Advanced Analysis of Electromagnetic Waves for Intrinsic Soil Properties

Purdue University, West Lafayette IN

Investigators

Abstract

This project will apply time domain and frequency domain analyses of Time Domain Reflectometry (TDR) signals to estimate intrinsic soil properties such as water content, density, conductivity, specific surface area, and macroscopic soil. Time Domain Reflectometry is a technology widely accepted as fast, safe, and economical for geotechnical, geo-environmental, and agricultural engineering applications. In conventional TDR analysis, volumetric water content is determined from the travel time of the electromagnetic waves in a soil probe, and conductivity is obtained from the amplitude of the signal at long times. However, much more information about the intrinsic properties of the soil is contained in the measured TDR waveforms, which is generally not utilized. The additional information can be obtained by using inversion theory in the frequency-domain. To achieve this goal, accurate models are needed to describe the electromagnetic wave propagation in the TDR system and to relate soil intrinsic properties to the soil electromagnetic properties. The methodology makes use of full waveform analysis of the TDR system combined with a volumetric dielectric mixing model for the soil properties. This research involves refining and validating both forward modeling and inverse theory. The four major tasks of this research include: 1) Advance the dielectric mixing models and forward models for electromagnetic wave propagation in soil; 2) Extend the inversion theory using the refined dielectric models and perform resolution and covariance analysis; 3) Validate the forward and inverse solutions; and 4) Develop a robust methodology for practical use. The overall goal is for the TDR technique to become a more powerful and yet practical tool for identifying soils and determining soil intrinsic properties. Results of this research also will make TDR a more valuable tool for studying fundamental soil behavior including compositional characteristics, volumetric fraction of soil phases, soil-water interaction, and soil microstructure. The research will enhance the value of electromagnetic measurements not only in geotechnical and geo-environmental engineering, but also in agronomy, soil science, and agricultural engineering. Broader impacts of this research will be achieved by the involvement of undergraduate and graduate students, continuation and expansion of participation of testing partners from academia, industry, and government, development of ASTM Standards for the newly developed technologies, publication in the open literature, presentations at technical society meetings, and short courses to introduce these new technologies.