Meteor detecting

Having a gigantic birdcage on your roof should be a status symbol. Ideally it should glow in the dark. My neighbours are so unimaginative. They even think owning a lathe is eccentric. Ho hum.

Hello Muzzer,

Point taken, I must be more careful about my prefixes!

Andrew.

Hmm... that mast is only 4m high, not 32 feet. It's stood upright for about 15 years with a weather station on top with similar windage...

If your lathe is eccentric may I suggest balancing the chunk or wedging the baseplate?

Good point Dave and as you observe, light pollution is a problem, but back then and in such an isolated location with zero local lighting the sparkling magnificence was still pretty impressive with a milky way to die for!

Rik

For OPTUS D1 and Home and Away and Neighbours?

I have to ask: Why do you want or indeed need to detect meteors? It sounds about as useful as George Merryweather's Tempest Prognosticator. If the meteor is big enough you will definitely know if it has become a nearby meteorite

John

It sounds a fun thing to try.

I did some research into meteor burst communications a while back - trying to maximize the data throughput - because as the ionization trail dies away the reflectivity, and hence the link capacity, diminishes.

The problem with meteors as a means of communication is that they are not regular throughout the day. The earth mops up lots more meteors at 6am local time than it does at 6pm where only those travelling faster than the earth can graze the ionosphere.

Jon

Bernard Lovell, using ex-radar equipment, at Jodrell Bank in 1946, was the first to discover and detect meteors during the day.

Geoff

Why sit in a workshop making useless objects when you could be out in the fresh air?

Edited By Neil Wyatt on 19/06/2018 17:34:20

Funnily enough although that's generally true, at the moment the current shower is the 'Daylight Arietids' which comes roughly from the direction of the sun and over the last half hour I was picking up one every minute or two.

How about this for a biggy?

The long line is the meteor slowing down, the big 'flash' is the ionisation cloud. Probably...

Neil

Can you describe what we are looking at here please?

I've been wondering what it is you are receiving. From what I’ve read here I guess it is the signal from the source being reflected of the ionisation trail. But what are you capturing? The reflected broadcast FM signal, the doppler shifted CW component or both?

As your last note suggests ‘slowing down’ so I guess you are getting the doppler shift in the X axis but is Y amplitude and the ‘big flash’ being the stronger reflected signal from the ionisation cloud? As I also guess the display is aggregated over time how is that represented?

If you are getting the doppler shifted signal can you determine the velocity of the vector in the axis towards the receiver?

Pete

I was going to let Neil explain, but I had this idea...

This is a HDSR display, generated in the computer. It is listening to Graves radar, on 143.0488 MHz, which it can not hear, but when a meteor passes, the Graves signal is reflected, leaving a trail on the 'Waterfall' display.

Imagine a loom weaving cloth, which slowly lengthens, as the shuttle passes back & forth through the 'shed' formed by the raising and lowering of the alternate threads. If something is trapped in there, a lump will form, and be incorporated into the cloth. This is like a waterfall display.

Geoff

Geoff

Thanks; a bit early in the day?

I get the concept of a waterfall display. So Y is time, with current time at the bottom and and X is frequency rising from left to right.

Pete

(edited  I've just realised I can zoom the image)

Edited By Doubletop on 20/06/2018 05:37:02

The main signal has a doppler shift of 900Hz and (using an online calculator) a velocity of ~950m/sec or 2125mph (towards Neils house)

Pete

( could well be wrong....)

Early? I'm often conscious, if not compos mentis, earlye in the morning.

Geoff

To try and answer multiple posts.

As Geoff says it's a 'waterfall' display but falling upwards, so the oldest data is at the top.

Frequency is the x-axis and brightness/colour shows signal strength.

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.

It's a good detection as most tracks only show one or other of these features, and typically much smaller.

What confuses me is that 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 Atlantic heading south east, and where the line crosses the blob would represent the point of its closest approach. When the ISS passes over you see exactly the same sort of frequency shift through zero, although it changes much more gradually.

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 (yes 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 fromxwwuio the side, providing a sensible explanation for the doppler shift going through zero.

Neil

*the Graves frequency is 143,050,000. Tuning to 143,048,800 and listening to the upper sideband means that an unshifted signal will be at 143,050,00-143,048,800 = 1,200Hz.

The fact I'm getting it at about 930Hz suggests the tuning calibration is 270Hz out, but measurements of terrestrial staions suggests.

Neil

Thanks; I'm getting to understand this so some degree, helped when I found I could zoom the image and read the detail.

Surely you can't use the total frequency shift as the indication of velocity as it represents closing and receding velocities? You can only use the deviation from the fundamental +ve and -ve

Alternatively could it be the case that the range of the crossing is so great that the closing velocity is relatively minimal and the bright cluster, on the fundamental, is really the main signal with minimal doppler shift. As your array has a wide beamwidth the cluster exits for all the time it is within your beamwidth. Indicated by the height of the cluster (Y). Then the frequency shifts being some sort of spectral noise or harmonics that exist for the duration of the event being at the same time as main cluster? Basically, for any point in time during the event there is a large return on the fundamental plus a secondary signal that sweeps +ve to -ve as the event progresses. It would be good to see a plot with an expanded (Y) axis.

In the case of the ISS, as it is so close, there would be doppler shift so it would also be interesting to see a plot of the ISS to see what the ISS spectrum looks like for comparison.

Pete