Determining the size of internal air cavities in linden (Tilia Europaea) trunks via ground penetrating radar

Journal of Applied Geophysics. 2025. Vol. 240. Article 105761.

M. S. Sudakova, Terentieva E. B., Soldatenko A. M., Kalashnikov A. Y., Palenov A. Y.

Detecting and measuring tree decay is essential part of urban forest management and tree risk assessment in public safety. Invasive and moderately invasive decay-detecting devices, such as constant feed drills, are accurate for locating wood decay in a tree. In contrast, tomography devices are either less damaging to tree tissues (the case of acoustic tomography) or even non-invasive (GPR tomography) but may represent difficulties in processing and interpretation. This paper considers detecting and characterizing the geometry of decay and cavities in live trees using Ground Penetrating Radar (GPR). Combined multi-offset ray-based GPR tomography and zero-offset GPR techniques were validated on five trees selected in the urban environment in the Central Park of Culture and Recreation named after Maxim Gorky (Gorky Park, Moscow). The zero-offset measurements were carried out at three different heights, 60 cm, 140 cm, and 180 cm, while GPR tomography of trunks was done at 140 cm. Consequently, these trees were felled and sectioned, and decay/void measurements were conducted for tree sections at 140 cm height. We demonstrated that the combination of multi-offset GPR tomography with zero-offset GPR allows accurately differentiating between rot /void and healthy wood layers and identifying the position of cavities and decay in tree trunks. There were no false positive or false negative results in void detection, while the error in determining the area was no more than 10 % of the trunk’s area. We recommend combining these approaches to produce accurate contours of internal wood defects and consider the result obtained as a basis to build a three-dimensional model of a trunk in situations where conventional invasive forestry approaches are not applicable.

Keywords: non-destructive testing, Heritage forest park, Gpr tomography, Tree decay, City trees