为研究低分辨率气象卫星数据云检测的尺度误差及其给下行辐射计算带来的影响,利用高分辨率静止卫星GF-4数据进行云检测并进行误差分析。首先运用可见光通道阈值法和时间序列法,对GF-4数据进行云检测,以GF-4云检测结果为基准,分析Himawari-8和FY-2(FY-2G和FY-2E)云检测结果的误差。在研究区内FY-2G,FY-2E与Himawari-8云图能够将云和晴空较好的区分开,造成误差的主要原因是不同空间分辨率卫星所产生的尺度效应(云检测算法不同造成的差异在此不予讨论),误差大多发生在薄云以及碎云较多的区域,高分辨率数据能够较好地检测出碎云,而低分辨率数据则会产生误检、检等情况。在此基础上对下行短波辐射遥感计算的误差进行分析,发现像元中实际云量的误差会给下行辐射的估算带来明显误差,所选试验区瞬时下行辐射相对误差最大为-173.52%,日总下行短波辐射相对误差最大为-20.20%。研究结果表明,在碎云较多的区域,利用高分辨率静止卫星数据可以显著提高下行短波辐射的估算精度。

In order to study the scale error of low resolution meteorological satellite cloud detection and its impact on the calculation of downlink radiation, cloud detection using high resolution stationary satellite GF-4 data and error analysis were carried out. Firstly, the cloud detection of GF-4 data is carried out by using visible channel threshold method and time series method, and the error of cloud detection results of Himawari-8 and FY-2 (FY-2G, FY-2E) is analyzed based on the results of GF-4 cloud detection.In the study area, FY-2G, FY-2E and Himawari-8 cloud images could distinguish the clouds and clear sky. The main reason for the error was the scale effect produced by different spatial resolution satellites(the differences caused by cloud detection algorithms are not discussed here).Most of the errors occurred in the areas of thin clouds and broken clouds.High resolution data could detect broken clouds, while low resolution data lead to false and missed detection. On this basis, the error of remote sensing calculation of short wave radiation was analyzed,and it was found that the error of the actual cloud amount in the pixel would bring significant error to the estimation of the downward radiation.The relative error of the instantaneous downward radiation in the selected test area was -173.52%, and the maximum relative error of shortwave radiation was -20.20%.The results show that the high resolution stationary satellite data can significantly improve the estimation accuracy of the downlink shortwave radiation in the regions with more broken clouds.