This paper introduces a new method of calculating crown projection area(CPA),the area of level ground covered by a vertical projection of a tree crown from measured crown radii through numerical interpolation and inte...This paper introduces a new method of calculating crown projection area(CPA),the area of level ground covered by a vertical projection of a tree crown from measured crown radii through numerical interpolation and integration.This novel method and other four existing methods of calculating CPA were compared using detailed crown radius measurements from 30 tall trees of Eucalyptus pilularis variable in crown size,shape,and asymmetry.The four existing methods included the polygonal approach and three ways of calculating CPA as the area of a circle using the arithmetic,geometric and quadratic mean radius.Comparisons were made across a sequence of eight non-consecutive numbers(from 2 to 16)of measured crown radii for each tree over the range of crown asymmetry of the 30 trees through generalized linear models and multiple comparisons of means.The sequence covered the range of the number of crown radii measured for calculating the CPA of a tree in the literature.A crown asymmetry index within the unit interval was calculated for each tree to serve as a normative measure.With a slight overestimation of 2.2%on average and an overall mean error size of 7.9%across the numbers of crown radii that were compared,our new method was the least biased and most accurate.Calculating CPA as a circle using the quadratic mean crown radius was the second best,which had an average overestimation of 4.5%and overall mean error size of 8.8%.These two methods remained by and large unbiased as crown asymmetry increased,while the other three methods showed larger bias of underestimation.For the conventional method of using the arithmetic mean crown radius to calculate CPA as a circle,bias correction factors were developed as a function of crown asymmetry index to delineate the increasing magnitude of bias associated with greater degrees of crown asymmetry.This study reveals and demonstrates such relationships between the accuracy of CPA calculations and crown asymmetry and will help increase awareness among researchers and practitioners on th展开更多
飞机噪声对机场周围社区的污染是航空环境工程领域的重要问题,限制飞机最大起飞重量(MTOW)或合理规划机场周围社区已成为降低飞机噪声对机场社区噪声污染的2种主要途径。为了实现这2种途径从定性分析向定量研究的转化,对飞机噪声等值线...飞机噪声对机场周围社区的污染是航空环境工程领域的重要问题,限制飞机最大起飞重量(MTOW)或合理规划机场周围社区已成为降低飞机噪声对机场社区噪声污染的2种主要途径。为了实现这2种途径从定性分析向定量研究的转化,对飞机噪声等值线面积与测量点上声暴露级(SEL)之间的准确关系进行了研究。以飞机离场为例,建立了等值线面积与测量点上声暴露级之间关系数学分析模型,利用INM计算的42种机型等值线面积和声暴露级数据,进行了所建模型的合理性和等值线面积与声暴露级之间线性相关性的有效性的验证,得到声暴露级减低1 d B对给定值等值线面积减小的程度或等值线面积按比例减小对噪声级减低的大小。从而为机场周围社区飞机噪声污染定量化控制开辟了新的方法。展开更多
基金supported by the Natural Science Foundation of China (32071758)the Fundamental Research Funds for the Central Universities of China (No. 2572020BA01)
文摘This paper introduces a new method of calculating crown projection area(CPA),the area of level ground covered by a vertical projection of a tree crown from measured crown radii through numerical interpolation and integration.This novel method and other four existing methods of calculating CPA were compared using detailed crown radius measurements from 30 tall trees of Eucalyptus pilularis variable in crown size,shape,and asymmetry.The four existing methods included the polygonal approach and three ways of calculating CPA as the area of a circle using the arithmetic,geometric and quadratic mean radius.Comparisons were made across a sequence of eight non-consecutive numbers(from 2 to 16)of measured crown radii for each tree over the range of crown asymmetry of the 30 trees through generalized linear models and multiple comparisons of means.The sequence covered the range of the number of crown radii measured for calculating the CPA of a tree in the literature.A crown asymmetry index within the unit interval was calculated for each tree to serve as a normative measure.With a slight overestimation of 2.2%on average and an overall mean error size of 7.9%across the numbers of crown radii that were compared,our new method was the least biased and most accurate.Calculating CPA as a circle using the quadratic mean crown radius was the second best,which had an average overestimation of 4.5%and overall mean error size of 8.8%.These two methods remained by and large unbiased as crown asymmetry increased,while the other three methods showed larger bias of underestimation.For the conventional method of using the arithmetic mean crown radius to calculate CPA as a circle,bias correction factors were developed as a function of crown asymmetry index to delineate the increasing magnitude of bias associated with greater degrees of crown asymmetry.This study reveals and demonstrates such relationships between the accuracy of CPA calculations and crown asymmetry and will help increase awareness among researchers and practitioners on th
文摘飞机噪声对机场周围社区的污染是航空环境工程领域的重要问题,限制飞机最大起飞重量(MTOW)或合理规划机场周围社区已成为降低飞机噪声对机场社区噪声污染的2种主要途径。为了实现这2种途径从定性分析向定量研究的转化,对飞机噪声等值线面积与测量点上声暴露级(SEL)之间的准确关系进行了研究。以飞机离场为例,建立了等值线面积与测量点上声暴露级之间关系数学分析模型,利用INM计算的42种机型等值线面积和声暴露级数据,进行了所建模型的合理性和等值线面积与声暴露级之间线性相关性的有效性的验证,得到声暴露级减低1 d B对给定值等值线面积减小的程度或等值线面积按比例减小对噪声级减低的大小。从而为机场周围社区飞机噪声污染定量化控制开辟了新的方法。
