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Report, 1998

Sources of errors in time domain refloctometry measurements of soil moisture

Carlsson, Magnus


In the monitoring of soil water Time-Domain Reflectometry (TDR) has gained widespread use. TDR has proved to be useful both in determination of soil water content and soil bulk electrical conductivity. These measurements are, however, complex and there are many sources of errors to consider. The purpose of this investigation is therefore to identify errors, the causes of these errors and to suggest improvements. This was achieved by a literature study as well as by two experiments, one conducted in the field and one conducted in the laboratory. Four TDR-systems were tested. The results show that errors can be classified in two groups, errors which is influencing the determination of the dielectric constant, Ka, and errors affecting the conversion of Ka to volumetric water content, ??. The former type can be further divided into errors which concern the quality of the trace and errors influencing the evaluation of the trace. Unbalanced probes and long cables were identified as contributing to uncertainties. Errors from conversion of Ka to ?? were considered when the systems were calibrated. One of the programs tested allows convenient one point calibration with a trace offset parameter. The advantage of re-evaluation of measurements with individual settings also permits increased accuracy of measurements


TDR; soil water; soil moisture

Published in

Avdelningsmeddelande / Sveriges lantbruksuniversitet, Institutionen för markvetenskap, Avdelningen för lantbrukets hydroteknik
1998, number: 98:5
Publisher: Institutionen för markvetenskap, avdelningen för lantbrukets hydroteknik

Authors' information

Carlsson, Magnus
Swedish University of Agricultural Sciences, Department of Soil and Environment

UKÄ Subject classification

Fish and Aquacultural Science
Agricultural Science

URI (permanent link to this page)