Arboriculture & Urban Forestry 37(5): September 2011 CONCLUSIONS The results of this feasibility study showed that classification based on several vibration waveform statistics was able to detect decay in trunk segments of a wide range of urban tree species. The authors believe this research establishes the feasibility of using an electro-mechanical instrument to replicate the trained human ear. This accelerometer system is a fundamentally different and novel concept in the context of existing velocity-based instrumented systems. Compared to a human operator, the advantages of the instrument are that it operates at a much higher sensitivity to fre- quencies of interest, does not lose its frequency discrimination over time, and is insensitive to ambient noise. If its application is as successful for standing mature trees as with the tested trunk segments, it has the potential for being used by arborists to iden- tify trees that should be subjected to more detailed inspection. This work provides only preliminary evidence that the meth- od and protocol described herein may have value as an initial decay detection tool. The authors recognize there is a big step from this feasibility test to real world application involving standing trees, including various influences of trunk geom- etry, moisture, temperature, and material properties. Future work will focus on testing additional trunk samples, establish- ing the distance at which decay can be detected from the lo- cation of the hammer strike, and determining the effects of standing trees versus felled segments. Furthermore, the authors plan to construct an electro-mechanical complete system pro- totype for classifying samples in real-time on standing trees. Acknowledgments. The authors wish to thank Mr. Pogo Sherwood (Pogo Tree Experts, Olney, MD, U.S.) for his expertise and help in locat- ing and preparing the tree samples and for making his facilities available for our experimental data collection purposes. The authors also wish to thank Dr. Colin Ratcliffe (U.S. Naval Academy, Dept. of Mechanical En- gineering, Annapolis, MD, U.S.) for providing the accelerometer data acquisition instrumentation and for his assistance in the field collecting data. The authors gratefully acknowledge the AUF reviewers who greatly enhanced this paper with their constructive comments. LITERATURE CITED Axmon, J., M. Hansson, and L. Sörnmo. 2004. Experimental Study on the Possibility of Detecting Internal Decay in Standing Picea abies by Blind Impact Response Analysis. Forestry 77(3):179–192. Figure 7. Distribution of all sample lengths, diameters, and spe- cies showing a lack of classifier bias. a) Distribution of trunk length versus diameter. b) Distribution of trunk species versus diameter. separate the “decayed” and “non-decayed” classes was consis- tent with Lufti (2001), who showed that several acoustic param- eters were necessary to aurally classify a hollow bar in labora- tory conditions. The acoustic structures described by the three statistical features were also related to the acoustics used by ar- borists to classify the trunk segments with sounding: the char- acteristic “thud” sound of hollow trees is shown in Figure 3 as long-duration low-frequency reverberation (slow wave modula- tion in the sonic waveform) that is also reflected in the cumu- lative power, pulse duration, and amplitude kurtosis features. Ballas, J.A. 1993. Common Factors in the Identification of an Assortment of Brief Everyday Sounds, Journal of Experimental Psychology. Hu- man Perception and Performance 19:250–267. Boyce, J.S. 1961. Forest Pathology. 3rd Edition. McGraw-Hill Book Company, New York. Brashaw, B.K., V. Bucur, F. Divos, R. Goncalves, J. Lu, R. Meder, R.F. Pellerin, S. Potter, R.J. Ross, X. Wang, Y. Yin. 2009. Nondestructive Testing and Evaluation of Wood: A Worldwide Research Update. Forest Products Journal 59 (37):7–14. Bucur, V. 2003. Nondestructive Characterization and Imaging of Wood. Springer-Verlag, Berlin. Bucur, V. 2005. Ultrasonic techniques for nondestructive testing of stand- ing trees. Ultrasonics 43:237–239. Fowler, C.A., and L.D. Rosenblum. 1990. Duple 1990. Duplex Perception: A Compar- ison of Monosyllables and Slamming Doors. Journal of Experimental Psychology. Human Perception and Performance 16:742–754. 197 ©2011 International Society of Arboriculture
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