The Early Development of TDR for Soil Measurements

The early development of time‐domain reflectometry (TDR) for measuring water content in soils began somewhat by chance and continued almost in spite of the lack of support for the work from the sponsoring organizations. Following their first meeting, mutually supportive relationships quickly developed among the authors to sustain the research and development (R&D) program through the early difficult stages. The consistency across varied soils in the early findings buoyed up the authors' enthusiasm, but there was considerable reluctance by others to accept that one relative permittivity vs. water content relationship would apply as widely as claimed. The development of the first TDR instrument specifically for soil measurement highlighted a number of difficulties that may occur during the translation of scientific concepts and results to the instrumentation stage. An important method of dissemination of TDR results was the personal demonstration of the technique at conferences and workshops. These direct personal contacts often assisted others to pursue diverse applications, such as multiplexing for better spatial coverage, estimating liquid water in frozen soil, electrical conductivity, and solute movement. By 1987, TDR in soil had come of age with the presentation of five TDR papers from four nations at the Utah State Centennial Symposium. These experiences are offered as inspiration for others working on development research or perhaps as a warning of possible difficulties. In spite of which, this proved to be one of the most exciting and rewarding projects for the authors.