This Small Business Innovation Research (SBIR) Phase I project will develop new technology for the separation of ultra-fast-rise-time incident and reflected step functions needed for the development of an integrated differential Time Domain Reflectometer (TDR) to be used in soil water content measurement. Because of residual reflections from circuit board striplines terminated in variable soil loads and reflections from wetting fronts and discontinuities in the soil, the derivation of propagation time, permittivity and water content are subject to errors caused by the vector addition of the spurious, shorter-term reflections with the main reflection from the end of the waveguide. The characteristics of the interfering spurious signals vary with the soil environment. The overall waveform appearing at the TDR digitizer is a composite image of an incident step, a reflected wave and the set of spurious signals. The research required is that of characterizing the spurious signal patterns and of developing machine learning and signal processing algorithms to remove their impact from the derivation of reflected wave propagation time. Identification and timing of wetting fronts will also be included to provide sensor users with infiltration monitoring capability. The broader impact/commercial potential of this project is to provide an affordable and easily deployed means of accurately measuring soil water content, including the credible measurement of water uptake by food crops. This capability will facilitate significant increases in water use efficiency - the foundation for growing high quality food with less water. The value proposition to crop growers is reduced marginal costs and increased crop yield and quality, with a potential payback time of one to two growing seasons. Commercial adoption of soil moisture sensing technology will help manage the increased cost and demand for fresh water, of which over 70% of consumption goes to agriculture. The technology will also provide a stable and credible measurement tool for studying and monitoring watershed dynamics for flood and drought prediction, for monitoring dams, mudslide areas and levees for potential failure and for studying the impact of soil water dynamics on weather. Current tools for these measurements are either heavily regulated (neutron probe), difficult to install (Time Domain Transmissometer probe) or provide unstable readings with changing soil electrical conductivity and compaction (capacitive probes).
