Time Domain Reflectometry (TDR) is becoming a popular method of measuring water content. By measuring the time it takes for a step-waveform to propagate down and back an open circuited transmission line, one can determine the dielectric constant of the media. Regression equations can then be used to determine water content from the dielectric constant. Problems occur, however, in regions of high salinity (or electrical conductivity) in that the phase velocity and attenuation of electromagnetic waves as well as the characteristic impedance of the transmission lines are functions of frequency as opposed to constants. This results in dispersion of the low frequency components and attenuation of the high frequency components of a TDR step-waveforrn which causes errors in the determination of water content. This Phase I research project will investigate using existing electromagnetic and soil physics models to develop an algorithm to enable TDR systems to accurately measure water content and salinity over a wide range of water contents, salinities and soil types with a minimum amount of calibration.Applications:The results will potentially lead to a model for electromagnetic wave propagation in soils that is general purpose enough to be able to determine water content and salinity over wide ranges of those parameters in different soils with a minimum of calibration. This model would be incorporated into a new software product to be used with existing TDR hardware for water content and salinity measurements. Potential benefits are water quality assessments near hazardous waste dumps, irrigated agriculture management and concrete/wood products analysis.
