Experimental Evaluation of Several Key Factors Affecting Root Biomass Estimation by 1500 MHz Ground-Penetrating Radar

Accurate quantification of coarse roots without disturbance represents a gap in our understanding of belowground ecology. Ground penetrating radar (GPR) has shown significant promise for coarse root detection and measurement, however root orientation relative to scanning transect direction, the difficulty identifying dead root mass, and the effects of root shadowing are all key factors affecting biomass estimation that require additional research. Specifically, many aspects of GPR applicability for coarse root measurement have not been tested with a full range of antenna frequencies. We tested the effects of multiple scanning directions, root crossover, and root versus soil moisture content in a sand-hill mixed oak community using a 1500 MHz antenna, which provides higher resolution than the oft used 900 MHz antenna. Combining four scanning directions produced a significant relationship between GPR signal reflectance and coarse root biomass (R2 = 0.75) (p \u3c 0.01) and reduced variability encountered when fewer scanning directions were used. Additionally, significantly fewer roots were correctly identified when their moisture content was allowed to equalize with the surrounding soil (p \u3c 0.01), providing evidence to support assertions that GPR cannot reliably identify dead root mass. The 1500 MHz antenna was able to identify roots in close proximity of each other as well as roots shadowed beneath shallower roots, providing higher precision than a 900 MHz antenna. As expected, using a 1500 MHz antenna eliminates some of the deficiency in precision observed in studies that utilized lower frequency antennas

GPR applications in mapping the subsurface root system of street trees with road safety-critical implications

Street trees are an essential element of urban life. They contribute to the social, economic and environmental development of the community and they form an integral landscaping, cultural and functional element of the infrastructure asset. However, the increasing urbanisation and the lack of resources and methodologies for the sustainable management of road infrastructures are leading to an uncontrolled growth of roots. This occurrence can cause substantial and progressive pavement damage such as cracking and uplifting of pavement surfaces and kerbing, thereby creating potential hazards for drivers, cyclists and pedestrians. In addition, neglecting the decay of the principal roots may cause a tree to fall down with dramatic consequences. Within this context, the use of the ground-penetrating radar (GPR) non-destructive testing (NDT) method ensures a non-intrusive and cost-effective (low acquisition time and use of operators) assessment and monitoring of the subsurface anomalies and decays with minimum disturbance to traffic. This allows to plan strategic maintenance or repairing actions in order to prevent further worsening and, hence, road safety issues. This study reports a demonstration of the GPR potential in mapping the subsurface roots of street trees. To this purpose, the soil around a 70-year-old fir tree was investigated. A ground-coupled GPR system with central frequency antennas of 600 MHz and 1600 MHz was used for testing purposes. A pilot data processing methodology based on the conversion of the collected GPR data (600 MHz central frequency) from Cartesian to polar coordinates and the cross-match of information from several data visualisation modes have proven to identify effectively the three-dimensional path of tree roots

Application of Ground-Penetrating Radar in measuring Corn seeds (CS) Spacing and Planting depth in different soils

The effects of seed spacing and depth at planting contribute greatly to corn production. Correct seed spacing, and planting depth may enable moisture absorption which facilitates seedling emergence with the establishment of healthy and robust root structure. Therefore, measuring seed spacing and planting depths in a closed furrow is necessary for precision seeding and corn production. In agricultural applications, Ground Penetrating Radar (GPR) is used for nondestructive evaluations as a potential sensor to maximize the qualitative and precision or repeatable assessments in long-term research. Yet GPR system has not been used to measure seed spacing and planting depths, but it has the potential to measure the two parameters. The objective of this experimental research was to use a non-destructive 2.6 GHz GPR system to detect agricultural Corn Seeds (CS) buried at different depths (3.81, 6.35, and 8.89 cm) and spacing (15.24 and 25.4 cm) in sandy-loam and loam soils. The data was processed using the Fast Discrete Curvelet Transform to denoise and enhance edge responses from CS. In bone-dry soils some CS were detected, while in intermediate and moist soils it was difficult to detect CS. The two-way travel time in nanoseconds and soil dielectric permittivity from experimental data were used to estimate planting depth while the spatial distance between the CS was computed from the antenna cart encoder. The Topp‘s dielectric, soil mixing, and the Topp-Mixing (TM) model were used to estimate the soil dielectric permittivity. The TM model was developed as a function of the Topp‘s dielectric, and soil mixing models to minimize and optimize planting depth error (PDE). The TM model was found to be effective in predicting permittivity used to approximate planting depth with minimal PDE. The assessment of the 2.6 GHz antenna effectiveness was based on the percent coefficient of precision (CP3) and coefficient of planting depth accuracy (CPDA). The CP3 values were \u3c 30% but differed for the three moisture groups and soil types. The TM model had the best CPDA of 9.9%. While the results are promising, more research is needed to enable detection and depth measurements of CS in soil conditions that are typical of a ploughed field

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

An enhanced data processing framework for mapping tree root systems using ground penetrating radar

The preservation of natural assets is nowadays an essential commitment. In this regard, root systems are endangered by fungal diseases which can undermine the health and stability of trees. Within this framework, Ground Penetrating Radar (GPR) is emerging as a reliable non-destructive method for root investigation. A coherent GPR-based root-detection framework is presented in this paper. The proposed methodology is a multi-stage data analysis system that is applied to semi-circular measurements collected around the investigated tree. In the first step, the raw data are processed by applying several standard and advanced signal processing techniques, to reduce noise-related information. In the second stage, the presence of any discontinuity element within the survey area is investigated by analysing the signal reflectivity. Then, a tracking algorithm aimed at identifying patterns compatible with tree roots is implemented. Finally, the mass density of roots is estimated by means of continuous functions, to achieve a more realistic representation of the root paths and to identify their length in a continuous and more realistic domain. The method was validated in a case study in London (UK), where the root system of a real tree was surveyed using GPR and a soil test pit was excavated for validation purposes. Results support the feasibility of the data processing framework implemented in this study

Mapping and assessment of tree roots using ground penetrating radar with low-cost GPS

In this paper, we have presented a methodology combining ground penetrating radar (GPR) and a low-cost GPS receiver for three-dimensional detection of tree roots. This research aims to provide an effective and affordable testing tool to assess the root system of a number of trees. For this purpose, a low-cost GPS receiver was used, which recorded the approximate position of each GPR track, collected with a 500 MHz RAMAC shielded antenna. A dedicated post-processing methodology based on the precise position of the satellite data, satellite clock offsets data, and a local reference Global Navigation Satellite System (GNSS) Earth Observation Network System (GEONET) Station close to the survey site was developed. Firstly, the positioning information of local GEONET stations was used to filter out the errors caused by satellite position error, satellite clock offset, and ionosphere. In addition, the advanced Kalman filter was designed to minimise receiver offset and the multipath error, in order to obtain a high precision position of each GPR track. Kirchhoff migration considering near-field effect was used to identify the three-dimensional distribution of the root. In a later stage, a novel processing scheme was used to detect and clearly map the coarse roots of the investigated tree. A successful case study is proposed, which supports the following premise: the current scheme is an affordable and accurate mapping method of the root system architecture

Coarse Root Biomass and Architecture: Applications of Ground Penetrating Radar

The effectiveness of ground penetrating radar (GPR) to identify and quantify coarse roots was tested in a mixed-oak forest in Southeastern Virginia using experimental pits and locally excavated root segments. GPR was found to be highly dependent on low soil moisture levels as it is unable to differentiate root structures if they possess similar moisture content as their surrounding soil. Likewise, GPR was unable to identify simulated dead roots. This does not alter the effectiveness of GPR to measure living coarse root biomass, but does present the potential for underestimation of carbon storage in coarse root structures, as a dead roots continue to store carbon. GPR was able to recognize and quantify increasing root density suggesting an ability to quantify change in root mass over time, but it was not able to reliably represent changes in root diameter. Coarse root biomass estimation using GPR was conducted using a grid scanning technique applied to sample plots located within multiple systems. GPR effectively measured coarse root biomass across multiple systems, showing no significant difference between estimated and observed coarse root biomass in a Virginia mixed-oak forest ecosystem, a Florida scrub-oak ecosystem, or a Florida longleaf pine flatwoods ecosystem. GPR appears to have difficulty with root structures near the surface, as it is not able to reliably separate these structures from the soil-air interface. Post-experimental disturbance effects were examined in a Florida scrub-oak ecosystem, following an 11-year open-top chamber elevated CO2 experiment that concluded in 2006 and had been abandoned for seven years. Aboveground harvest showed a significantly higher regrowth two years post fire in previously elevated CO2 plots when compared with plots that were kept at ambient CO2 levels throughout the duration of the original experiment. No significant difference was found in coarse root biomass between the two treatments; however, a non-significant trend of 12% higher biomass in the previously elevated CO2 plots was found that coincided with a similar trend observed during the original experiment. Long-lasting effects of elevated CO2 appear to exist within this system, indicating an ability for plants to store additional carbon and to regrow more rapidly following fire disturbance. Carbon storage within coarse roots was examined in a Florida longleaf pine flatwoods ecosystem as part of a larger, ongoing effort to quantify total carbon storage and flux within multiple systems relative to longleaf pine restoration. Coarse root carbon storage was estimated at 3.5 – 3.7 kg C/m2, suggesting large carbon storage potential associated with longleaf pine restoration. GPR is an effective, non-destructive tool for quantifying coarse root biomass and an effective but limited tool for determining root architecture. Both applications of GPR are highly dependent on user-determined settings during data collection and post-collection processing, thus effective GPR application is highly dependent on the level of familiarity possessed by the operator

Evaluating tree root distribution in a tree-based intercropping system with use of ground penetrating radar

Paper presented at the 13th North American Agroforesty Conference, which was held June 19-21, 2013 in Charlottetown, Prince Edward Island, Canada.In Poppy, L., Kort, J., Schroeder, B., Pollock, T., and Soolanayakanahally, R., eds. Agroforestry: Innovations in Agriculture. Proceedings, 13th North American Agroforestry Conference, Charlottetown, Prince Edward Island, Canada, June 19-21, 2013.Within agroforestry systems, tree root architecture is a driver of important ecological processes such as belowground nutrient flows and C storage. Yet the belowground component of trees remains largely under-studied due to methodological restraints. Conventional subsurface sampling can overlook the heterogeneity of root systems, while complete excavations are destructive and unrepeatable. Thus, there is a need to develop non-intrusive technologies, such as ground penetrating radar (GPR), to measure root systems in situ. In this study we used GPR to detect coarse root distributions below five tree species (Quercus rubra, Juglans nigra, Populus sp., Picea abies, and Thuja occidentalis) at a temperate tree-based intercropping site in Guelph, Ontario. GPR geo-imaged transects were collected in 4.5 _ 4.5m grids that were centered on 15 individual trees. Subsequently, tree roots were identified across all geo-images (visualized as radar signal reflections) providing 3-dimensional root distribution data for each target tree. Roots detected by GPR accounted for approximately 80% of large coarse roots (�1cm) and 40% of small coarse roots (<1cm) that were later exposed in a subset of matched soil profiles. Significant inter-specific variations of coarse rooting depth preferences were detected. Additionally, preliminary analyses indicate different tree rooting patterns below the crop rows. To determine fine root distributions, fine roots were extracted from soil cores collected from the tree root study plots. Preliminary analysis indicates fine root length densities vary across species predominately in the upper 20cm. Limitations will be identified and applications will be discussed of GPR to answer ecological questions within agroforestry systems. Notably, we will highlight results from our complementary study that used the same GPR data to effectively estimate belowground biomass.Kira A. Borden (1), Marney E. Isaac (2) and Sean C. Thomas (1) ; 1. Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Ontario, Canada, M5S 3B3. 2. Department of Physical and Environmental Sciences, University of Toronto at Scarborough, 1265 Military Trail, Toronto, Ontario, Canada, M1C 1A4.Includes bibliographical references