利用全天空可见光图像反演天空辐亮度

A method to retrieve the radiance from all-sky visible images.

中文关键词:  全天空, 可见光成像, 图像, 辐亮度, 云

英文关键词:All-sky, Visible imaging, Image, Radiance, Cloud

中文摘要:

      由中国科学院大气物理研究所LAGEO实验室研制和开发的地基全天空成像仪,可实现地基全天空自动化观测，文中首先对全天空成像仪仪器及性能进行介绍。辐亮度是气象科学研究中基础而重要的气象要素，而全天空成像仪记录的是可见光红、绿、蓝三波段辐射信息的灰度值图像，因而无法直接应用到气象研究中。为能够从灰度值图像中获取天空辐亮度信息，文中详细介绍了与亮度反演密切相关的几个重要标定实验，包括几何标定、光学标定，以标定参数为基础并结合全天空仪器成像原理提出了一个由可见光灰度图像反演相对天空辐亮度分布的算式算法。文中还利用大气物理研究所香河观测站 （39.75°N, 116.96°E）同时观测的全天空成像仪以及CIMEL光度计所观测的天空辐亮度数据(440 nm波长)，对该反演算式进行检验和比对，结果表明，所提出的算法进行天空辐亮度分布反演可行，该算法将灰度图像与天空辐亮度建立了联系，有利于观测图像数据与数值模式模拟工作的相互对比和验证，有利于观测图像数据在模式研究中的应用。

英文摘要:

      The automatic ground based all sky imager developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences is able to obtain visible gray images of the sky radiance in red, green and blue channels. The paper introduces this all sky imager system and its capabilities. Radiance, a key parameter for meteorological researches, is recorded as gray value by the all sky imager and can not be used directly for meteorological study. In order to extract the radiance from all sky images, this paper shows some necessary calibration experiments on the imager system. On the basis of the calibration results and the projection principles of the all sky imager, an algorithm to retrieve the relative radiance from the all sky images is then presented. Then using the images obtained from the all sky imager and the radiance at 440 nm wavelength from the CIMEL instrument at Xianghe Observatory in Hebei province （39.75°N，116.96°E）, we make a intercomparison between the retrieval radiance and the measured one. The comparison results show that the retrieval algorithm is feasible. This work sets up a relationship between the radiance and the image data and it is useful for the image data to be made comparison with the numerical simulation results and to be applied into numerical model simulation studies.