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Old 20-04-2022, 11:48 AM
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sheeny (Al)
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Here is a summary of how I interpret the infrasound signals of meteors. Consider it like any hypothesis - it's the best I have till it's disproved.


Al.
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Last edited by sheeny; 10-05-2022 at 12:55 PM. Reason: typo
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  #22  
Old 23-04-2022, 10:39 AM
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Stumbled on this example of a two particle negative phase (entry to atmosphere past the observer) meteor while browse the helicorder looking for interesting signals.


Al.
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  #23  
Old 24-04-2022, 02:28 PM
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graham.hobart (Graham stevens)
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infrasound

Hi Sheeny, this is an interesting thread and one close to my heart having some raspberry pi seismometers and a home built meteor cam based on the GMN ones. Would be great to chat via email for more info.
My gmail is
grashie69@gmail.com
cheers graham
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  #24  
Old 07-05-2022, 12:00 PM
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sheeny (Al)
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Back from a week away, I decided to do a little infrasound survey on last night's data to see if i could detect a change in the rate of meteors after eta Aqu rose. Looks to have detected the change, though obviously not all meteors that would have been visible were detected and identified by infrasound.


To do the survey, I set up a 0.5 to 10 Hz bandpass filter and scanned the helicorder about 15 to 20 minutes at a time looking for sharp spikes that are balanced above and below zero. I noted the minute these occurred then came back later to zoom in to the wave form and check that it is an N wave (or multiple), check it's not a seismic triggered event and to classify the meteor type. No analysis of the meteor signal was done to split component particles if any were evident.


I need to set the camera up for some star trails and capture some meteor images to correlate to the infrasound.


Al.
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Last edited by sheeny; 07-05-2022 at 12:06 PM. Reason: Afterthought
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  #25  
Old 08-05-2022, 08:13 AM
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Image to Infrasound Correlation

With the eta Aquarid shower in progress I decided to get up early this morning and shoot some meteors in a timelapse and use the time from each photo identify the corresponding infrasound signal.


Sounds simple in a statement like that.


It turned out more difficult than expected, and partly due to some rookie mistakes.


When I first hatched the idea of using timelapse images to time the meteors, I envisaged the camera pointing to the zenith. Intuitively I knew that was the best place for it because that's where the meteors will be closest.


However, it's the eta Aquarids... so I pointed the camera at the radiant and didn't think about it enough.


Next time... at the zenith!


Not capturing at the zenith increases the distance to the captured meteor. This does a couple of things:
  1. it decreases the signal strength;
  2. it increases the sound travel time, and so increases the timing errors.
The session was successful in that I learned what to do next time. It was not very successful for correlating the meteor images to the infrasound however. The signals were too faint, so mired in noise if detectable at all, and the compound errors from estimating expected heights of meteors and angle of elevation meant it was not possible to clearly identify a single signal that corresponded to the image.


It was also the first time I shot a timelapse with this camera and used the in camera timelapse function rather than my old interval timer dongle. Not being familiar meant the interval between shots was longer than intended. I thought I set 1s between shots but it ended up much longer, so with 15s exposures about 50% of time was missed. I only realised how much by comparing the gap in a satellite trail between shots. Noise reduction was turned off so that wasn't the culprit.



Attached are my calcs and notes. I didn't get as many shots as I intended as the clouds rolled in, but it was better than nothing.


Al.
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Last edited by sheeny; 08-05-2022 at 08:20 AM. Reason: afterthought
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  #26  
Old 10-05-2022, 11:48 AM
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Another Complex Meteor

Too cloudy to try to correlate photos to infrasound again this morning, so had a look through the data and found this one that looked interesting.


Resolved it to 3 particles but I suspect there's possible 4 in it, but the final particle signal was pretty weak, so maybe it was real or maybe not.


Al.
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