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The Author and Vermont Caver Peter Grant using the
D-Q receiver to attempt a ratiometric depth measurement of the Dream Lake
siphon in Culverson Creek Cave, West VA, which is nearly 700 feet below
the surface. The 25 foot aluminum pole is in ten 30-inch sections which
were added at the bottom to raise the loop. It is resting against the tree
to steady it and get it horizontal. At this depth, moving a few feet from
ground zero does not change the signal strength. The pole was tested prior
to the trip to make certain that it had no noticable effect on the magnetic
field.
The Ratiometric technique involves recording the Beacon's signal strength with the Receive loop horizontally on the ground, then repeating with the loop raised a known height over Ground Zero. A simple cubic equation gives the "free space" depth of the Beacon. The ground level signal strength can be used by itself to calculate the "free space" depth by "absolute signal strength" if the Beacon and receiver are calibrated on the surface at a known spacing either before or after the trip. |