Recent interest in soils and hydrologic modeling has increased the need for information concerning the depth and movement of ground water. Ground-penetrating radar (GPR) was used eight times over a two-year period to chart water table depths and ground-water flow patterns within a 32-ha forested site in northwestern Indiana, USA. Radar imagery was correlated with depths to the water table in 16 observation wells. The velocity of propagation ranged from 0.0508 m/ns to 0.1606 m/ns at these wells. Propagation velocities were generally slower during the spring and early summer months when depths to the water table were relatively shallow. Propagation velocities were faster through dunes than through the more poorly drained interdunes. Because of the spatiotemporal variability in propagation velocities and the known complexity of soil and landform patterns, a predictive equation based on water table depths and two-way travel times was developed for each GPR survey. In this setting, the use of a predictive equation based on multiple GPR measurements over a known reflector substantially improved the accuracy of radar depth interpretations over single or averaged measurements.
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