the moment.
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> Amateurs have a lot to do in this domain !
>
> Regards
>
> Jean-Louis Rault
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