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THE TACQ COMPUTER PROGRAM FOR AUTOMATIC TIME DOMAIN REFLECTOMETRY MEASUREMENTS: II. WAVEFORM INTERPRETATION METHODS

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASAE.  VOL. 43(6): 1947-1956 . (doi: 10.13031/2013.3100) @2000
Authors:   S. R. Evett
Keywords:   TDR, Time domain reflectometry, Computer program, Soil water content, Waveform interpretation, electrical conductivity, BEC

Despite the increased use of time domain reflectometry (TDR) for measurement of soil water content and bulk electrical conductivity (BEC), there are few public releases of software for TDR system control. Even though graphical interpretation of the waveform to find pulse travel times is key to success with the method, the few published descriptions of computer methods are incomplete. The TACQ program, under development since the early 1990s on a wide variety of soils, allows control of multiplexed systems supporting up to 256 TDR probes. Waveform interpretation methods are user-controlled and allow interpretation using various methods reported in the literature or methods available only in TACQ. The default methods allow automatic interpretation of waveforms from a variety of media including loose, air-dry soil, and wet clay. The present study shows that interpretation methods can have a large effect on reported water contents. The additive effects can result in water content change errors as large as 0.08 m 3 m 3 as the soil wets and dries, and as TDR system temperature changes over a season. Thus, the interpretation methods used should be reported in rigorous studies involving TDR water content determination, calibration, and temperature effects. The TACQ program, and documentation, may be downloaded from http://www.cprl.ars.usda.gov/programs/.

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