Abstract
To establish a method to monitor the vertical profile of volumetric water content (θ) near soil surface, a multi-wire profile probe (MWP probe) was designed and applied to the θ-profile observations during the evapora-tion processes in sand and decomposed granite soil. The probe consists of eight sets of the 3-wire TDR (time do-main reflectometry) probes, which are attached to a print-circuit board with a low permittivity, and is capable of measuring relative permittivity (εmwp) at intervals of 3 mm. The relationship between εmwp and θ for sand did not agree with one derived from Topp equation because the board had the influence on the εmwp measurements. Thus, we calibrated the probes for sand with different moisture con-ditions and found that the probes can determine θ within acceptable accuracy. In the evaporation processes, the ob-served θ-profiles showed that the moisture contents for sand at 3 and 6 mm depths locally decreased in the initial stage of the process, while the moisture contents for de-composed granite soil uniformly decreased at any depth. We concluded that the designed MWP probe would be useful for millimeter-interval measurements of vertical θ-profiles near soil surface.
