云的移动轨迹成像模拟及云量变化分析

Track-Simulation of Cloud's Motion and the Analysis of Variations of Cloud-Fraction

摘要:

以全天空数字成像仪的等角投影成像原理为基础,将云型简化为正方体及圆柱体云体,模拟了相同云体在不同空间位置的移动轨迹情况,对其所占面积变化(云量)进行了计算,并对云在移动过程中云体侧面成像情况做了分析研究。结果表明,云量随空间位置变化情况与云的宽高比相关,当宽高比大于某一值时云量随天顶角(云所处位置)的增大先增大而后减小,反之则随着天顶角的增大而减小。

关键词:云量;全天空;轨迹;等角投影

Abstract:

A same cloud has different view-angles when it moves from overhead toward the near-horizon.In this paper,we simulate the track of the cloud's movement based on the principle of the equi-angle projection of all-sky imager(fish-eye lens) and estimate the cloud fraction during its movement.The cloud is simplified as the cubic and cylindric objects of two different sizes in the simulation.To get the characteristics of variations of the cloud fraction,we calculate the cloud amount and the ratio of the cloud's frank-fraction to the cloud-fraction during the movement of the cloud.Results show that the variation of the cloud-fraction is related to the ratio of the cloud's base to height(RBTH).When the RBTH is larger than a threshold,the cloud-fraction will increase at first and then decrease with the zenith angle's increase.Otherwise,it will decrease all the time.The degree of the decrease is related to some parameters such as the height,RBTH and size of the cloud.And the frank-fraction will account for more and more portion of the whole cloud cover when the zenith angle increases.

Key words:cloud fraction;all-sky;track;equi-angle