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United States Department of Agriculture

Agricultural Research Service

Title: Conventional Time Domain Reflectometry Systems

Author
item Evett, Steven

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: February 6, 2007
Publication Date: February 1, 2008
Citation: Evett, S.R. 2008. Conventional time domain reflectometry systems. In: Evett, S.R., Heng, L.K., Moutonnet, P., Nguyen, M.L., editors. Field Estimation of Soil Water Content: A Practical Guide to Methods, Instrumentation, and Sensor Technology. IAEA-TCS-30. International Atomic Energy Agency, Vienna, Austria. ISSN 1018-5518. p. 55-72.

Interpretive Summary: As a chapter in a book to be published by the International Atomic Energy Agency/FAO Joint Division, this publication will reach a wide audience of agriculturalists world wide, including scientists and practitioners. It contains detailed information on how to accurately sense soil water content and bulk electrical conductivity with the conventional time domain reflectometry (TDR) method, using components from the two major manufacturers, some of which were designed by the author. It provides insight into problems commonly encountered in using the TDR method, a method that is sensitive to the electrical properties of soils, including soil electrical conductivity, which itself increases with salinity and water content. Guidance on dealing with salinity problems and other measurement interferences is given. Instruction on data recording and analysis and useful software programs is also given. The theory and practice of TDR for soil water sensing is presented, with useful inferences drawn for solving measurement problems. A procedural guide is given for calibrating, installing and using the equipment; as is guidance for system integration to make best use of the available equipment at lowest cost. Particular attention is given to solutions for common problems of cabling, installation timing, custom probe construction, and integration of low-power, remote systems.

Technical Abstract: This chapter in a book to be published by the International Atomic Energy Agency/FAO Joint Division provides detailed information on how to accurately sense soil water content and bulk electrical conductivity with the conventional time domain reflectometry (TDR) method. Attention is given to integration of components from the two major manufacturers, some of which were designed by the author. Problems commonly encountered in using the TDR method are discussed. This method is sensitive to the electrical properties of soils, including soil electrical conductivity, which itself increases with salinity and water content. Guidance on dealing with salinity problems and other measurement interferences is given. The theory and practice of TDR for soil water sensing is presented, with useful inferences drawn for solving measurement problems. Software programs useful for data recording and analysis are discussed. A procedural guide is given for calibrating, installing and using the equipment; as is guidance for system integration to make best use of the available equipment at lowest cost. Particular attention is given to solutions for common problems of signal attenuation, cabling, installation timing, custom probe construction, data storage needs, and integration of low-power, remote data acquisition systems.

Last Modified: 7/23/2014
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