Diagnosing emerging infectious diseases of trees using ground penetrating radar

Ash dieback, acute oak decline (AOD) and Xylella Fastidiosa are Emerging Infectious Diseases (EIDs) that have spread rapidly in European forests during the last decade. Quarantine measurements have mostly failed to repress the outbreaks and millions of trees have already been infected. Identifying infected trees in a non-destructive manner is of high importance for monitoring, managing and preventing EIDs. The aim of this paper is to examine the capabilities of Ground Penetrating Radar (GPR) on evaluating the internal structure of tree-trunks and detecting tree-decay associated with EIDs. Traditionally used processing schemes tuned for GPR line-acquisitions are modified accordingly to be compatible with the new measurement configurations. In particular, a detection framework is presented based on a modified Kirchhoff and a reverse-time migration. Both of the aforementioned methodologies are compatible with measurements taken along closed irregular curves assuming a homogeneous permittivity distribution. To that extent, prior to migration, a novel focal criterion is used that estimates the bulk permittivity of the host medium from the measured B-Scans. The suggested detection scheme is successfully tested on both numerical and laboratory measurements, indicating that GPR has the potential to become a coherent and practical tool for detecting tree-decay associated with EIDs

The Use of GPR and Microwave Tomography for the Assessment of the Internal Structure of Hollow Trees

Peer reviewedPostprin

Assessing the internal structure of hollow trees using GPR and microwave tomography

Trees and woodlands are nowadays threatened by variety of aggressive diseases and fungal infections. As a result, internal decays in trees, can lead to the creation of cavities and large holes inside the trunks, which in turn can seriously undermine the stability and the integrity of the tree. In this regard, ground-penetrating radar (GPR) has recently proven to be an effective non-destructive testing (NDT) method, with the potential of providing information about the internal structure of trees. However, the particular shape of tree trunks prevents the use of traditional data processing techniques, and only limited information can be collected for tree health assessment purposes. This study shows the potential of GPR enhanced by a microwave tomography inversion approach in detecting tree cavities and hollows. A hollow tree was investigated by performing a set of circular GPR scans, and the internal structure of the trunk was reconstructed via tomographic imaging. The achieved results were validated by way of comparison with real sections cut from the tree and prove the validity of the proposed methodology in identifying the dimension and shape of cavities and hollows in tree trunks

Tree trunk inspections using a polarimetric GPR system

In this work, a novel signal processing framework for polarimetric GPR measurements is presented for inspection of tree trunks decay. The framework combines a polarimetric noise filter and an arc-shaped diffraction imaging algorithm. The polarimetric noise filter can increase the signal-to-noise ratio (SNR) of B-scans caused by the bark and the high-loss propriety of the tree trunk based on a 3D Pauli feature vector of the Bragg scattering theory. The arc-shaped diffraction stacking and an imaging aperture are then designed to suppress the effects of the irregular shape of the tree trunk on the signal. The proposed detection scheme is successfully validated with real tree trunk measurements. The viability of the proposed processing framework is demonstrated by the high consistency between the results and the real-truth trunk cross-sections

The Use of Ground Penetrating Radar and Microwave Tomography for the Detection of Decay and Cavities in Tree Trunks

Acknowledgements This paper is dedicated to the memory of Jonathan West; a friend, a colleague, a forester, a conservationist and an environmentalist, who died following an accident in the woodland that he loved.Peer reviewedPublisher PD

Novel approaches in GPR data processing for health monitoring of trees

The aggressive fungal attack is seriously threatening tree species in forests and woodlands in the UK and beyond. A lot has been said about the spread of disease and fungal attack on ash and oak trees in the United Kingdom and European countries. Within this context, Ground Penetrating Radar (GPR) has emerged as one of the most promising non-destructive testing (NDT) methods for acquisition of information about the internal structure of trees in terms of defect and their root system architecture. Nevertheless, current research has shown that there exists limited information and in depth studies within this important area of endeavour. This review paper reports on the current advances made within the context of GPR applications in health monitoring and assessment of trees and tree roots. This paper also discusses and reports on new areas of development including, the reverse-time migration, the microwave tomography and the pattern-recognition approaches within the signal processing and image analysis (interpretation) contexts

Health monitoring of trees and investigation of tree root systems using ground penetrating radar (GPR)

Evidence suggests that trees and forests around the world are constantly being threatened by disease and environmental pressures. Over the last decade, new pathogens spread rapidly in European forests, and quarantine measures have mostly been unable to contain outbreaks. As a result, millions of trees were infected, and many of these have already died. It is therefore vital to identify infected trees in order to track, control and prevent disease spread. In addressing these challenges, the available methods often include cutting of branches and trees or incremental coring of trees. However, not only do the tree itself and its surrounding environment suffer from these methods, but they also are costly, laborious and time-consuming. In recent years the application of non-invasive testing techniques has been accepted and valued in this particular area. Given its flexibility, rapidity of data collection and cost-efficiency, Ground Penetrating Radar (GPR) has been increasingly used in this specific area of research. Consequently, this PhD Thesis aims at addressing a major challenge within the context of early identification of tree decay and tree disease control using GPR. In more detail, two main topics are addressed, namely the characterisation of the internal structure of tree trunks, and the assessment of tree root systems’ architecture. As a result, a comprehensive methodology for the assessment of both tree trunks and roots using GPR is presented, which includes the implementation of novel algorithms and GPR signal processing approaches for the characterisation of tree trunks’ internal structure and the three-dimensional mapping of tree root systems. Results of this research project were promising and will contribute towards the establishment of novel tree evaluation approaches

Accurate Tree Roots Positioning and Sizing over Undulated Ground Surfaces by Common Offset GPR Measurements

Tree roots detection is a popular application of the Ground-penetrating radar (GPR). Normally, the ground surface above the tree roots is assumed to be flat, and standard processing methods based on hyperbolic fitting are applied to the hyperbolae reflection patterns of tree roots for detection purposes. When the surface of the land is undulating (not flat), these typical hyperbolic fitting methods becomes inaccurate. This is because, the reflection patterns change with the uneven ground surfaces. When the soil surface is not flat, it is inaccurate to use the peak point of an asymmetric reflection pattern to identify the depth and horizontal position of the underground target. The reflection patterns of the complex shapes due to extreme surface variations results in analysis difficulties. Furthermore, when multiple objects are buried under an undulating ground, it is hard to judge their relative positions based on a B-scan that assumes a flat ground. In this paper, a roots fitting method based on electromagnetic waves (EM) travel time analysis is proposed to take into consideration the realistic undulating ground surface. A wheel-based (WB) GPR and an antenna-height-fixed (AHF) GPR System are presented, and their corresponding fitting models are proposed. The effectiveness of the proposed method is demonstrated and validated through numerical examples and field experiments.Comment: 11 pages, 6 figures, accepted by IEEE TI

Microwave Sensing and Imaging

In recent years, microwave sensing and imaging have acquired an ever-growing importance in several applicative fields, such as non-destructive evaluations in industry and civil engineering, subsurface prospection, security, and biomedical imaging. Indeed, microwave techniques allow, in principle, for information to be obtained directly regarding the physical parameters of the inspected targets (dielectric properties, shape, etc.) by using safe electromagnetic radiations and cost-effective systems. Consequently, a great deal of research activity has recently been devoted to the development of efficient/reliable measurement systems, which are effective data processing algorithms that can be used to solve the underlying electromagnetic inverse scattering problem, and efficient forward solvers to model electromagnetic interactions. Within this framework, this Special Issue aims to provide some insights into recent microwave sensing and imaging systems and techniques