A Reflectivity-Based GPR Signal Processing Methodology for Mapping Tree Root Systems of Street Trees

Street trees are broadly acknowledged to be an essential asset of cities. Nonetheless, the growth of tree roots can lead to critical damage, such as the uplifting or cracking of road pavements and curbs, with severe implications on the infrastructure's safety. For this reason, the assessment and control of tree root systems' development have become crucial task in forestry and urban management. Within this framework, Ground Penetrating Radar (GPR) is widely recognised as an effective non-destructive testing (NDT) method for the monitoring and assessment of road infrastructures. This study aims to demonstrate the capability of GPR in mapping the root system's architecture of street trees. To this end, a GPR system equipped with a 700 MHz central frequency antenna was employed to investigate the area around a street tree, located in the vicinity of a flexible pavement structure. A novel processing framework based on the analysis of the signal reflectivity was implemented, in order to automatically identify the reflections from the pavement layers and apply dedicated advanced signal processing techniques. A multistage data processing methodology was employed to map the tree root system architecture. Finally, information on the mass density of roots at different depths was also provided. Results have proven the potential of the proposed methodology to achieve an automatic detection and mapping of roots under road pavements.