ACTIVATION ENERGIES AND TEMPERATURE EFFECTS FROM ELECTRICAL SPECTRA OF SOIL

Abstract

Apparent permittivity often has soil-specific temperature responses and soil water responses. These variations affect dielectric sensors, often requiring site-specific calibrations. Variations of permittivity as a function of frequency and temperature can be used to calculate activation energies. The purpose of this study was to examine permittivity-temperature responses for six soils and variation in calculated activation energies. Each of the six soils was packed into a truncated coaxial cell and the permittivity spectra were determined for a range of water contents and temperatures. Activations energies caused by charge transfer or rotation were then calculated. The rotational activation energy was not correlated with temperature, did not vary across frequencies, and was not significantly affected by soil differences. Charge transfer activation energy was significantly less for Cecil (kaolinite and quartz-dominant mineralogy) than for Weld or Okoboji (smectites-dominant mineralogy). There were significant positive temperature correlations for the direct current electrical conductivity and for the real permittivity at low frequencies, but not at higher frequencies. Delineation of these temperature and activation energy responses is necessary for describing how various soils respond to electromagnetic measurements.