Non-invasive probing of the near-surface soil moisture profile

Time domain reflectometry imaging (TDRI) is a technique for non-invasive measurement of moisture content distribution. A solution to the 2-D problem has previously been described, and here we explain a configuration that provides a practical system for measuring a 1-D vertical profile of soil moisture. The measurement system consists of an enhanced TDR transmission line and reflectometer together with specialist software, to translate measurements of propagation times into a moisture content profile. We demonstrate a soil moisture accuracy of better than 2% for each 20 mm layer to 60 mm depth, with increasing accuracy loss for greater depths. However the attainable accuracy is dependent on the soil type and the dielectric model used for translation of permittivity profile to soil moisture profile. A practical depth limit for the current configuration is 100 mm. Assumptions and limitations of the technique will also be described.New Zealand Foundation for Research Science and Technolog