FIG. 5. Comparison of the measured _r' (real component of relative complex permittivity) and _r'' (imaginary component of relative complex permittivity) temperature (T) response with apparent permittivity, _a, calculated using Eq. [3]. The Ames soil is representative of high _r'' soils, and the Tif5 soil is representative of low _r'' soils. Where _r'' is low, there is little impact on _a, and sensor type is not critical.