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Strong signal on June 14th at 20:43:40 UT


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I would be interested to know if anyone captured the very strong echo I received on  my systems on on June 14th at 20:43:40 UT. 

2019-06-14_204340.jpg.8463d47392b057d0bcd22b77263fab1e.jpg

I think these are possibly the strongest I have ever recorded with SNRs of 78, 69 and 81 respectively.  It may well have been quite local to me in Hayfield, Derbyshire.

Mike

 

 

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To put the SNR in context here is the distribution of counts in given 1dB S NR bins for the three systems so far this month.   The higher the SNR the stronger the echo. The SNRs represent one event in over 10000 so far this month.

 Distribution.jpg.574f143857144e5d951102261a78e1d7.jpg

Edited by Geminids
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I didn't capture that one Mike, but my detector has been offline for a little while as we have been doing some work on the house.

Two thoughts come to mind: the Doppler shift on the head echo is slow.  Although it's difficult to estimate the absolute velocity from a single observation, in this case, you can clearly see the phase switching every two seconds in the head echo indicating its frequency is changing slowly relative to time.  That is suggestive of a slow entry, meaning space debris rather than meteoric.

The second thought is related to the location.  You speculate it being close to your site, presumably due to the very strong signal to noise ratio.  However, if near overhead, your antenna would be unlikely to see a common volume to the GRAVES radar.  More likely, is that is is south of the radar and the debris has a large mass resulting in an intense ionisation.  This could build upon an already elevated ionisation of the E-layer that occurs during summer months and in particular late June/early July.  Sporadic -E propagation can be seeded by incoming debris or meteors and perhaps this was the case here?

Richard

Edited by BiggarDigger
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Thanks for the negative report Richard - I hope your system is back on line soon.  I take your point about the slow head echo - a quick measurement of the spectrogram gives a duration for the visible part on the bottom plot of just over two seconds and 255 Hz shift (124Hz/s slope), and as you say, it is not easy to get velocity from this, particularly because the location of the object is unkown.  

I must admit I haven't considered space junk before.  Like you, the geometry is not right here to get meteor scatter from anything other than the GRAVES rear/side lobes.  But of course if it's higher altitude it could be junk.     Are  any studies conducted into such debris detection and has anyone here and are there any confirmed recordings?   How can junk and meteor events be differentiated?  Would one have expected space junk to spin and hence generated glint?   

I have three antennas: one points towards Dijon  as shown below.  The idea of the vertically pointing Red and Green channels is to provide better sky coverage than traditional orientation.

2065978704_VHFAntennas2019.jpg.5c326c833f32f1d357d40dc65bf55f07.jpg

 

21 hours ago, BiggarDigger said:

  More likely, is that is is south of the radar and the debris has a large mass resulting in an intense ionisation.  This could build upon an already elevated ionisation of the E-layer that occurs during summer months and in particular late June/early July.  Sporadic -E propagation can be seeded by incoming debris or meteors and perhaps this was the case here?

It is a pity you were off-line at the time because a comparative record would have been interesting and might have  confirmed or otherwise your suggestions .

... but there may be other observers out there who did capture something?


Mike

PS New here - does the Notify me of replies work? Also sorry about the image size - is there a way to make them smaller.

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That's a nice antenna array Mike and could be very useful in calculating further parameters, if you can correlate against known trajectories and signals, for example from the ISS.  The orthogonal and vertical components may yield interesting results.  The mast head preamps will assist with weak signal detection and overcome feeder loss too.

I was perhaps not specific enough when I mentioned space debris.  In this context, I meant incoming man-made orbital debris entering the upper atmosphere at sub orbital velocities of maybe 7km/s as opposed to a meteor which may have a velocity of 40-60km/s.

The radar itself is presumably tracking orbital parameters of objects in low earth orbit and hence looking for direct scattering off the object itself, such as we might see on the ISS from the radar.  However, your observation has a head echo suggestive of low incoming velocity followed by an ionisation trail, which would be reasonable to ascribe to an over-dense field in the ionosphere caused by the incoming object.  In other-words, I suspect it was in the atmosphere at a similar altitude to a meteor and not in orbit.  Due to the slow Doppler it was possibly not meteroic, but a de-orbiting piece of orbital debris.  I don't have the mathematics to verify, but it seems reasonable that the SNR would be related to the intensity of the ionisation and that in turn related to the velocity and mass of the object.

All other things being equal, the intensity of the SNR and slow Doppler suggest to me that it was a high mass object entering the upper atmosphere at sub orbital speeds rather than a grain of sand entering at cosmic speeds.

Of course, I could be wrong and would be interested in hearing opinions.

Richard

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The antenna array, Richard, was intended for the very purpose of measuring more parameters.  One of the thins I do is keep my eye out for reported video meteors with trajectory data that coincide with my radio observations.  The system is still in development and I have much more to learn about it - and then to interpret meteor results. I have yet to do a top to bottom calibration of the channels.  

The head echo and subsequent long, spectrally wide trail is typical of meteors.  Having thought about it overnight, by the same reasoning that , in the higher UK latitudes GRAVES meteor scatter cannot be observed because it is below the radio horizon, if the "junk" was entering south of Dijon, the subsequent E-layer ionization would also be below the horizon.

The fact that there are seasonal variations in E-layer ionization which is enhanced by the passage of meteors could lead to an interesting study of any annual differences in maximum signal levels on a statistical basis (distributions such as in my earlier post perhaps). There was a paper recently on "Solar cycle variation in radio meteor rates" , by MJ Campbell-Brown, MNRAS 000,  10 (2019) in a similar vein.

As for the relative strength and proximity to me, again I have been thinking about this and remembered some rough calculations I did using the radar equation and a "standard" radar cross target and fixed height so that just the slant ranges from Dijon to object and object to me were the only variables.  This yield a variation in signal level, the highest being over Dijon and me and the dip of -7dB in the middle.

I will try to think about the variations in "angular" velocity and trajectory to see how that changes the frequency slope.

 

Mike

Edited by Geminids
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49 minutes ago, Geminids said:

The antenna array, Richard, was intended for the very purpose of measuring more parameters.  One of the thins I do is keep my eye out for reported video meteors with trajectory data that coincide with my radio observations.  The system is still in development and I have much more to learn about it - and then to interpret meteor results. I have yet to do a top to bottom calibration of the channels.  

Excellent!  It will be fascinating to hear about the development of the system and your correlations against video detected meteors, particularly those over central England versus central or southern France.  Have you been able to measure or calibrate the radiation pattern of the array - that will yield important additional information to feed into the cross channel correlations.

 

Quote

The head echo and subsequent long, spectrally wide trail is typical of meteors. 

It is similar, but my contention is that the head echo exhibits a slow speed Doppler shift, suggestive of a sub-orbital speed object as opposed to a meteor travelling perhaps an order of magnitude faster.  Do the majority of your captures exhibit a slow head echo?

In general, one needs to be a bit careful about the spectral interpretation.  With not much resolution presented in the time domain, the trace looks like it has the typical spikes occurring at the phase switching points of the radar array.  These spikes are I believe caused by aliasing in the FFT employed in Spectrum Lab.  As such, they do not necessarily tell us much about the nature of the object causing the echo or scattering, but indicate the response of the FFT to a high amplitude impulsive change when the transmitter phased array switches.  Their presence however does indicate a scattering or reflective medium at a stationary point in the sky, as one would expect from an over dense plasma field.

Certainly, I agree that it is an outlier on the SNR chart that you present, and all the more fascinating to understand what it may be.

Richard

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On 01/07/2019 at 11:36, BiggarDigger said:

Have you been able to measure or calibrate the radiation pattern of the array - that will yield important additional information to feed into the cross channel correlations.

As a start I have asked the antenna designer if he can give me detailed radition patterns, naturally he is reluctant to share his commercial design models.  I also, over a number of years been interested in the moon bounce signals and can extract them digitally from the rest of the events.  I am confident I have the Lunar position and Doppler at given time that correlate with my recordings.  At the moment this is part of the general filtering of non-meteor data but it will bear further analysis when i get the time.  The plots below show real (meteor) event frequencies in a month period in blue and Moon bounce as downward red lines.  Horizontal lines in red are interference lines. As can be seen the detection of th moon bounce signal is different between the three antennas.  Signal strength of Moon bounce will also be analysed.

1666862891_AccRej2019-07-01_142259.jpg.a8f60847b5622047bf4f5be4df4a18ec.jpg

On 01/07/2019 at 11:36, BiggarDigger said:

It is similar, but my contention is that the head echo exhibits a slow speed Doppler shift, suggestive of a sub-orbital speed object as opposed to a meteor travelling perhaps an order of magnitude faster.  Do the majority of your captures exhibit a slow head echo?

I think that a slow speed Doppler shift >may< depend on the trajectory: for example a very shallow angle would allow a long time in the ionosphere and coupled with an appropriate direction over land .... as I said I will try some numbers ... 

No the majority of my head echoes are much shorter.  (I am still working on head echo capture techniques)

On 01/07/2019 at 11:36, BiggarDigger said:

In general, one needs to be a bit careful about the spectral interpretation.  With not much resolution presented in the time domain, the trace looks like it has the typical spikes occurring at the phase switching points of the radar array. 

Actually looking at my own spectrorams in more detail, I must agree with the spikes being Spectrum Lab's FFT artefacts rather than the other type of long duration event that I get where there appear to be a range of frequencies of similar signal strength.

On 01/07/2019 at 11:36, BiggarDigger said:

Certainly, I agree that it is an outlier on the SNR chart that you present, and all the more fascinating to understand what it may be

Yes.  Thanks for the thought provoking discussion.

Mike

 

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