Detection of urban tree roots with the ground penetrating radar

Abstract

To evaluate the efficiency of the ground penetrating radar (GPR) in the detection of urban tree roots, this technique was tested on two trees in the urban environment and a controlled study involving roots that were pruned and buried at known depths and orientations. Using the 400 MHz antenna on clay laden soils, the GPR system, under controlled conditions was confirmed to have the capability to evaluate the presence of buried roots positioned at various orientations and at various depths in the ground but accurate detection was limited to roots that had a diameter greater than 0.05 m. The GPR was also tested for its ability to map entire tree root systems in the field. Two surveys involving different tree species (Khaya senegalensis and Swietenia macrophylla) were used to test the capability of the GPR system to detect roots in the soil at various depths. This study further confirmed that only coarse roots (with diameters greater than 0.05 m) were detected by the GPR system. Following the survey, S. macrophylla was excavated with an air spade to remove soil from the roots for the purpose of evaluation. The findings suggest that the presence of fine roots in the soil was generally not detected by the radar. The GPR was also not able to distinguish between roots that were crossing over each other from those that were simply branching away.