Effect of wood log shape on moisture content measurement using GPR

Non-destructive real time sensors such as GPR based instruments are being used within the forest products industry. GPR based sensors have been used to measure moisture content in cylindrical wood logs using both early time signal amplitude and total travel time. The physical size of the logs may be close to the antenna size and the wavelength and the GPR center frequency in some cases. It is important to have an understanding about the impact of log diameter on measurement accuracy and to know the log size limitations. We have used numerical modelling to estimate the errors that can occur. For measurements performed on the side of the log the, surface curvature results in variable gaps between the GPR antenna and the surface of the log. For measurements performed on the ends of the log, the presence of the cylindrical sides of the log close to the antennas also affect the propagation. The numerical modelling shows there are significant errors in early time amplitude and travel time for small log diameters that will affect the inferred moisture content.