Understanding GRAVES Meteor Events

[PhotoGav]

As the title suggests, I would like to try and understand what the waterfall display of GRAVES reflections can tell me about the meteor that caused it. Or was it even a meteor...??!

Here are a number of event screen shots.

These are the 'normal' ones - what do the various shapes, durations and brightnesses say about the meteors?

 

 

And then some weirder ones:

 

 

I look forward to hearing how to identify the 'reflection zoo'!!

 

Finally, is it appropriate to correlate these two as being the same meteor?

 

Thanks,

Gav.

[wxsatuser]

The last image of the group has a satellite reflection.

[andrew s]

If they drift left or right then that is due to the doppler shift as they move away or towards you.

Regards Andrew 

[PhotoGav]

14 hours ago, wxsatuser said:

The last image of the group has a satellite reflection.

Good stuff, thank you. I thought that was the case. It will be interesting to catch the ISS passing by one day!

 

14 hours ago, andrew s said:

If they drift left or right then that is due to the doppler shift as they move away or towards you.

Regards Andrew 

Ah, interesting, thank you. I thought that Doppler shift was correlated to frequency change, dropping in Hz as the meteor slows down in the atmosphere, hence the events with the ‘tails’ moving down the waterfall and the bright blob at the end. So much to learn!

[andrew s]

Mixture of both in fact. Regards Andrew 

[Geminids]

18 hours ago, PhotoGav said:

As the title suggests, I would like to try and understand what the waterfall display of GRAVES reflections can tell me about the meteor that caused it. Or was it even a meteor...??!

Actually Gav, there are many of us with the same ambition of trying to understand  waterfall or spectrogram displays.  The links to video or still images is tenuous, not suprisingly as the direct light captured on camera is totally different to GRAVES scatter from ionisation trails.  Head echoes such as the one on your 01:15:01 spectrogram can tell us something, but with a lot of effort.  In the spectrogram following, the event looks like an underdense meteor.  The longer duration events may be the specualar trail or sometimes longer lasting ionisation drifting in upper atmosphere winds.

2 hours ago, PhotoGav said:

. It will be interesting to catch the ISS passing by one day!

If you capture more ISS passes on your radio you may be interested in sharing them with this group here https://radiometeordetection.org/radioproject

Edited December 5, 2020 by Geminids

[PhotoGav]

6 minutes ago, Geminids said:

Actually Gav, there are many of us with the same ambition of trying to understand  waterfall or spectrogram displays.  The links to video or still images is tenuous, not suprisingly as the direct light captured on camera is totally different to GRAVES scatter from ionisation trails.  Head echoes such as the one on your 01:15:01 spectrogram can tell us something, but with a lot of effort.  In the spectrogram following, the event looks like an underdense meteor.  The longer duration events may be the specualar trail or sometimes longer lasting ionisation drifting in upper atmosphere winds.

If you capture more ISS passes on your radio you may be interested in sharing them with this group here https://radiometeordetection.org/radioproject

Thank you, that is all interesting and helpful. Hopefully I might be able to contribute some useful data to the Radio Meteor Detection project in time, extending the contributor area in the south!

On another question, if I may - does the angle of elevation of the aerial matter that much? I have another thread asking about this, but thought I would seize you while I have you! Is it ok if the aerial is level rather than raised to my theoretical optimum of 17°?

[Tomatobro]

22 hours ago, PhotoGav said:

Finally, is it appropriate to correlate these two as being the same meteor?

I put that question at the end of a talk by an expert  and was told no. The ones we detect are a long way off.  Something to do with the distance between us and the radar site and the reflection angle as I recall.

[PhotoGav]

33 minutes ago, Tomatobro said:

I put that question at the end of a talk by an expert  and was told no. The ones we detect are a long way off.  Something to do with the distance between us and the radar site and the reflection angle as I recall.

Interesting, thank you, but what a shame!

[Geminids]

22 hours ago, PhotoGav said:

Finally, is it appropriate to correlate these two as being the same meteor?

Although the times are similar, it actually depends on where the meteor was.  Do you get tajectory details from you voisual observations?  

21 minutes ago, Tomatobro said:

Something to do with the distance between us and the radar site and the reflection angle as I recall.

This is essentially correct - it does depend on a bit of geometry;  for seeing what is called specular scatter from the trail it is neccessary for the path of the meteor to touch an ellipse with foci at GRAVES and your location. Thus, the geometry is unique to your location and it is not likely applicable to other locations.  However, it is possible for anyone to see a head echo, if strong enough.  There are also the really long duration events that are "non-specular" and are not dependendent on the geometry - so can be seen in many locations.  You may want to look at this https://www.imo.net/observations/methods/radio-observation/intro/ which explains some of the ins and outs.

 

4 hours ago, PhotoGav said:

On another question, if I may - does the angle of elevation of the aerial matter that much? I have another thread asking about this, but thought I would seize you while I have you! Is it ok if the aerial is level rather than raised to my theoretical optimum of 17°?

Unless you have a very high gain antenna with a very narrow beam-width, it will not make too much difference.  

[PhotoGav]

Thank you @Geminids.

No, there is no trajectory info from the all sky camera, though the meteor in the image above was a Leonid, so moving from east to west. 

Thank you for that link, I will enjoy reading and learning, there’s lots of good stuff there.

I don’t know what the details are for the antenna I have - how would I find those things out?

[The Admiral]

From my primitive investigations explaining the traces does seem to be quite involved. There are a number of documents which I have referred to along the way, which you might find interesting. I'll list them at the end.

I'm sure that you've heard this before, but the Graves transmitter beams in a Southerly direction from it location near Dijon at an altitude of between  ~15° and ~40°. If the meteors detected are at around 100km high then this will give a distance of between 120km and 325km to its South, assuming simple line of sight. Something like this:

On a map, this looks something like:

The transmitter doesn't broadcast to the whole of the zone simultaneously, but switches cyclically between zones of azimuth. However, there has been some recent discussion on here about how it is possible for those in Scotland, for example, to be able to receive scatter traces even though they are beyond line of sight. As a result there has been some speculation that the antenna may also produce a 'backfire' beam which scatters off meteors nearer to home.

The reflected frequency is Doppler shifted as a result of the moving meteor (head echo) and the ionized tail left behind. If my understanding is correct the meteor itself doesn't really slow down, but loses energy through ablation. So although it is easy to think of the Doppler shift is as a result of slowing down, as I originally did, but it is more complicated than that. Have a look at the following documents, which I hope will be of some interest, if you haven't already that is .

Ian

Detection_of_meteors_by_RADAR.pdf

Graves-Echo-english.pdf

Detecting Orbiting Objects.pdf

Meteor Detection using SDR.pdf

Radar Echoes from Space DK5EC.pdf

Radio Doppler fromForward-Scatter Head Echoes.pdf

[PhotoGav]

@The Admiral, that’s great, thank you Ian. I’ve seen some of these documents, but not all. Plenty of research reading there. I agree, it’s not simple! 

[wxsatuser]

Try these as well

http://www.ars-electromagnetica.de/robs/

https://ea4eoz.blogspot.com/2015/05/determining-radiant-of-meteor-using.html

[The Admiral]

4 hours ago, wxsatuser said:

Try these as well

http://www.ars-electromagnetica.de/robs/

https://ea4eoz.blogspot.com/2015/05/determining-radiant-of-meteor-using.html

Good stuff! Thanks.

Ian

[johnb]

Hi so we are attempting to match Video \ Radio events and its not quite as simple as you would think, to aid us we are mapping the radio sky using known ISS passes (and correcting for location and altitude)

If you look at this map https://radiometeordetection.org/radiomap

you will see we are making progress, when we have more data we will then look for video events in our area of interest and see if we have any corresponding radio events 

for more info do have a look here: https://radiometeordetection.org/radioproject

Kind Regards

John B

[PhotoGav]

Hi John, that is fascinating, well done for attempting the mapping project and for the excellent results so far. It seems that the meteors we detect with the GRAVES frequency here in the UK are generally occurring in the atmosphere above France somewhere, which are unlikely to be seen visually from southern England. Is that correct?

[Geminids]

21 hours ago, PhotoGav said:

 It seems that the meteors we detect with the GRAVES frequency here in the UK are generally occurring in the atmosphere above France somewhere, which are unlikely to be seen visually from southern England. Is that correct?

Actually, the ISS exercise we are conducting shows where the GRAVES signal is reflected by the ISS.  We project the ground location back to the altitudes where the "radar beam" could meet a meteor and scatter.  The meteor radio map is therefore only an indication of regions with the potential to have meteor scatter.  You will understand that these results are dependent on ISS orbit - it only goes as far N as about London latitudes which work back to the meteor areas of Northern France latitudes.  Video match could be supplied by French video networks eg BOAM.   If we have other satellites with large reflecting surfaces that travel further North we will expand out field of video/radio match possibly to UK video coverage. 

[PhotoGav]

@johnb - I think that I have just detected an ISS pass:

 

 

That is certainly the strongest satellite signal that I have seen so far and there was a pass today from my location as follows:

12:36:48 W 10˚  ->  12:40:04 SSW 47˚  ->  12:43:19 SE 10˚

 

Please let me know if it would be useful for your project and if so, how to go about adding observations.

 

[PhotoGav]

Looking through my data, I have found some more probable ISS events.

This is a little earlier from the same 18-12-20, 12:40 pass:

 

And one from the 07:50 pass this morning:

 

And finally, a noisy one from the 13:27 pass yesterday 17-12-20:

 

The ISS 'ugly' orbit is obviously just in the right patch of sky right now, so no doubt more events to come.

 

[johnb]

so Gav, contributions are indeed welcome, have you read https://radiometeordetection.org/radioproject - PM me and I will send more info

 

Kind Regards

John B