The Time Domain Reflectometry (TDR) Measurement Principle

Measures the time taken (in nanoseconds) for an electromagnetic pulse to propagate along a waveguide surrounded by soil. Time of travel, or velocity, of this pulse is effected by the dielectric constant (Ka) of the soil. Wetter soil with a higher dielectric constant, produces a slower velocity pulse. TDR measures volumetric soil water (VSW%) independently of all other soil variables, including density, texture, temperature and electrical conductivity. TDR does not require in-situ calibration to accurately measure VSW%.

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