3D Ground Penetrating Radar to Detect Tree Roots and Estimate Root Biomass in the Field

Shiping Zhu,Yi Su,Motoyuki Sato,Chunlin Huang

doi:10.3390/rs6065754

Abstract

The objectives of this study were to detect coarse tree root and to estimate root biomass in the field by using an advanced 3D Ground Penetrating Radar (3D GPR) system. This study obtained full-resolution 3D imaging results of tree root system using 500 MHz and 800 MHz bow-tie antennas, respectively. The measurement site included two larch trees, and one of them was excavated after GPR measurements. In this paper, a searching algorithm, based on the continuity of pixel intensity along the root in 3D space, is proposed, and two coarse roots whose diameters are more than 5 cm were detected and delineated correctly. Based on the detection results and the measured root biomass, a linear regression model is proposed to estimate the total root biomass in different depth ranges, and the total error was less than 10%. Additionally, based on the detected root samples, a new index named “magnitude width” is proposed to estimate the root diameter that has good correlation with root diameter compared with other common GPR indexes. This index also provides direct measurement of the root diameter with 13%–16% error, providing reasonable and practical root diameter estimation especially in the field.

Highlights

Ground Penetrating Radar (GPR), as a convenient, nondestructive technique to acquire subsurface information, has been successfully used in many engineering applications in detection and localization of subsurface targets [1,2,3,4]
The three-dimensional (3D) views were delineated manually based on the different GPR profiles after signal processing, it still verified the feasibility of the GPR technique for root detection
Root biomass estimation using GPR can be classified as two kinds of approaches [10]: one is to estimate the coarse root biomass from the GPR reflection intensity indexes directly; the other is to estimate the diameter of the coarse root first, and combine prior information of root density to calculate the root biomass indirectly

Summary

Introduction

Ground Penetrating Radar (GPR), as a convenient, nondestructive technique to acquire subsurface information, has been successfully used in many engineering applications in detection and localization of subsurface targets (e.g., landmine, pipelines, and cables) [1,2,3,4]. The scanning grids usually were too sparse in the measurements to satisfy the Nyquist spatial sampling criterion, which would result in spatial aliasing of the 3D migrated results These above-mentioned studies demonstrated that only coarse roots could be detected and the clustering of fine roots was not detectable individually in the field. For the first kind of approach, some indexes usually calculated from the GPR profiles after migration and Hilbert transform were validated to correlate with the root biomass, which include areas within threshold range, pixels within threshold range, mean pixel intensity, high amplitude area, and so on [15,16,17]. The GPR technique becomes more and more popular, and widely-used in the study of tree root systems, which has been an important application of GPR [21,22,23,24,25,26]

Objectives

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Results

Conclusion