Root orientation can affect detection accuracy of ground-penetrating radar

Ground-penetrating radar (GPR) has been applied to detect coarse tree roots. The horizontal angle of a root crossing a scanning line is a factor that affects both root detection and waveform parameter values. The purpose of this study was to quantitatively evaluate the influence of root orientation (x, degree) on two major waveform parameters, amplitude area (A, dB x ns) and time interval between zero crossings (T, ns). We scanned four diameter classes of dowels in a sandy bed as simulated roots using a 900 MHz antenna from multiple angles to clarify the relationships between the parameters and x. Angle x strongly affected reflection images and A values. The variation in A(x) fitted a sinusoidal waveform, whereas T was independent of x. The value of A scanning at 90A degrees was estimated by A values of arbitrary x in two orthogonal transects. The sum of T in all reflected waveforms showed a significant linear correlation with dowel diameter. We clarified that root orientation dramatically affected root detection and A values. The sum of T of all reflected waveforms was a suitable parameter for estimating root diameter. Applying grid transects can overcome the effects of root orientation.