数值模拟显示在太阳光前向散射角5°范围内, 视场变化探测的信号对卷云的光学厚度和有效尺度敏感。研发了一种基于图像跟踪的自动快速变视场太阳光度计(VFOVSP), 可快速测量不同视场太阳的直接辐射, 为地基测量卷云提供了一种新的技术手段。该仪器采用图像跟踪技术, 解决了薄云条件下四象限跟踪失效的问题。采用程控可变视场光阑, 该仪器实现了短时间内不同视场的快速测量。将该仪器测量的气溶胶光学厚度(AOT)与太阳光度计(POMO2型)的测量结果进行了对比, 结果显示该仪器测量的AOT方均根误差小于0.5%, 这表明该仪器测量气溶胶的精度高。结合不同的天气条件, 分析了该仪器不同视场比值的变化, 比值的变化与粒子尺度和光学厚度有关, 为反演卷云的光学特性提供了可能。

The numerical simulation shows that the signal of field change detection is sensitive to the optical thickness and effective scale of the cloud in the range of 5° of the forward scattering angle of the sun. We develop a solar photometer (VFOVSP) based on image tracking and automatic fast changing field of view. It can quickly measure the direct radiation of different fields of view and provide a new technical mean for ground measurement of cirrus. The instrument makes use of image tracking technology to solve the problem of four quadrant tracking failure under the condition of thin cloud. A programmable variable field aperture is used to measure the different fields of view in a short time. The aerosol optical thickness (AOT) measured by VFOVSP is compared with that by a solar photometer (POMO2). The root mean square error of the AOT measured by VFOVSP is less than 0.5%, which indicates that the instrument has a high accuracy in the aerosol measurement. The change of the field ratio is analyzed under the different weather conditions. The change of the ratio is related to the particle size and the optical thickness, which provides possibility for retrieving optical properties of cirrus clouds.