Forestry applications of ground-penetrating radar

Abstract

Ground-penetrating radar (GPR) is a geophysical and close-range remote sensing technique based on the use of radar pulses to obtain cross-section images of underground features. This method is characterized by the transmission of an electromagnetic short length pulse (1-2 ns), presenting a centre frequency ranging from 10 MHz to 2.5 GHz. The principles of GPR operation are based on the ability of low frequency radar waves to penetrate into a non-conductive medium, usually subsoil, but also walls, concrete or wood. Those waves are detected after suffering a reflection in electromagnetic discontinuities of the propagation medium. Therefore, this is a suitable method to study changes in those physical properties, and also to characterize different mediums and the reflective targets providing information about their physical properties. The aim of this work is to describe and demonstrate different applications of GPR in forestry, showing the obtained results together with their interpretation. Firstly, in this paper, it is illustrated how GPR is able to map shallow bedrock, subsoil stratigraphy and also to estimate shallow watertable depth. Secondly, different tree trunks as well as dry timber are analyzed, evaluating the different radar data obtained in each particular case, and observing differences in their electromagnetic properties related to the GPR response. Finally, several measurements were taken in order to analyze the use of GPR to detect tree root systems using polarimetric techniques, being possible to detect medium and big size roots, together with groups of small roots.Key words: GPR, remote sensing, bedrock, watertable, trunk, root system. Resumen Aplicaciones forestales del radar de subsueloEl geo-radar o radar de subsuelo (GPR), es una técnica de teledetección cercana que puede emplearse como herramienta de prospección geofísica y que se fundamenta en la emisión de un pulso electromagnético de muy corta duración (1-20 ns) caracterizado por una frecuencia central que puede variar entre los 10 MHz y los 2,5 GHz, en función de la antena seleccionada. Tras su emisión mediante una antena transmisora, las ondas de radar experimentan reflexiones en las discontinuidades electromagnéticas existentes en el medio por el que se propagan, siendo detectadas por una segunda antena receptora. El análisis de las reflexiones puede utilizarse para caracterizar tanto el medio de propagación como los reflectores, por lo que resulta un método adecuado para el estudio de determinadas propiedades físicas. El objetivo principal de este trabajo es mostrar diferentes aplicaciones del GPR en el ámbito forestal. Para ello se exponen los fundamentos básicos del método y su aplicabilidad como herramienta versátil en el ámbito forestal, así como posibles resultados que se pueden obtener en casos concretos. Como primera aplicación se presentan dos ejemplos que ilustran la capacidad de este método para detectar sustratos rocosos a poca profundidad, para analizar la estratigrafía superficial de un suelo y para localizar el n...

Application of ground penetrating radar for coarse root detection and quantification: a review

“…Hruška et al (1999) first applied GPR technique for coarse root detection and claimed that GPR was an appropriate tool for coarse root mapping. The major interests of using GPR to detect coarse root thus far include: 1) coarse root mapping (e.g., Hruška et al 1999;Čermák et al 2000;Wielopolski et al 2000;Stokes et al 2002;Cox et al 2005;Samuelson et al 2008;Zenone et al 2008;Schoor and Colvin 2009;Leucci 2010;Bassuk et al 2011); and 2) coarse root biomass and diameter estimation (e.g., Butnor et al 2001Butnor et al , 2003Barton and Montagu 2004;Butnor et al 2005;Cox et al 2005;Stover et al 2007;Butnor et al 2008;Samuelson et al 2008;Dannoura et al 2008;Hirano et al 2009;Lorenzo et al 2010;Cui et al 2011). In what follows, each of the applications is comprehensively reviewed.…”

“…They concluded that many aspects of GPR hardware, visualization software, and signal processing methods need to be improved before precise 3D root system images could be reconstructed from radargrams. Due to the difficulty of root 3D architecture reconstruction, some studies (e.g., Lorenzo et al 2010;Leucci 2010) attempted to apply GPR to resolve root-zone (i.e., the region of soil located in and around the root system) in 2D/3D rather than accurately locate single coarse root. In these studies, GPR was used to scan root systems in a grid (consisting of different parallel lines in both x and y directions).…”

“…Wave velocity can be obtained from the following equation (Lorenzo et al 2010): where μ is the magnetic permeability, σ is the electrical conductivity, ε is the dielectric permittivity, and ω is the angular frequency (i.e., ω02π f, where f is frequency) of the emitted pulse. For low conductive and nonmagnetic materials (i.e., σ < < ωε and μ r 01, where μ r is the relative magnetic permeability), propagation velocity can be estimated by the formula (al Hagrey 2007):…”

A Method for Layered Identification of Defects in Trees Using Ground Penetrating Radar

“…When the pulses encounter subsurface interfaces or boundaries with different dielectric constants, the reflections are different. The internal defects have a different dielectric constant from that of surrounding wood [5]. Thus, the research is able to deduce the location of the internal defects of tree and make the defects layered recognition based on the properties.…”

“…In recent years, scholars also gradually take GPR for trees detection seriously. Studies pointed out that these anomalies could be associated the inner discontinuities between the bark and the internal trunk and lower velocities correspond to living trees, while higher velocities are associated with timber [5]. Other studies located the position of internal defects and the algorithm for identifying the defects in wooden logs using GPR [6]; some others showed relations between relative permittivity and moisture content of the different wood samples [7].…”