Quote:
Originally Posted by Aurificus
Consider a large, wide, dark, deep, fast flowing river. We wish to find the rock that is just bigger than the others and will snag the bottom of our boat.
We could take numerous measurements of the rivers current at points above and below and all across the stream and hope to find the infintesimal change in Kilo litres/per min caused by the obstruction of the rock.
Or... we could sprinkle lots of tiny leaves on the surface upstream and look for the one that stops or circles in the "eddy" caused by the Rock.
Dont let the big stuff cloud your view of the small stuff
Aurificus
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This is precisely the problem with the theory you presented. The big stuff is clouding the view of the small stuff that the detector is looking for.
In the analogy you presented, the large rock would represent the degree of variations in the thermal energy supplied by the sun (due to shadows and surface moisture). And what we are looking for is not a large rock, but a very small pebble which is buried amongst the large rocks. ie: The shadows and damp spots in the soil cause large deviations and gradients in the solar energy supplied. The buried metal object represents only a very small fraction of a percent of the thermal gradients seen at the surface above it. In fact, any thermal gradient derived from the presence of the buried metal receives it's energy from the same non-uniform larger gradients above at the surface, after it is conducted downwards as heat. So we are basically starting with a non-uniform energy input to energize the buried metal before trying to locate it.
Since we are looking to sense a very small thermal anomaly where the buried metal object is, the problem becomes one of signal to noise ratio. In other words, what is to stop the large energy anomalies caused from shadows cast on the surface from absorbing the pulsed IR LED energy instead of the faint anomaly from a metal coin buried 10 cm below the surface? After all, the variation of thermal energy caused by the surface shadows and moisture is at least several hundreds of times stronger than the variations in thermal energy caused by a buried metal object.
Then there is still the problem of the divergence of the beam of an IR LED. Esteban did not use a collimator to focus into a narrow beam. He used a plain IR LED with the attached factory lens, which typically has a 40 degree cone of illumination. This suggests that at 10 meters, the IR LED is illuminating a spot of 6 meters diameter. A deviation in the power pulsed to the LED could be caused by absorption anywhere within that 6 meter diameter circle. If the theory presented is correct (an anomaly of thermal gradient is causing the small variation in pulsed IR LED power), then the shaded side of stones, plants, or footprints within this 6-meter circle the ground would have an influence on the LED which is hundreds of times larger than a tiny gradient from a metal object buried below the surface.
Perhaps it is time to look for a different secondary effect of buried metal object phenomenon to explain why the IR LED power would change when pointed at the treasure location?
Best wishes,
J_P