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BiggarDigger

Meteor detection: path from Scotland to GRAVES

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Nope, didn't see anything on that traverse either Steve.

The other thing of course is that for the ISS at 412km altitude, the intersection distances from Graves become 490km to 1500km*. So wouldn't you be even less likely to see them Richard?

Ian

Edit. Assuming a flat earth!

Edited by The Admiral

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Thanks Richard for your comments. This is certainly something together we can gather more data for in the coming days. Having said that I won't be up to follow the next fly over later tonight.

Cheers,
Steve

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Not a peep here from the pass at 21:41 either.  The weather is foul outside and it's noticeable how that affects my background meteoric detection rates too.

Yes, with the ISS much higher, incident angles will be very high and any reflections difficult to detect.  Ideally a known object orbiting in very low Earth orbit transiting North West to South East will help determine where my meteor reflections are coming from.  Trouble is, I don't think there is much that operates at such low altitude. ?

Richard

(Exiting stage left for tonight to collect my son from work)

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Here's one I did for my location, green is approx lower meteor altitude,  yellow upper (and have tried to give a '3D' representation of the volume between the two. Purple is the ISS altitude. This is roughly based on the known elevation and azimuth angles for the GRAVES beam (obviously there may be back lobes and the forward beam may extend more to the North than the abrupt E-W line shown.  The ISS sector is truncated to the West based on the approximate reception pattern on my antenna.

radar.png.7666a5998e7d23aad3be0937277676bc.png

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It's good to see the ISS zone in relation to the meteor zone. These should be easily seen above the horizon from our Southerly regions, but at those distances my sensitivity may be limiting.

Ian

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Thanks IanL for this pictorial representation of ranges and volumes, very helpful. Regarding the purple region I have detected the ISS when above Sardinia and in the middle of the Adriatic Sea and my location being somewhat further North to you yields a good approximation to the region you have produced. ?

Regards,
Steve 

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I just captured the ISS south of the radar site at 19:13, close to my extreme range:

image.thumb.png.dee0d825e995fc53a16f7426c0baddb1.png

Though the next pass at 20:49 may be more useful as it runs North of the site.

I'm not sure if I'll be available for that pass though because family commitments may take priority tonight.

Richard

 

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Hi Richard thanks for the post.

Hope you can be available to record any detection later but understand family commitments. I will have my equipment ready to record any of the next pass tonight.

Cheers,
Steve

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I managed to squeak away to the study for half an hour and may have a very weak and tenuous detection at 20:48.  One pulse between 20:48:25 and 20:48:27 falling from 1100 to 900 Hz  and a second pulse at 20:48:32 to 20:48:34 falling from 500 to 300 Hz.  Very weak and not at all certain, but it looks like there's something there on the SDR# waterfall plot too.

849222702_weakISS26thSept20-48.thumb.png.73e128be8f47d36be95213488690ae89.png

 

Earlier I drew a rough and ready diagram earlier of what I expect my meteoric reflecting region, limited at 90km altitude.   It's mostly north of the radar site, with some areas include din the radiation pattern to the west:

651473196_Meteorreflectionrange.png.7802cd2f1531732d41bbf14740cc5277.png

(back to family for the evening now.....)

Richard

 

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On 18/09/2018 at 14:00, BiggarDigger said:

Historical tracking puts the ISS over the Bay of Biscay

I've tracked the ISS at both ends of the Mediterranean.

I saw a slide of triangulations of Graves detections from the UK/Scandinavia and virtually all of them were behind the radar.

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22 hours ago, Stub Mandrel said:

I saw a slide of triangulations of Graves detections from the UK/Scandinavia and virtually all of them were behind the radar.

Interesting Neil, do you have a copy of that you could share with us?

 

I was just catching up on the lounge postings and happened to see a strong satellite response on my Spectrum Lab screen at 20:17 (19:17 UTC):

image.thumb.png.765638432b7af3f1a65506487e291222.png

The ISS was over Asia at the time and a very quick look through the Heavens Above site doesn't show anything in there list of obvious candidates that could have generated the trace.  The zero Doppler shift point is at 19:17:47 UTC.  Any ideas what that and where that may have been?

Meantime, I'm hoping to try track the 21:30 BST transit.

Richard

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15 minutes ago, BiggarDigger said:

Interesting Neil, do you have a copy of that you could share with us?

Sadly not, it was shown at a presentation at our club - the one that got me into this silly meteor business!

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Success! I think......

I've just had a decent detection off the 23:10BST pass, while the ISS was over northern France, north of the radar site.

The downside is that I messed up the screen grab and only just caught part of the trace before it scrolled of Spectrum Lab display.  The frequency scale starts at 0Hz with major ticks at 200Hz, so the trace just disappearing off screen to the left is at 1100Hz and 800Hz.  My zero Doppler shift position is at 1200Hz:

 

image.png.bbb67f39c9c179a4c93000922f914a28.png

This is a much stronger trace than the tenuous detection yesterday evening.  I'm annoyed that I messed up the screen grab, because there was about 10 seconds of trace before this screen grab, where the signal was slightly positively shifted.  The trace at 23:10:45 is entering negative Doppler shift, hence moving away form me, which corresponds nicely with the track of that pass:

image.png.3de13d1e02332f96f40765ccfabbd286.png

Together with anecdotal evidence, these measurements suggest a significant rear lobe radiation at high enough angles from GRAVES to paint the sky in an area through which my detected meteors are passing, i.e Northern France.  That makes me much happier (relieved?) that I'm not imagining things and also adds further info for mid and high latitude sites for antenna location and angles.

I'll continue to monitor passes, especially for similar tracks to this, plus I'm searching various ephemera databases to look at what the earlier detection this evening was, but I'm quite happy now!

Richard

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12 hours ago, BiggarDigger said:

Any ideas what that and where that may have been?

Perhaps Stellarium can be your friend here. If you base it on Dijon and look for any passes? Mine shows an Ariane 40 R/B around, and a couple of other satellites, but it might not be up to date. Would need to check out their details.

Ian

Edited by The Admiral
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9 hours ago, BiggarDigger said:

I've just had a decent detection off the 23:10BST pass, while the ISS was over northern France, north of the radar site.

Very interesting Richard. Thanks for posting.

Ian

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A casual goggle has found me this report which seems to indicate that the Graves radar illuminated volume is significantly larger than just the quoted Southerly one, sufficient to allow correlation of the radar reflections with visual identification of meteors towards the South in the UK.

Correlation of Video and Graves Detections.pdf

Ian

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Excellent stuff Ian. I suspect that's related to the work I saw an example of.

I notice that meteor detections rarely show the strong 'pulsation' seen with ISS detections. I suspect ISS is being picked up by the direct beam which scans through four quadrants. I think the backscatter from Graves is no so directional and therefore a more consistent signal.

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10 minutes ago, Stub Mandrel said:

I notice that meteor detections rarely show the strong 'pulsation' seen with ISS detections.

Well I suppose too that the ISS is a much 'cleaner' signal and therefore any pulsations are easier to see than the 'mess' you get with meteors. Also, BiggarDigger's detection above of the ISS North (only just) of Dijon does show some pulsation. It's hard to draw conclusions I think about the exact nature of this 'rearward' irradiation field, and certainly the French military are not going to give too much away. :wink2:

Ian

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59 minutes ago, The Admiral said:

A casual goggle has found me this report which seems to indicate that the Graves radar illuminated volume is significantly larger than just the quoted Southerly one, sufficient to allow correlation of the radar reflections with visual identification of meteors towards the South in the UK.

Correlation of Video and Graves Detections.pdf

Ian

That's a really good find Ian.  By correlating radio and video detections, it  presents clear evidence of meteoric reflections from north of the radar site that I believe I've been detecting on my horizon.  

 

29 minutes ago, The Admiral said:

It's hard to draw conclusions I think about the exact nature of this 'rearward' irradiation field, and certainly the French military are not going to give too much away. :wink2:

Ian

I think this is a very telling observation though.  There appears to be a field to the north of Dijon which is large and strong to generate reflections off meteor trails to make them detectable at my site, but I think the geographical extent and strength of that field can only be an informed guess at at present.  

I suspect, but it is only a suspicion, that the rear lobes may not by design, but are significant enough to be calibrated into the system.  This is because reflections off debris from the rear lobes would lead to significant "noise" in the system if not taken into account.  If it were a deliberate radiation pattern, it would make more sense to build the site using a circular array, but the photographs of the site don't really support that.....but I must stress this is purely speculation.

Richard

 

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I didn't see anything on the 21:26 pass, but I got a good long trace on the 23:05 pass last night. This was the track (centred on Dijon so the times shown are BST+1).

1254941584_ISSTrackrefDijon.jpg.45f47c8bf41d133958c977ebb45091d5.jpg

 

I didn't see anything until 23:02:50 BST, which is due West of Dijon, and the reception ceased by 23:05:20BST, which on the track for my area corresponds to where the 10° circle is.

Here's my trace (I hope it shows OK when clicked on).

170408836_2018-09-2923-05compo-1.thumb.jpg.a70eb105dc2ea29aa39be28fcc76cda7.jpg

Note for this trace I set the frequency to 143.047MHz, so the 'zero' is at 3kHz (as confirmed by the occasional meteor recording), which was reached at about 23:03:20BST . You'll also see that at around 23:04:17 the trace got to ~0Hz and then I started to plot the image, so the trace starts to rise again.

Ian

Edited by The Admiral
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Interestingly, the maximum altitude reached at Dijon was 60° at 23:04:11 BST, so was 'theoretically' above the recognized radar beam profile. My signal dropped out around then before reappearing a little later. I'm not sure if this was due to the system's response when the signal and local oscillator are almost the same, or whether it was due to it being above the radar beam.

Ian

Edit. I've just looked at the system response using GB3VHF When I reduce the difference frequency, and there doesn't appear to be much difference. So, I conclude that the drop out is most likely due to the ISS moving into the Graves radar shadow.

Edited by The Admiral
Further thoughts.

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Sorry, I've been a bit tied up the last couple of days as we have family visiting.

If you are tuned using Upper Sideband to a centre frequency 3KHz below the centre frequency of the radar the zero Doppler shift point should be at 3Khz in your audio spectrum, I think.  This may not necessarily indicate the point at which the ISS is closest to the receiver or transmitter however as the Doppler shift is a combination of the two.  That said, the pass you caught would have been closest to you at around 23:02BST and getting further away (reducing in frequency) thereafter.  However, the signal reaching the ISS would have been increasing in frequency until around just after 23:04 after which it would have been decreasing.

The different Doppler rates do not cancel each other out however, so I think you can get some pretty strange looking frequency traces.

In any case, I would have expected at 60° above the radar site it would have been out of the major lobes and the amount of signal scatter from the ISS would have been significantly reduced.

I'll probably be unavailable again this evening, but if there favourable passes to the North of the radar early next week, I'll see if I can capture some more data.

Richard

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I'm no expert on doppler, but I understand that bot velocity relative to the source and velocity relative to the receiver affect the frequency.

The shift is zero when the velocity relative to both cancels out. so a body travelling on a line parallel to transmitter and receiver would make no shift (like bouncing the signal off a static wall along the track).

A body moving across from one side to the other of a line joining the two would show a decrease in frequency as it crosses the line joining them, being at transmission frequency as it crosses the line.

While traces that drop past the transmission frequency are not uncommon, I don't see many that are all below it (i.e. whole track heading away from the line joining me to Graves). I can't explain this.

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