سابِق|تال

Influences of semiellipsoid-shaped crown on gap fraction and clumping index

  • role： First author第一作者
  • Affiliation：

    College of Civil Engineering, Hefei University of Technology, Hefei 230009, China

    Intelligent Interconnected Systems Laboratory of Anhui Province (Hefei University of Technology), Hefei 230009, China

  • Email：wangshaoteng1995@163.com
  • Introduction：王少腾，1995年生，男，硕士研究生，研究方向为植被定量遥感。E-mail： wangshaoteng1995@163.com
WANG Shaoteng12,  
  • role： Corresponding author通信作者
  • Affiliation：

    College of Civil Engineering, Hefei University of Technology, Hefei 230009, China

    Intelligent Interconnected Systems Laboratory of Anhui Province (Hefei University of Technology), Hefei 230009, China

  • Email：gengj@hfut.edu.cn
  • Introduction：耿君，1988年生，男，讲师，研究方向为植被定量遥感。E-mail： gengj@hfut.edu.cn
GENG Jun12*,  
  • Affiliation：

    School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China

TU Lili3,  
  • Affiliation：

    Faculty of Geosciences and Environment Engineering, Southwest Jiaotong University, Chengdu 611756, China

YIN Gaofei4

ملخص

The structural characteristics of forest canopy directly affect the radiation interception of forest, which in turn affect the energy exchange between the canopy and the external environment. As an important part of forest canopy structure, crown shape is greatly important for calculating the gap fraction and clumping index. Researchers have calculated gap fraction and clumping index by simulating crown shape as basic geometry, such as cone, cylinder, and cone + cylinder. However, the growth of the crown is influenced by factors, such as external environment and internal apical dominance, resulting in the semiellipsoid shape of the crown. The semiellipsoid is more consistent with the natural growth low of the crowns than these crown shapes. In fact, the semiellipsoid is a very common crown shape, which is significantly different from other crown shapes with an important influence on the calculation of canopy structure parameters, such as the gap fraction of canopies and clumping index. The main objective is to exhibit the influence of the semiellipsoid-shaped crown on the gap fraction and clumping index of forest canopies.First, assuming that the crown is an opaque geometric entity with the Poisson distribution in space, the gap fraction on crown scale was calculated. Second, considering that gaps exist in an individual crown, the formula for calculating the gap fraction of an individual crown was introduced. Then, crowns with semiellipsoid and double semiellipsoid shapes were applied to the formula of gap fraction of canopies and clumping index. Meanwhile, considering the semiellipsoid-shaped crown as the calculation criterion, we analyzed the relative differences of gap fraction of canopies and clumping index with different crown shapes. The main input parameters included crown density, crown height, crown radius and leaf area index. Finally, the results were verified by virtual scenes.The results indicated that: (1) the gap fraction of canopies between the semiellipsoid-shaped crown and crowns with other shapes was relatively different. With the increment of view zenith angle, the relative differences of gap fraction between the semiellipsoid-shaped crown and crowns with other shapes increased. When the view zenith angle was 70°, the relative difference of gap fraction between the cone-shaped crown and the semiellipsoid-shaped crown was close to 100%. (2) The crown shape also had a significant influence on the clumping index. In extreme cases, the relative differences of clumping index between the cone-shaped crown and the semiellipsoid-shaped crown reached up to 30%. In addition, different crown densities had an important effect on the clumping index of different crown shapes. With the decrease in crown density, the relative difference in the clumping index of the semiellipsoid-shaped crown and crowns with other shapes showed an increasing trend. (3) When calculating the expectation value of the clumping index in the hemisphere space, the value of the cylinder-shaped crown was approximately 13% higher than the value of the semiellipsoid-shaped crown, and the value of the semiellipsoid-shaped crown was approximately 22% higher than that of cone-shaped crown. The value of the semiellipsoid-shaped crown and double semiellipsoid-shaped crown was close to each other, and the mixture of two crown shapes slightly influenced the results.Therefore, the semiellipsoid-shaped crown should be considered when studying the structural characteristics of forest canopy, such as gap fraction and clumping index.

مفهوم

remote sensing;crown shape;semi-ellipsoid-shaped crown;double semi-ellipsoid-shaped crown;gap fraction;clumping index

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