Ambient Noise Temography.

[Jim in Idaho]

6 hours ago, jasong said:

Not me, but Jim has. 🙂

Separately, a company I sold a project to did some resistivity surveys with a professional contractor. That contractor ended up unfortunately lighting a part of the mountain face on fire in doing so a few years back! 

Still seems to me, Jason, you'd have to know the strength of each random noise source, relative to each other in order to make it work. GPS works because the initial impulses are at a set timing, so distance can be calculated at the receiver, and compared to other delays to calculate angle, and thus location. I'm still not confident that random noise would be much use, other than having the random noise from a known source location. Even then you'd have to know the comparative distance from each sensor in order to determine the earth effects. Maybe I'm just slow....LOL

Jim

[jasong]

31 minutes ago, Jim in Idaho said:

Still seems to me, Jason, you'd have to know the strength of each random noise source, relative to each other in order to make it work. GPS works because the initial impulses are at a set timing, so distance can be calculated at the receiver, and compared to other delays to calculate angle, and thus location. I'm still not confident that random noise would be much use, other than having the random noise from a known source location. Even then you'd have to know the comparative distance from each sensor in order to determine the earth effects. Maybe I'm just slow....LOL

Jim

With seismic (sonic) waves, you are not measuring strength but instead measuring the difference in time between refracted or reflected impulse that results from the interface of two different materials which two different velocities which sound travels through it. You are measuring the initial impulse (thump) time and then measuring the arrival time at an array of sensors. It's all time based. Signal strength is only really relevant insomuch as you want a strong enough impulse to travel as deep as you need it to go., but how strong it is is mostly irrelevant for the imaging other than max depth. Time is the critical measurement to generate subsurface imagery.

Velocity is a function of time, distance between sensors is known, thus time is your critical measurement for this type of subsurface imaging.

Similarly like with sound waves - EM waves travel through different rock types with different velocities. So you can use very similar methods to measure time and determine where formations change. In this case it's not so much the density of the rock (as with sound waves) as it is the conductivity changes in the rock.

Seismic refractometers (oilfield thumpers) are an example of the sound wave frequency range tools.

GPR are an example of the EM frequency range tools. 

They both work similarly, by measuring time in order to generate the imaging. 

Anyways, if one really needs signal strength, you just measure the magnitude of the incident signal at t=0. Then the strength of the reflect signal at t=t2. 

[Jim in Idaho]

1 hour ago, jasong said:

With seismic (sonic) waves, you are not measuring strength but instead measuring the refracted or reflected impulse that results from the interface of two different materials which two different velocities which sound travels through it. You are measuring the initial impulse (thump) time and then measuring the arrival time at an array of sensors. It's all time based. Signal strength is only really relevant insomuch as you want a strong enough impulse to travel as deep as you need it to go., but how strong it is is mostly irrelevant. 

Velocity is a function of time, distance between sensors is known, thus time is your critical measurement for this type of subsurface imaging.

Similarly like with sound waves - EM waves travel through different rock types with different velocities. So you can use very similar methods to measure time and determine where formations change. In this case it's not so much the density of the rock (as with sound waves) as it is the conductivity changes in the rock.

Seismic refractometers (oilfield thumpers) are an example of the sound wave frequency range tools.

GPR are an example of the EM frequency range tools. 

There are cool tricks to measure the speed of light (actually, less) over tiny distances, since it's often faster than 1 cycle of the fastest CPU's. These can be employed cheaply, and is one reason why I've been saying GPR needn't be as expensive as people think it is, it can be a "pro-sumer" level tool, and it already is decreasing in price rapidly plus has drone mounted options. 

Yeah...after watching the entire video, I'm starting to understand how this works. Mainly, it's a ton of calculations to arrive at a conclusion. I can also see why it's now becoming useful. Wasn't that long ago we didn't have enough computing power and speed to do the calculations. It' sort of a play on the old "give typewriters to a large enough group of monkeys and eventually they'll produce the works of Shakespeare"....LOL, but with hi-tech enhancements. Hoping all is well with you, Jason. I imagine, like me, you're itching to get out prospecting again.

Jim

[jasong]

Haha yeah I've been chasing all sorts of blind leads in the lower elevations. We didn't get much snow this winter, so I was able to do a bit of exploring so far. But we just got 2 days of snow so I'm back stuck at home pounding on my keyboard now. 🙂

The ore body prospecting invention I was proposing was something between seismic refraction and GPR: ULF/ELF ambient military transmissions (they can travel through the ocean/around the world/into ground). Depth similar to sound waves, but imaging via conductive interface changes like GPR. But not imaging in fine resolution like GPR, just looking for large scale conductive interface refraction (metallic ore bodies, buried lithium reserves, large salt domes, oil reservoirs, aquifer mapping, etc) as with seismic. Sorta both, but neither. 

I'm guessing this is what this company is using along with a combo of other sources for finer/deeper occurences when the noise exists? No idea though. 

[Jim in Idaho]

Ya know, the Navy did a whole bunch of research at their facility on Priest Lake here in Idaho. They were researching ultra-low frequency communications for talking to the world-wide fleet of submarines. Would be interesting to know what freq they ended up using, assuming you didn't go to jail for espionage...LOL. I thought your idea was pretty good. If I remember right it was useful for more than precious metals, too....like rare earth minerals. I'm still getting into the data-logging with the two box deep detectors, though haven't been doing anything with it since winter set in. Start of March we had bare ground, and then the blizzard hit and we had 15" of snow, and single digit temps, and that took care of spring for awhile. Snow's gone now, but we got 3/4" in one squall this morning. I think I'm still looking at a month before I can do much. Looking forward to at least one trip to your area this summer.

Jim

 

[HardPack]

Ambient noise implies to me a low level constant sonic source as to a shorter duration thumper or earthquake seismic wave. The ANT cross section I have seen online indicate gross fault offset or dip change with depth.
My question is with a ANT surface array in place combined with a constant sonic signal would the cross section imagine resolution improve over time with repeated timed measurements to a level to be able to pick out the contact between different rock formations?