Reply to: “Comment on root orientation can affect detection accuracy of ground-penetrating radar”
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We showed that root orientation affected a parameter of ground penetrating radar (GPR), amplitude area (A) (Tanikawa et al. Plant Soil 373:317–327, 2013). The aims of this reply to Wu et al. (2014) are (i) to correct the two inaccuracies in Tanikawa et al. (2013) and (ii) to improve our method of estimating A(90°) using A(x) of root angle x.
Measured A values of Tanikawa et al. (2013) were analyzed with the modified equations.
The first inaccuracy was the use of incorrect units for the coefficient b (the phase shift) in the sinusoidal waveform of A(x). The units should have been radians instead of degrees. The second inaccuracy was the mis-derivation of A(x) into A(x + 90°). In the modified method, A(90°) was estimated by A(x) from two orthogonally intersecting transect lines and a transect line at a diagonal to them.
The two inaccuracies did not affect the previous main conclusions that the parameter T was suitable for estimating root diameter and that grid transects are likely to identify clear hyperbolas reflecting roots in radar profiles (Tanikawa et al. 2013). By the improved method, we could accurately estimate root diameter by scanning using three transect lines intersecting at angles of x, x + 45°, and x + 90°.
KeywordsCarbon storage Coarse root Grid transects Nondestructive measurement Root angle Root diameter
Root angle subtended to the transect lines
The maximum value of A(x) reflecting root diameter
Sum of amplitude areas for all of reflection waveforms
Amplitude area of the maximum reflection waveform
Time interval between zero crossings
Sum of time intervals for all reflection waveforms
We thank Y. Matsuda for reviewing a draft of this manuscript. We additionally thank the editor and two anonymous reviewers for their constructive comments on an earlier draft of the manuscript. We acknowledge financial support from the Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (No. 22380090, 25252027). This work was also supported by the Program for Supporting Activities for Female Researchers funded by MEXT’s Special Coordination Fund for Promoting Science and Technology.
- Wu Y, Guo L, Li W, Cui XH, Chen J (2014) Comment on: “root orientation can affect detection accuracy of ground-penetrating radar”. Plant Soil. doi: 10.1007/s11104-014-2124-7