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> The required depth depends on the soil diffusivity and the temperature > stability required. > It is instructive to install thermometers at depth intervals of a foot > or so and record the temperature fluctuations experienced by each > thermometer. > This was first done around 1860 by Forbes. > I repeated the experiment in 1966. There was an interesting bit in the last Agilent Measurement Journal about a product that uses an ordinary communications-grade fiber as a thermometer. >From what I remember, they send a laser pulse down the fiber, then look at the backscatter, correlating time-of-flight with the Raman-scattering lines (Stokes and anti-Stokes). One of those spectral lines is temperature-dependent while the other isn't, so by recording the separation, they end up with is a graph of temperature versus distance along the fiber, gathering up to a few kilometers' worth of data with what looked like sub-meter resolution. No doubt this effect is old hat to physicists on the list, but I'd never heard how it worked before. So if you buried a fiber like this, you'd presumably get a great picture of what happens with temperature at various depths. Plotting the temperature-versus-distance on a waterfall display gives a nice diurnal picture. The article used it to study water temperature along the course of a stream, but you could think of plenty of other uses for 2D remote temperature sensing. -- john, KE5FX _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
