Joakim Axmon

Blind Impact Response Analysis for Health Assessment of Living Trees

Abstract

Culture of common spruce is of importance for the Scandinavian
forestry industry. Unfortunately, spruce is highly susceptible to
fungal pathogens causing rot and decay of the inner tissues of trunks,
rendering the wood useless for construction material, and ultimately
even for pulp. When assessing the value of a forest stand, it is
therefore critical to know the ratio of trees in decay. Since there
are no definite external signs of decay, a number of tools have been
proposed over the years. In this talk, an experimental non-destructive
technique based on two-dimensional frequency analysis of impact
responses, is addressed. The technique, which is related to
traditional sounding, relies on the fact that decay alters the
mechanical properties of wood. Trees in decay are therefore expected
to exhibit lower resonance frequencies than sound trees of matching
dimensions.  The talk is focused towards joint two-dimensional
frequency estimation using state-space/subspace rotation, but issues
related to the field of application, such as phytopathological
background and techniques for detection of decay, are addressed as
well.

Keywords: Array signal processing, X-texture modes, ESPRIT, partial
forward-backward averaging, frequency pairing