A small portable meter for soil heat conductivity and its use in the O'Neill test

A hypodermic needle is fitted, in its bore, with an electrical heating wire and a thermocouple. With certain precautions, its temperature increase yields data of soil heat conductivity. Very large local variations of the heat conductivity λ were found in the upper centimeters of the surface by this instrument at the USAF Great Plains Turbulence Project at O'Neill, Nebraska, in 1953.