Imaging of Water Content Distributions inside a Lysimeter using GPR Tomography

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Abstract
In a study to investigate water content distributions inside a lysimeter in a noninvasive manner, we used ground penetrating radar (GPR) tomography. Our main objective was to evaluate the temporal changes and spatial distributions of the volumetric water content after a short but intensive irrigation of part of the lysimeter. High frequency GPR antennas of 1‐GHz nominal frequency were used because of the small spatial dimensions of the investigated lysimeter (cylinder of 1.5‐m height and 1.2‐m diameter) and the desired spatial resolution in the range of decimeters. To ensure a relatively steady distribution of water inside the lysimeter for the time‐consuming tomographic survey, simple parallel transmission measurements were used to track the water dynamics. Water contents and water content changes were calculated by means of a mixing formula describing the relation between electromagnetic wave propagation velocity and the water content. The transmission measurements indicate a diffusive process following the irrigation for a duration of several hours. The tomographic measurements clearly show the area of increased water content associated with the irrigation.