I see these double inverted booms in north San Diego county on the RS&Boom unit. Any ideas about the origin?
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If that was at my place, Iād say it was a dog going through the doggie doors. ;o) We have two doggy doors - one from the sun room (where my S&B is) into the mud room and one from the mud room to outside.
Hereās an example of a dog coming into the mud room (small positive spike first) then into the sun room (larger positive spike second).
Your first spike looks like door opening into the room where the Boom is (positive pressure first) and the second looks like a door that swing open outwards from the room where the Boom is (negative pressure first).
Suggest you try some local sources like doors and windows and see if you can recreate it. If Dataview refresh time is too slow to be sure of correlating the signal to the action (due to comms lag), SWARM is good as itās just local network.
#EDIT: Thinking a bit more about it, they might not be doors into the room where the S&B is. Both your spikes appear to have a similar detail to the first of my example spikes which is in an adjacent room. There are more oscillations and more higher frequencies in the spike entering the same room as the S&B.
Al.
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Dear Sheeny,
Many thanks for your observations. Just to clarify, I have added a tube that pokes through the wall of my instrument room to get isolated signals from outside of the house. I do see some fine looking meteor signals. We are in an area that does get artillery booms from Camp Pendelton, but these are not common at the moment. I have been stumped by the time delay and the inverse symmetry of the signals. What the heck physical process could cause this and has anyone seen similar signals? This is frankly why I bought the unit, to discover the unknown! I was thinking, perhaps the second pulse is either an echo or has passed through an alternative propagation pathā¦
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GāDay David,
I think it would be highly unlikely the echo would be of similar strength to the direct signal. Reflections do change some wave characteristics but Iām not sure that phase of a pressure wave is one of them. Maybe someone else can confirm? I would expect a reflected positive pressure wave to also be positive, but I might be wrongā¦
Have you identified/eliminated all possible local infrasound pressure sources? I realise that with a tube the signal should be dominated by the pressure at the open end but stranger things can happen. ;o)
Are all the signals the same phase, shape, strength and period between spikes? SWARM is very good for accurate timing of events to check the period between spikes (to thousandths of a second).
Iād love to see some of your possible meteor signals. Maybe I should try piping the Boom port outside for mineā¦
Al.
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Hi Al,
I have barely explored all possible infrasound sources. Here is a typical meteor signal, seen fairly often. Agreed, both signals are about the same amplitude, not common for an echo. I think about transmission lines, which echo very differently for open or closed (shorted) ends.
There is a ShakeBoom user south of me in Poway, CA (S3774) and I wonder if he sees similar things.
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In fact I did check S3774 and found a similar double trace. This is from about 20 miles south of me i Poway, CA.
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GāDay David,
Nice possible meteor trace!
I think you have the makings of an excellent investigation to get your teeth into especially if you can see similar signals on S3774.
Iād suggest correlating signals with the same phase and time between spikes and work out distances from the time differences. Hopefully differences in amplitude might suggest some clues then (i.e. either confirm distances or not, etc). If the signals donāt have the same phase and time between spikes, then they arenāt the same event, and also if the time between the signals is greater than the sound travel time between the 2 Booms.
Interesting!
Al.
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A very interesting discussion daviddrake, sheeny; lots of prompts to investigate!
I have to start looking more closely for these typical meteor echoes signals, I wonder how many I didnāt notice in the past.
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Looking back for about a week, most of these double booms are coming +/- a couple of hours around local noon. No fireworks going off at these times. I donāt think it electrical noise, due to its coherent appearance and odd symmetry. Still a mystery!
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You mention that you are located in north San Diego county - could these signals be sonic booms from military aircraft flying off the coast? Under normal circumstances, military aircraft are not permitted to fly supersonic over land, but may practice supersonic flight over the ocean. The signals appear to have the classic āN-waveā of a sonic boom. Especially since the signals are appearing within a specific time period during the day, could the double peaks be from two aircraft practicing supersonic flight together off the coast?
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FINALLY ! An answer ! The āmysteriousā double booms are caused by the door swing into and out of the instrument room. I forgot the external sensing tube is really measuring the gauge pressure between the unit and the input pipe. The pipe pressure stayed constant, but the room pressure was influenced by the door swing. Idiot me for not realizing this earlier. Sorry for the spurious confusion, but many thanks for the thoughtful responses. Again, the Raspberry Shake team causes useful neurons to fire! Many thanks, Team Shake.
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Excellent. Now you know what they areā¦ just when I was about the settle in with the popcorn too to see what these were! o)
Al.
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Thatās why the community is a great place to brainstorm a bit! A very interesting discussion indeed.
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Running both ports to the outside should fix the problem, no?
Ken
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GāDay Ken,
They already are. The single port on the outside of the Boom is connected to the dP sensor by two tubes - one of which has the mechanical filter. The dP is developed across the mechanical filter.
Al.
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OK - so what is the mechanism transmitting the ādoor boomsā into the RBoom?
Is it because the tube is long and flexible? In that case, the solution would be to pipe it up with something like a natural gas line - rigid pipe.
Or is the building itself acting as a sounding board? That might be harder to remedy.
I know when our clothes washing machine shakes the house, it registers on RShake and also on RBoom which is some 100 feet away from the house.
here is an example of that:
I think you would have to slam the door of the house rather hard for it to show up though.
Maybe I will try that later ā¦
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I think most likely itās because the tube is long and flexible.
The building acting as a sounding board is not impossible either. Think about how an acoustic guitar body works.
I thought I posts a list of possible mechanismsā¦ maybe itās in another threadā¦
Yes I moved my RS&B from the house out to the observatory to get away from the cultural noise in the house, only to find that the only things I got away from were the doors opening and closing in HDF. The washing machine, dryer, doors opening and closing, even computer printer still transmitted seismicly to the observatory 15m from the house. When I had comms problems in the observatory I moved it back to the house. The doors are a minor problem in HDF really. The important thing is to know what they are and not confuse them with other signals.
Al.
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Hereās that post with some of the ideas I had for why it might be happening:
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