Impedance analysis of TDR signals: Application to water content measurements in saline soils. (5591)
Authors:
P. Castiglione* - Montana State University J.M. Wraith - Montana State University D. Or - University of Connecticut
Abstract:
Fundamental soil properties such as texture, wetness, and adsorbed and dissolved chemicals can be inferred from the dielectric permittivity at radar frequencies.
Notably, the water content can be determined even for highly saline soils, for which traditional travel time analysis of TDR signals is known to fail. We present a
procedure based on impedance analysis of transmission lines for TDR measurement of soil permittivity up to about 4 GHz. An advantage over the commonly applied scatter function approach is that no assumption of a particular dispersion model is required, nor is determination of the input voltage pulse. Moreover, any spurious reflections due to cable, connectors or other impedance mismatches along the line can be easily taken into account through calibration with two standards of known permittivity. The technique was tested using 165 and 5 mm long coaxial cells and a Tektronix cable tester. Results for common solvents and aqueous electrolyte
solutions are in good agreement with literature values. Dielectric spectra for soils of different texture and pore water EC up to 30 dS/m were analyzed to identify a
suitable frequency range where permittivity values correspond to the “effective”
dielectric constant obtained from travel time analysis. Soil water contents were then estimated using the Topp equation, giving values within 5% of gravimetric
measurements.
Speaker Information: Paolo Castiglione, Montana State University, 818 Leon Johnson Hall, MSU, Bozeman, MT 59715; Phone: 406-994-7737; E-mail: [email protected]
Session Information: Wednesday, November 3, 2004, 7:50 AM-12:05 PM Presentation Start: 8:55 AM
Keywords: TDR; dielectric permittinity; saline soil; frequency domain