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Fig. 1. Top and side view cross sections of a soil column showing the placement of access tubes, TDR probes, and thermocouples. Column sides were covered with aluminum foil. For axial sensitivity tests, each sensor was centered above its access tube and at a height (usually 30 cm above the soil surface) such that the soil (either dry or saturated) did not influence the sensor reading. Then the sensor was lowered in 2-cm increments, with a reading taken at each increment, until it passed through the access tube and reached a position below the soil surface that was lower than the depth at which further lowering did not influence the sensor reading (usually 30 cm below the soil surface).
