A new method for retrieving cloud optical depth (COD) using AERONET cloud mode is introduced. Using statistical analysis for temporal variation characteristics of cloud optical properties at Xianghe site based on the COD data obtained by this algorithm from January 2011 to June 2012, we find that there was significant daily variation COD in zenith direction and the number of occurrence of non-precipitating clouds (Num). Comparing the COD data retrieved by ground-based remote sensing and MODIS satellite under different sky conditions (broken clouds and overcast cases), the two data sets fit very well with high correlation. In these two cases, the average values of MODIS COD are 10.8 and 9.4, smaller than those of ground observation. COD had a decreasing trend in the morning and dusk, and a increasing trend at noon and in the afternoon. Num day curve was "bimodal" and peaked in the morning and afternoon, respectively, with a minimum around noon. The seasonal average COD was in the order of autumn>spring> winter> summer, each season had more than 65% of the COD concentrated in the range of 10~40; summer observations showed the maximum number of days, minimum change. At least a few days in the winter observations, it showed the maximum change. The observed days or change were consistent in spring and autumn. A linear regression analysis for COD and AOD time series was used at Xianghe site, and a significance test was carried out, showing that observed frequency of COD and fine mode AOD had a strong positive correlation.%基于地基天顶角辐射测量方法的AERONET云模式可反演云光学厚度(COD),结合MODIS卫星反演的云产品资料,对2011年1月~2012年6月香河站云光学特性进行分析,并讨论了气溶胶光学厚度(AOD)和COD间的关系.结果表明:碎云和阴天状况下,地基和卫星资料反演云的COD存在显著的正相关,MODIS反演的COD平均值比地基观测值分别小10.8和9.4;香河站天顶角方向COD和非降水云出现次数(Num)存在显著的日变化:COD在早晨和黄昏有减小趋势,在中午和下午有增大趋势;Num日变化曲线呈双峰型,峰值分别出现在早晨和午后,最小值出现在正午前后;COD季平均值为秋>春>冬>夏,各季都有超过65%的COD集中在10~40;夏季观测天数最多,变化程度最小;对香河站COD与AOD时间序列作线性回归分析,并进行显著性检验,发现COD的观测频率和细模态AOD有较强的正相关性.
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