Ground‐Penetrating Radar Detection and Three‐Dimensional Mapping of Lateral Macropores: I. Calibration

Abstract

Preferential flow of water through soil macropores is known to contribute to groundwater and surface water contamination as well as stream bank instability. However, research on the mechanisms and extent of soil macroporosity is limited due to the lack of a practical technique to study macropores in situ without disrupting the site's ecological function. In this paper, we present a ground‐penetrating radar (GPR)‐based methodology for detecting soil macropores smaller than 10 cm in diameter within 1 m of the soil surface and then creating a computerized tomogram of the macropore network. Manual and automated algorithms for macropore detection were tested for scan data collected using a 900‐MHz radar antenna in a field experiment with a silt‐loam soil. Buried polyvinyl chloride (PVC) pipes were used to simulate soil macropores of different diameters and fill contents intersected by GPR scan lines at four different angles. Pipes ≥ 3.00 cm in diameter were clearly detectable regardless of the scan line orientation relative to the target, and pipes with diameters as small as 1.85 cm were detected at perpendicular angles of intersection. In a second field experiment, PVC pipes of varying dimensions were buried at different depths to simulate a macropore network of preferential flow pathways. A branch‐node algorithm was developed that referenced GPR scan line detections to create an accurate computer‐generated three‐dimensional map of the pipe network.

Using Ground-Penetrating Radar to Detect Tree Roots and Estimate Biomass

“…This trait is used in an inferential way to determine root health in urban root inspections. Even roots located in high water table soils are may be detectable (Gormally et al 2010). Although living roots are detectable, it may only be possible to estimate a bulk property of the roots structure such as root density.…”

The relevance of preferential flow in catchment scale simulations: Calibrating a 3D dual‐permeability model using DREAM

“…In situ detection of macropores by destructive sampling after dye tracing (e.g., Anderson, Weiler, Alila, & Hudson, ; Graham, Woods, & McDonnell, ; Laine‐Kaulio, Backnäs, Koivusalo, & Lauren, ; Weiler & Naef, ) or non‐invasive techniques, such as ground‐penetrating radar (Gormally, McIntosh, & Mucciardi, ; Gormally, McIntosh, Mucciardi, & McCarty, ; Nyquist, Toran, Pitman, Guo, & Lin, ), have shown a ubiquitous presence of macropores in different landscapes. Due to this widespread evidence of preferential flow in the subsurface, it seems necessary to represent macropores in hydrological models in order to advance the understanding of subsurface flow behaviour and hydrological threshold processes, catchment runoff generation, leaching of nutrients and contaminants and slope stability mechanisms with related landslide risks (e.g., Klaus & Zehe, ; Roulier et al, ; Shao, Bogaard, & Bakker, ; Shao, Bogaard, Bakker, & Greco, ; Weiler & McDonnell, ; Zehe, Becker, Bárdossy, & Plate, ).…”

A Novel Method of Hyperbola Recognition in Ground Penetrating Radar (GPR) B-Scan Image for Tree Roots Detection

“…The water content is one of the important factors affecting the relative dielectric constant of the medium [12]. In this study [70], the pipes which contained water, a 1:1 ratio of water and air, air, and salt water (22 mg cm −3 iodized sea salt) were detected in the designed controlled experiments. A small difference in relative dielectric permittivity between moist soil and root affected root detection.…”