Abstract
The tree sway frequency is an important part of the dynamic properties of trees. In order to obtain trees sway frequency in wind, a method of tracking and measuring the sway frequency of leafless deciduous trees by adaptive tracking window based on MOSSE was proposed. Firstly, an adaptive tracking window is constructed for the observed target. Secondly, the tracking method based on Minimum Output Sum Of Squared Error Filter (MOSSE) is used to track tree sway. Thirdly, Fast Fourier transform was used to analyze the horizontal sway velocity of the target area on the trees, and the sway frequency was determined. Finally, comparing the power spectral densities (PSDs) of the x axis acceleration measured by the accelerometer and PSDs of the x axis velocity measured by the video, the fundamental sway frequency measured by the accelerometer is equal to the fundamental sway frequency measured by video. The results show that the video-based method can be used successfully for measuring the sway frequency of leafless deciduous trees.
Highlights
Wind has an important influence on a single tree or whole forest stands and is one of the main causes of forest disasters
From a comparison with the measurement results of the accelerometer, it can be seen that the frequency of the target can be identified by Fast Fourier transform (FFT) analysis of the motion signal of the target based on the video, which is comparable with the measurement results of the accelerometer
An adaptive tracking window is constructed based on the Minimum Output Sum Of Squared Error Filter (MOSSE) algorithm, and a method for tracking and measuring the frequency of leafless deciduous tree sway is established; the fundamental mode of the tree sway is analyzed
Summary
Wind has an important influence on a single tree or whole forest stands and is one of the main causes of forest disasters. The tree sway frequency is an important part of the dynamic properties of trees. Researchers have conducted a number of outdoor experiments to measure tree sway frequencies, which can be divided into two types depending on the source of the tree’s vibration excitation. When the trees is released, the free motion of the trees is recorded. This type of experiment is commonly called a “pull test” [8]. The second is the tracking of sway motion under natural wind conditions, which can truly reflect the dynamic properties of trees [6,7,9,10,11]. A method that can measure tree sway in the wind is of great significance to understand the dynamic properties of trees
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