Graduate Thesis Or Dissertation
 

Water content and electrical conductivity profile measurements for dispersive media using enhanced time domain and frequency domain models

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3484zm123

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  • Water conservation and water quality are rapidly increasing in importance in all areas of the world. The ability to accurately measure soil water content and salinity, over a wide variety of conditions, is key to meeting this need. A set of forward prediction models and waveform interpretation algorithms to extract Volumetric Water Content (WC) and Electrical Conductivity (EC) profiles vs. position and time for electrically lossy and dispersive geophysical and biological media are presented. These are applicable to both Time Domain and Frequency Domain Electromagnetic Wave Propagation Transmission and Reflection measurements. These forward prediction models are developed using physically based First Principles models from the Theory of Electromagnetics together with Scattering (S) Parameter and Transmission (T) Parameter network modeling techniques applied to wave propagation in various media with cascaded domains of different properties. The interpretation algorithms fit the pre-derived Forward Prediction models to the measurement data via lookup tables, interpolation and optimization methods. Presented applications include the transmission line methods of Time Domain Reflectometry, Time Domain Transmission, Frequency Domain Reflectometry and Frequency Domain Transmission including high dynamic range Frequency Domain Vector Network Analysis. Other applications include Ground Penetrating Radar and Microwave Remote Sensing. The models account for temporal and spatial heterogeneity to obtain WC and EC vs. time and position. Models are introduced for composite media with multiple constituents of varying Ohmic (EC) and dielectric (electric permittivity) properties accounting for dispersive frequency dependence and loss. These models interpolate between the physical upper and lower bounds of parallel and serial influences of each of the capacitive and conductive constituents. New models are also introduced accounting for charged interfaces and resulting bound and semi-bound water constituents within the pore spaces of soils containing clay or organic matter fractions resulting in a transition zone from bound to free water (via a semi-bound water zone) impacting the frequency dependence on electric permittivity. Validations of the models are presented via comparisons to actual measured data over wide ranges of water content, electrical conductivity and soil types.
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