2008 Joint Annual Meeting (5-9 Oct. 2008): Analysis of Coaxial Soil Cell.
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661-6 Analysis of Coaxial Soil Cell.



Tuesday, 7 October 2008: 10:30 AM
George R. Brown Convention Center, 362F
Mathew Pelletier1, Robert Schwartz2, Steve Evett3, Bobbie McMichael4, Robert Lascano4, Dennis Gitz5, Jeffrey Baker6 and Paxton Payton7, (1)USDA-ARS, 1604 E FM 1294, Lubbock, TX 79403
(2)USDA-ARS, USDA-ARS Consv. & Prod. Res. Lab., PO Drawer 10 2300 Expt. Sta. Rd., Bushland, TX 79012
(3)Soil and Water Management, USDA-ARS, 2300 Experiment Station Road, PO Drawer 10, Bushland, TX 79012
(4)USDA-ARS, 3810 4th ST, Lubbock, TX 79415
(5)USDA-ARS, Cropping Systems Research Laboratory, 3810 4th Street, Lubbock, TX 79415
(6)USDA-ARS, USDA-ARS, 302 West I-20, Big Spring, TX 79720
(7)USDA ARS, PSGD, CSRL, 3810 4th St, Lubbock, TX 79415
As the research community moves towards research with higher accuracy demands than traditional TDR measurements can provide, the natural evolution of the science will be to transition toward Network Analyzer type measurements in the frequency domain due to the significant improvement in the accuracy and dynamic range the Network Analyzer technique provides over the traditional time domain TDR measurements.  In moving from a measurement of apparent permittivity in the time domain towards a measurement of true permittivity and loss in the frequency domain; of critical need is to remove the response of the cable, instrument and TDR or coaxial probe from the measurement.  In moving toward measurements of true permittivity, of critical need are calibration methods that couple models such as Clarkson and Kraft’s coaxial impedance models, to high quality calibration methods such as are utilized in the microwave engineering field for use in Network Analyzer measurements.  In moving forward, this research reexamines the terminated coaxial cell from a theoretical basis to re-examine underlying assumptions of the Clarkson and Campbell-Kraft models and then applies the developed theory towards confirmation via experimentation.  The results of the findings highlight key areas where the Clarkson and Campbell-Kraft models are not valid along with ways to mitigate the errors that arise due to the standard TDR practice’s deviation from the ideal situation modeled by Clarkson and Campbell-Kraft models.  This paper concludes by utilizing the theory to provide a model for use in through transmission measurements and a new FDT design to perform high accuracy measurements of true complex permittivity.
See more of: Soil Moisture: Advances in Design and Development of Water Content, Matric Potential, and Flux Measurement Methods for the Critical Zone: I
See more of: S01 Soil Physics