荒漠灌木侧影面积的数字化测定及应用

植株侧影面积是评价其防风固沙效能的重要指标,同时在植被粗糙元密集度计算中,如何得到更准确的侧影面积是急需解决的问题。为了尝试采用数字图像法对3种荒漠灌木进行了测量,重点探讨影响测定结果的因素,比较了数字图像法与其他2种方法的优劣,并初步分析了侧影面积、冠幅与疏透度三者之间的关系。结果表明:与其他2种方法相比,数字图像法操作相对复杂,测定结果稳定性相对较差,但避免了枝叶间的大量孔隙,测得的侧影面积更接近真实值;参照物面积与相机焦距对测定结果影响不显著,而参照物位置、拍摄角度与容差则相反,背景干扰是影响测定结果的一个重要因素;3种荒漠灌木的冠幅与其侧影面积呈显著正相关关系,而植株疏透度与冠幅和侧影面积相关性不显著。

Application of Digitized Measurement in Upwind Projected Area of Desert Shrubs

Upwind projected area is a significant indicator of evaluating windbreak efficiency of plants,and how to get more accurate upwind projected area is an issue that needs to be addressed urgently when calculating roughness.In this study,the digital image method was used to calculate the values of upwind projected area of three desert plant species (Haloxylon ammodendron,Calligonum mongolicum and Reaumuria soongarica),the factors affecting the measurement were lucubrated,the merits and demerits of digital image method and other two methods were compared,and the correlations among upwind projected area,crown breadth and porosity were discussed to provide a reference for extracting information from desert shrubs and calculating roughness.The results showed that,compared with other two methods,the upwind projected area was closer to the true value because the area of numerous holes among branches and leaves did not be included in digital image method,though its operating process was relatively complicated and the stability of measured results was relatively poor.It was not significant that the area of reference substance and camera focal length affected the upwind projected area,but the position of reference substance,camera angle and tolerance were opposite in digital image method,and the measured result were obviously affected by background disturbance.There was a significantly positive correlation between upwind projected area and crown breadth of three desert plant species,but the porosity was not significantly correlated with crown breadth and upwind projected area.