What's the minimum to start meteor detecting?

[Stub Mandrel]

1 hour ago, The Admiral said:

Hmm, it might be, but I'm not so sure it is. I wouldn't have thought it would be at constant frequency, which is perhaps a little too high.

No, it doesn't show  on the RF trace, look on the left had side of the AF trace at bottom right.

There's a very faint diagonal line dropping from 1100Hz to 700Hz. The AF timescale is a bit more expanded and covers about 30 seconds to about 10:31:30 when the ISS would be heading away from Graves, I watched it moved from above to below.

[SteveNickolls]

There seems a nice amount of activity going on at the moment from the daylight Arietid shower. Only switched on a few minutes and 12 detected already.

Cheers,
Steve

[The Admiral]

5 minutes ago, Stub Mandrel said:

No, it doesn't show  on the RF trace, look on the left had side of the AF trace at bottom right.

There's a very faint diagonal line dropping from 1100Hz to 700Hz. The AF timescale is a bit more expanded and covers about 30 seconds to about 10:31:30 when the ISS would be heading away from Graves, I watched it moved from above to below.

Ah that, OK, gotcha! It does look like it .

Ian

[SteveNickolls]

Watching ISS Tracker the ISS will be in a good orbit next two times around for possibly picking it up using GRAVES.

Cheers,
Steve

[SteveNickolls]

Coming in thick and fast, 28 now.

 

[The Admiral]

5 minutes ago, SteveNickolls said:

Watching ISS Tracker the ISS will be in a good orbit next two times around for possibly picking it up using GRAVES.

Cheers,
Steve

Do they all pass to the South of Dijon? I'm a bit confused by thd output of 'Heavens Above'.

Ian

[SteveNickolls]

18 minutes ago, The Admiral said:

Do they all pass to the South of Dijon? I'm a bit confused by thd output of 'Heavens Above'.

The next pass ought to go over Dijon and Italy then the following is across Central Spain. There's a chance to detect something on the next pass but the following ought to be more likely.

So far this hour there's been 29 detections of meteors in 23 minutes, the last one was a longer one, around a couple of seconds in duration-

Cheers,
Steve

[Stub Mandrel]

2 minutes ago, SteveNickolls said:

29 detections of meteors in 23 minutes

Can't say I'm getting that many, or that long, but I am seeing blits every few minutes.

Hopefully a proper connector will arrive in tomorrow's post and that will improve sensitivity.

Do you use any sort of filter or amp before the SDR module?

[SteveNickolls]

Hi Neil,

I have just the FunCube Pro+ dongle connected into the pc via USB, nothing more. 

Regards,
Steve

[The Admiral]

52 minutes ago, SteveNickolls said:

Hi Neil,

I have just the FunCube Pro+ dongle connected into the pc via USB, nothing more. 

Regards,
Steve

Same here, no antenna amp or anything. The FCP+ does have built in filters though, which IIRC are automatically set. 

Ian

[SteveNickolls]

Well that ISS pass over left a decent trail, I'll post the screen grabs together and work out the coordinates over which the ISS flew when I get back as i have to pop out in a bit. I might miss the next pass over unfortunately.

ISS 19.6.2018.docx

Cheers,
Steve

[SteveNickolls]

Well that indicates a initial detection of the ISS near the place called La Chapelle-Montligeon, France to over the Adriatic between Pescara, Italy and Dubrovnik, Southern Croatia. I'm intrigued to again detect the ISS outside the expected 180 degrees sweep East-South-West. Can't imagine it would be another satellite coincidence?

Cheers,
Steve

[The Admiral]

I switched over from SDR to SL, and after a few hiccups (it's a long time since I last used it and I had to do a bit of re-learning!), got that going, but there now seems to be very little meteor activity. I've switched back to SDR just to see if it makes any difference. Hmm, still quiet.

Ian

[The Admiral]

Very quiet, here's one just come in. I'd say we're back to normal background rate now.

Ian

[The Admiral]

Ah, now here's a more interesting one, which shows the initial strike trail well. Is it picking up?

Ian

[Stub Mandrel]

Didmn't pick up that last ISS pass at all, or if I did it was so faint I may have been deluding myself ?

I was seeing them between 5 and 5:30 at about one every minute or two, mostly small but one or two quite good ones. I'll post a pic of the best.

[Stub Mandrel]

Progress, at a snail's pace!

There is a pre-programmed meteor detection USR setting in Spectrum Lab, used with the 'virtual cable' (and HDSDR sending its audio down the 'cable') I got this:

OK so now I can talk to Spectrum Lab. I will have to try and get it set p with a detection script. One problem I have is I can here hits in HDSDR, but SL is silent. It was making noises on the RF setting. I have utterly no idea what to tweak, an some of teh controls seem completely random.

[Stub Mandrel]

Holy cow batman! The sound of this nearly knocked me off my stool! It actually looked like a meteor flying across the screen. Did anyone else get it?

[Stub Mandrel]

I was asked for an explanation on another forum. This is my guess informed by various documents, any comments:

The big blob is probably a stationary, or just moving with the atmosphere, cloud/trail of ionisation left behind by the meteor. I haven't fully calibrated the receiver, but it's about 200Hz out so that would move the column close to the radar frequency of 143.050 MHz showing little doppler shift*.

The streak is probably a return from the intense (moving) patch of ionisation at the location of the meteor itself.

If the blob represents a velocity near zero, the trace suggests the meteor moves towards and then away from the receiver.

But... the Arietid meteor radiant was just below the horizon a bit beyond north-west. This suggests it came in from the direction of the north west heading south east, and where the line crosses the blob would represent the point of its closest approach.

The frequency  drop is 1,450 Hz (distance between two ends of the trail).

This makes the line of sight velocity change about 3,143 metres per second (online calculator!)

3.1kms/sec seems fast, but the Arietids arrive with a velocity of about 39 km/s.

A bit of trig gives an angle of about five degrees, OK that's rough and ready and assumes we see the full trace but does suggest the meteor was observed nearly from the side, providing a sensible explanation for the doppler shift going through zero.

[The Admiral]

The meaning of these traces is to my mind a bit of a uncertain. My understanding is that the bright spot, and with longer lived affairs, the bright vertical line, is due to the reflection from the fully ionised column of air, which is relatively static. With long lived events, you sometimes see lines emanating from that bright line, and these are believed to be the result of bits of the meteor's nucleus being explosively ejected. All that is fine. But as to the origin of the 'first strike' line, well, I'm not sure. Perceived wisdom, as I understand it, is that we would not have the sensitivity to actually see the reflection from the meteor head itself, but I'm not so sure. I'm also not sure that the FFT is actually fast enough to resolve the motion of a meteor head itself. Both Steve and I have been pondering this and we've no conclusion.

The picture is a little complicated so far as Doppler shift is concerned because there are two shifts, the first being the shift due to the movement between the meteor and Graves, and the second being due to the movement between the meteor and the receiver. For the essentially stationary ionisation column this is largely irrelevant, but would have implications for the origin of the 'initial strike'. Does your 'on-line' calculator take this into account? The paper cited below doesn't appear to, surprisingly, which is incorrect.

Have you looked at this article by Dr David Morgan of the BAA? I imagine you have.

Detection_of_meteors_by_RADAR.pdf

Ian

 

[Stub Mandrel]

Yes I've read the BAA paper about three times the last week!

My understanding is that the near-horizontal lines sloping down to lower frequencies are not the meteor itself but the short-lived but intense ball of ionisation around it - what we see as a 'fireball' and the near vertical smudges are what we see (rarely, I've only seen one once) as the persistent column as you describe.

I imagine it as the meteor making a bright patch of ionisation that rips across the sky, leaving a less intense but more persistent cylinder behind it.

I thin it's exactly the same as what your image here shows, but your waterfall drops from top to bottom so the slope is reversed:

[The Admiral]

But isn't the "ball of ionisation around the meteor"  the same as the meteor head, which is really what I meant? Actually, the longer lived columns are not that rare during meteor showers, particularly with the Persids IIRC.

Neil, here's another, deeper, paper I've just dug up from history . I need to refresh my mind on this!

Speculation on Meteor Echoes 2012.pdf

I can't find that on t'internet now though.

Cheers, Ian

[Stub Mandrel]

It doesn't help that most of the 'scholarly' stuff is about pulsed radar.

Us amateurs using phased arrays and doppler radar are in another league ?

[Stub Mandrel]

That paper is quite heavy (a shame we can't find the author - the properties give the name collingwood), but I think the following applies to my recording, I added the emphasis:

 

Does the RCS of a moving plate (plasma front) scatter enough signal to be observed? What
would a CW radar return look like from the situation described in this model?
A great deal will depend on the geometry of the observation ie the location of the radar
source, receiver and the direction of the trail. Without a mathematical description of the
geometry we cannot answer this question in detail. However it should be possible to make
clear some points.
Given sufficient illuminating power from a radar source at some general angle from the
meteor vector – and given sufficient plasma front RCS in the direction of the receiver, one
would expect to see a return signal with a changing Doppler shift with time as the LOS
resolved component changes with the geometry. If the meteor is slowing down, this
resolved velocity component would further decrease with time. (However many of the
plasma generation models in the literature assume a meteor particle has a near constant
velocity until its mass is exhausted).
Would there be a geometrical arrangement of radar source, receiver and meteor track
where the LOS velocity would decrease with time – as is sometimes observed?
If we take it that the initial return signal from the meteor would show some type of Doppler
shift depending on geometry, what might we see at later times? The moving plasma front
will at some point cease to develop (due to meteor mass being exhausted being too low in
the atmosphere) and a Doppler signal will disappear. However the stationary plasma trail
may still exist (lasting for 1 second or more) and a strong signal may be expected from this
large conducting object with a high RCS. It will though have little or no Doppler shift. High
altitude winds may impose some bulk movement on the trail, or it may break up due to
shear winds – and in such cases some small Doppler shift will be imposed on the signal.
The foregoing suggests that returned signals may sometime have two clear components
(ignoring wind effects for the moment) – a high Doppler weak signal component and a
stronger signal with little or no Doppler shift. In measurements made by the author of
meteor reflections from the Graves Radar, returns with these characteristics have
commonly been seen.

 

 

In the article this figure is used to deduce a meteor seen side on so it approaches and then recedes:

 

 

[The Admiral]

I don't know who the author is either. I need to give this paper some thought!!

Ian

Edit. On the original word document it shows the author as 'DAVID'. That could be anything.

Edit 2. I wonder if this is David Morgan? On p26 in the 2nd para, it states "In ref 18 we analyse....."  Ref 18 is a paper by Morgan.