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Soil Physics Note

Experimental Limitations of Time Domain Reflectometry Hardware for Dispersive Soils

National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011

^* Corresponding author (logsdon{at}nstl.gov)

Time domain reflectometry (TDR) has been used to determine soil water content. Multiple attachments and long cables may result in unreliable data for dispersive soils, but these attachments are necessary for automated field monitoring at multiple sites and depths. The objective of this study was to experimentally determine the effect of attachments on the TDR waveform for a parallel probe with a balun. The probe with parallel waveguides and balun was successively attached to the front panel of the cable tester (Level 1), to a transient suppressor (Level 2), to the first level multiplexer (Level 3), or to a second level multiplexer (Level 4). Each attachment level significantly reduced frequency bandwidth, and Level 4 frequency bandwidth was about half that of Level 1. The greatest attenuation decrease was between Levels 1 and 2. Attenuations due to TDR hardware make it difficult to obtain useful waveforms for determining soil water content.