HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (68) Citing Articles via Google Scholar Google Scholar Articles by Hook, W. R. Articles by Hook, P. B. Search for Related Content PubMed Articles by Hook, W. R. Articles by Hook, P. B. Agricola Articles by Hook, W. R. Articles by Hook, P. B.

Remote Diode Shorting Improves Measurement of Soil Water by Time Domain Reflectometry

Dep. of Biology, Univ. of Victoria, P.O. Box 1700, Victoria, BC V8W 2Y2; Canada

P. B. Hook

Dep. of Range Science, Colorado State Univ., Fort Collins, CO 80523

* Corresponding author.

ABSTRACT

We describe a new time domain reflectometry (TDR) technique that increases the reliability of soil water content measurements. Remotely switched shorting diodes in combination with differential detection techniques greatly increase the effective amplitude of problem reflections and significantly reduce background noise. Reliable detection of the two reflections that define the apparent dielectric constant of soil was achieved in all laboratory and field conditions. This, for example, enables measurement of volumetric water content in saline or layered soils and allows the use of long connecting cables. Additionally, increased signal-to-noise ratios should allow the development of significantly less complex and expensive measurement systems. A three-rod probe with a single diode was used to evaluate reflections from the air-soil surface; reflected signal levels were increased 10:1 for short cables and 56:1 for a probe located at the end of a 100-m cable. A three diode probe was employed to demonstrate performance in a simulated layered soil; the correct time of arrival of the reflection from the rod end was readily measured even though the reflection was attenuated by a factor of 2500:1. A strip-line two-segment probe was used to measure water content in two adjacent sand layers, providing a 23:1 signal-to-background noise ratio. For all these probes, waveform subtraction was used to remove virtually all background noise.

Received for publication September 30, 1991.

This article has been cited by other articles:

				T. J. Heimovaara, J. A. Huisman, J. A. Vrugt, and W. Bouten Obtaining the Spatial Distribution of Water Content along a TDR Probe Using the SCEM-UA Bayesian Inverse Modeling Scheme Vadose Zone J., November 1, 2004; 3(4): 1128 - 1145. [Abstract] [Full Text] [PDF]

				M. Persson, D. Bendz, and P. Flyhammar Time-Domain Reflectometry Probe for Water Content and Electrical Conductivity Measurements in Saline Porous Media Vadose Zone J., November 1, 2004; 3(4): 1146 - 1151. [Abstract] [Full Text] [PDF]

				C. F. Souza, D. Or, and E. E. Matsura A Variable-Volume TDR Probe for Measuring Water Content in Large Soil Volumes Soil Sci. Soc. Am. J., January 1, 2004; 68(1): 25 - 31. [Abstract] [Full Text] [PDF]

				W. R. Hook, T. P. A. Ferre, and N. J. Livingston The Effects of Salinity on the Accuracy and Uncertainty of Water Content Measurement Soil Sci. Soc. Am. J., January 1, 2004; 68(1): 47 - 56. [Abstract] [Full Text] [PDF]

				D. A. Robinson, D. A. Robinson, S. B. Jones, J. M. Wraith, D. Or, and S. P. Friedman A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry Vadose Zone J., November 1, 2003; 2(4): 444 - 475. [Abstract] [Full Text] [PDF]

				R. C. Harlow, R. C. Harlow, E. J. Burke, and T. P. A. Ferre Measuring Water Content in Saline Sands Using Impulse Time Domain Transmission Techniques Vadose Zone J., August 1, 2003; 2(3): 433 - 439. [Abstract] [Full Text] [PDF]

				G. C. Heathman, P. J. Starks, and M. A. Brown Time Domain Reflectometry Field Calibration in the Little Washita River Experimental Watershed Soil Sci. Soc. Am. J., January 1, 2003; 67(1): 52 - 61. [Abstract] [Full Text] [PDF]

				C. Nichol, R. Beckie, and L. Smith Evaluation of Uncoated and Coated Time Domain Reflectometry Probes for High Electrical Conductivity Systems Soil Sci. Soc. Am. J., September 1, 2002; 66(5): 1454 - 1465. [Abstract] [Full Text] [PDF]

				C. M. P. Vaz and J. W. Hopmans Simultaneous Measurement of Soil Penetration Resistance and Water Content with a Combined Penetrometer-TDR Moisture Probe Soil Sci. Soc. Am. J., January 1, 2001; 65(1): 4 - 12. [Abstract] [Full Text]

				S.D. Logsdon Effect of Cable Length on Time Domain Reflectometry Calibration for High Surface Area Soils Soil Sci. Soc. Am. J., January 1, 2000; 64(1): 54 - 61. [Abstract] [Full Text]