1. Research and practical experience of scanning techniques in Scandinavia;Birkeland,1985
2. Defect detection in lumber: state of the art;Szymani;For. Prod. J.,1981
3. Overview of methods that can be used to measure wood properties;Han,1989
4. Ultrasonics;Cracknell,1980
5. A preliminary test of the use of an ultrasonic pulse technique for detecting and deterioration of telegraph poles;Jones;PSIR Road Res. Lab., Note No. RN 1933-5,1953