ARS | Publication request: MEASUREMENT AND MODELING OF TDR SIGNAL PROPAGATION THROUGH LAYERED DIELECTRIC MEDIA

Submitted to: Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: October 20, 2003
Publication Date: November 1, 2003
Citation: Schaap, M.G., Robinson, D.A. 2003. Measurement and modeling of TDR signal propagation through layered dielectric media. Agronomy Society of America, Crop Science Society of America, Soil Science Society of America Annual Meeting. CD-ROM. Denver, CO, Nov. 2-6, 2003.

Technical Abstract: Layered dielectric materials are often encountered in the natural environment due to differences in water content caused either by a wetting or drying front. This is especially true for coarse-grained materials such as sandy soils, sediments and some rocks that have very distinctive layers of water content. This paper examines the issue of how the permittivity along a TDR probe is averaged as a function of layer thickness and probe orientation. Measurements of apparent permittivity using TDR are presented for two, three and multi layer materials. TDR waveforms are modeled for multiple layers of varying thickness and show a change in the averaging of the apparent permittivity from refractive index to arithmetic when more thin layers are present. Analysis of the modeled results shows that the averaging regime is frequency-dependent. However, broadband techniques applied to materials with a few layers will generally produce refractive averaging. A transition to arithmetic averaging is found for systems having many (>4 layers). Narrow-band methods may be very sensitive to layering and may perform