Dielectric properties of wet sediments versus temperature at 10-6,000 MHz
Abstract
Knowledge of the dielectric properties of sediments is important to studies of subsurface radiowave propagation, especially as it applies to ground-penetrating radar (GPR) operating in the 50-1,000 MHz bandwidth. In areas contaminated by nuclear waste and in desert environments, water within the soils can be unusually warm, with temperatures ranging up to 50° C. For the GPR bandwidth, past results suggest that relaxation effects may cause significant dispersion and loss of the radar signal within the subsurface. To this end, we have employed a network analyzer-based system with a modified HP805 coaxial-type sample holder to investigate sand and silt at water contents ranging from 0% to 30% and temperatures ranging from 0° C to 50° C. The correct operation of this system has been verified with methanol, ethanol, and isopropyl alcohol which are dispersive in the GPR frequency range. Preliminary results suggest that dry sand and silt, which have relatively constant dielectric response across our frequency range of interest, experience no enhanced dispersion at elevated temperatures. With increasing water content, however, we find increasing dispersion at higher temperatures: for nearly saturated sand and silt, the real part of the complex dielectric permittivity decreases by up to 25% at frequencies above 100 MHz while it decreases less, or even slightly increases, below this frequency. Other than the low frequency peak in e'' due to conductivity effects, there are no additional imaginary dielectric loss peaks at elevated temperatures or water contents for sand and silt-sized materials. Further investigations are planned for clay soils to control for grain size in quantifying temperature-dependent dielectric dispersion effects.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSMNS44A..03F
- Keywords:
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- 0609 Antennas;
- 0619 Electromagnetic theory