Jonathan Herring, Channabasappa Eswarappa and Wolfgang J.R. Hoefer
Gabel Corporation design and manufacture soil moisture probes which operate by measuring the time taken for pulses to travel along a fixed length of the probe. An increase in the level of moisture around the probe slows down the pulses. The TLM method has been used to directly model the operation of various probe configurations in the time domain for soils of different properties. By visualizing the fields, the effect of non-homogeneities (air gaps, water pockets, etc.) in the soil surrounding the probe can be seen. A typical result is shown in fig. 1, in which the electric field at a point in the soil is shown against time and distance along the probe, for the case of an open-circuit termination.