【作者】 周文君；

【导师】 牛生杰；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2012， 硕士

【摘要】 全天空成像仪(Total Sky Imager,TSI-440)可以实现白天全天空云量的持续自动监测,时空分辨率高。为了进一步提高TSI-440仪器的观测准确度,本文首先介绍了TSI-440的基本原理和资料格式,进而基于太湖自动观测站2008年5月-2009年4月的TSI资料及无锡站地面观测资料,采用统计分析和直方图分析法建立了本地化阈值选择方案,改进了云量计算方法,主要得到以下结论：1、图像的成像特征与能见度密切相关,像元点的红蓝比值随着能见度的减小而增大。2、晴空及少云时,气溶胶前向散射易造成10%-20%的云量计算误差。针对这种情况,本文基于Long方案改进了云量计算方案,通过与目测结果对比表明：新方案有效减小了晴空、少云时太阳圈及近地平区域云量计算误差。3、针对阴天图像及复杂天空(多云)图像,本文基于直方图分析法,重新计算了红蓝比阈值(晴空点阈值0.62；云点阈值0.66),对比结果表明：基于新阈值计算的云量较仪器自带处理结果绝对误差减小13.75%。总体来说,改进方案计算的云量较TSI原始结果平均绝对误差减小9.06%,证明了新方案的有效性。更多还原

【Abstract】 The Total Sky Imager (TSI-440) is designed to automatically monitor cloud conditions at daytime with higher spatial resolutions, providing much more accurate cloud cover data in real time. The paper analyzed the image data and the routine surface observation of the automatically observation site in TaiHu from May,2008to Apirl,2009, using the method of statistics and histogram analysis to improve the method of cloud cover calculations. We can get following conclusions:1. Imaging characteristic is closely bound up with the visibilities; the red blue ratio will increase along with the reducing visibilities.2. Through the visual recognition, we find that the TSI has certain errors (about10%to20%) on sunny days. This paper used the improved method of sky cover calculation and found that the method decreased the calculation errors effectively.3. It also finds that the TSI-440has certain errors in processing cloudy day images. The paper analyses the RGB characteristic and set new thresholds (sunny points0.62; cloudy points0.66) and count the cloud points. The recalculated results are much more accurate than the raw results from the TSI. The absolute error has been decreased for13.75%.In conclusion, the new methods could reduce the cloud cover errors for9.06%. It has proved the validity of the improved method in this paper.更多还原