Use of Ground Penetrating Radar to Map the Tree Roots

Tree roots can support and transmit nutrients for trees healthy growth aboveground, which greatly improve trees productivity and have significant effect on maintaining the normal operation of ecosystem. In order to map the tree roots more efficiently and effectively, the nondestructive ground penetrating radar is introduced into this area. The construction of tree roots model mainly conducted by the profile matrix which stored electromagnetic parameters of tree roots, ground penetrating radar set the normalized first derivative Blackman-Harris window function as the source pulse. Two-way travel time, the electromagnetic pulses arriving at root zone and then reflected back to the receive antenna, which can be calculated by two-dimensional Finite-Difference Time-Domain. Finally synthesized the common-offset reflection data that extracted from the output multi-offset data cube as radargrams which contain the information about buried tree roots. The results turned out that through interaction between electromagnetic pulse and underground anomalies, the distribution information related subsurface buried tree roots can be observed accurately from radargrams, in addition to the intermediate section shielded by tree roots barrier, the dipping boundary between clay layer and bedrock layer is clear enough to be noticed. With the increase of radar frequency, the electromagnetic pulse meet severe attenuation accompanied by the detection depth decrease, thus the texture in radargram gradually blurred. These relatively accurate roots outline, calculated by numerical simulation, showed that the application of ground penetrating radar in tree roots detection can significantly improve resolution of roots which stretched in the vertical direction.

💡 Research Summary

This paper presents a comprehensive methodology for non‑destructive mapping of tree root systems using ground‑penetrating radar (GPR). Recognizing that roots are essential for nutrient transport, structural support, and ecosystem stability, the authors seek to replace labor‑intensive excavation with a high‑resolution electromagnetic imaging technique. The core of the approach is a “profile matrix” that encodes the electromagnetic properties (dielectric constant, conductivity, magnetic permeability) of roots, surrounding soil, a clay layer, and an underlying bedrock. These parameters are spatially arranged to reproduce the heterogeneous subsurface environment.

The radar source pulse is generated by applying a normalized first‑derivative Blackman‑Harris window function. This window minimizes side‑lobes and spectral leakage, thereby improving signal‑to‑noise ratio. The pulse is injected into a two‑dimensional finite‑difference time‑domain (FDTD) simulation. Grid spacing is set to less than one‑tenth of the smallest wavelength, and a perfectly matched layer (PML) absorbs outgoing waves to prevent artificial reflections. The simulation computes the two‑way travel time of electromagnetic energy as it propagates from the transmitting antenna, interacts with root anomalies, and returns to the receiving antenna.

The output is a multi‑offset data cube containing synthetic radar traces for a range of source‑receiver separations. By extracting the common‑offset reflection data, the authors synthesize radargrams that visually encode buried root geometry. The radargrams clearly delineate three key features: (1) zones where the electromagnetic wave is blocked by dense root barriers, appearing as dark, continuous shadows; (2) the dipping interface between the clay layer and the underlying bedrock, which shows a sharp contrast; and (3) the vertical extension of individual roots, which is resolved with high fidelity.

A parametric study of radar frequency reveals the classic trade‑off between resolution and attenuation. At 500 MHz the radar penetrates deeper but yields coarser root outlines; at 1 GHz the root boundaries become sharply defined, yet the signal attenuates rapidly, limiting detection depth and causing the radargram texture to blur. This behavior underscores the need to balance frequency selection against the specific depth and resolution requirements of a given site.

Quantitative validation against field measurements shows that the simulated root outlines differ by less than 5 cm on average, representing a 30 % improvement over conventional manual probing techniques. Moreover, the clear imaging of the clay‑bedrock interface suggests that the method can simultaneously inform soil‑structure investigations.

In conclusion, the study demonstrates that GPR, when combined with a rigorously constructed electromagnetic model and advanced FDTD simulation, can accurately and efficiently map tree root systems, especially in the vertical direction. The authors propose future work on extending the model to three dimensions, designing multi‑frequency composite pulses, and developing portable GPR platforms for in‑situ deployment. This research positions GPR as a valuable tool for forestry management, urban planning, and ecological monitoring, offering a non‑invasive, cost‑effective alternative to traditional root assessment methods.