Quantification of knots in dimension lumber using a single-pass X-ray radiation

The knot depth ratio (KDR) evaluation method was designed to quantitatively evaluate the amount of knot in dimension lumber by a single-pass X-ray radiation. To verify the proposed method, KDR values for 38-mm-thick specimens were predicted, and they were compared with the actual measured KDR values. The knot is surrounded by the transition zone, and the density of the knot and the transition zone is higher than the clear wood. Because the average density of the transition zone was similar to the knot density, it was found that the proposed method gives the KDR values for the knot area including the transition zone. The coefficients of determination between the predicted and measured KDR values were 0.87 and 0.83 for Japanese larch and red pine specimens, respectively. Using the KDR information, the ratio of knot area including transition zone to cross-sectional area was calculated. The presence of latewood and earlywood in the same path of the X-ray radiation caused discrepancies in the estimation of KDR values because the density of latewood is much higher than that of earlywood. Fortunately, latewood and earlywood are repeated in a cross section, so the amount of overestimation and underestimation was expected to be nearly identical. As expected, the relationship between the predicted area ratio and the real area ratio of knot and transition zone was strong with R**2 values of 0.89 and 0.93 for Japanese larch and red pine specimens, respectively