Leaf litter thickness, but not plant species, can affect root detection by ground penetrating radar
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Ground penetrating radar (GPR), a nondestructive tool that can detect coarse tree roots, has not yet become a mature technology for use in forests. In this study, we asked two questions concerning this technology: (i) Does the leaf litter layer influence root detection and major indices based on the time interval between zero crossings (T) and the amplitude area (A)? (ii) Can GPR images discriminate roots of different plant species?
Roots buried in a sandy bed, which was covered with different thicknesses of leaf litter, were scanned using a 900 MHz GPR antenna. Roots of four plant species in the bed were also scanned.
Leaf litter decreased root reflections without distorting the shape of the hyperbolas in the radar profile. A values decreased with increasing litter thickness, whereas T was independent of litter thickness. For all species combined, GPR indices were significantly correlated with root diameter.
Leaf litter dramatically decreased root detection, but the influence of the litter could be ignored when the sum of T for all reflection waveforms (ΣT) is adopted to estimate root diameter. To use A values to detect roots, litter should be removed or equalized in thickness. Radar profiles could not reliably differentiate among roots belonging to plants of different species.
KeywordsCoarse roots Leaf litter Nondestructive root detection Phyllostachys pubescens Root diameter
Sum of amplitude areas for all reflection waveforms
- Single Amax
Amplitude area of the maximum reflection waveform
Time interval between zero crossings
Sum of time intervals for all reflection waveforms
- Single Tmax
Time interval for the maximum reflection waveform
Ground penetrating radar
We thank Y. Kanazawa (Kobe University), M. Ishii and T. Igarashi (KANSO Technos), M. Hiraoka (Tokyo University of Agriculture and Technology), and S. Asano, U. Kurokawa, T. Chikaguchi, S. Narayama, M. Tanaka, Y. Shimada, N. Makita, H. Hagino, and the other members of FFPRI for their help with data analysis and the field experiments. We also thank M. Ohashi (University of Hyogo) and Y. Matsuda (Mie University) for providing comments on an early draft of this manuscript. We additionally thank three reviewers for their critical comments on an earlier draft of the manuscript. We are grateful for financial support from Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan (No. 22380090, 25252027). This study was also supported by the Program for Supporting Activities for Female Researchers, which is funded by MEXT’s Special Coordination Fund for Promoting Science and Technology.
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