全天空成像仪TSI-440云量计算方法的改进
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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。
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.
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。
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.
引文
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[30]何荥,翁季,等.用鱼眼镜头数码相机测试天空亮度分布[J].重庆大学学报,2010.33(7)：129-134.
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[37]MorrisVR. Total Sky Imager hand book [EB/OL]. J. Tech. Rep. ARM TR-017, 2005.Available via http://www.arm.gov/.
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[39]Hodges G. A Comparison of fractional cloud cover determination by a sky image with visual estimation by trained national weather service observers [EB/OL].1998. Available via http://www.noaa.gov/.
[40]Pfister G, McKenzie R L. Cloud coverage based on all-sky imaging and its impact on surface solar irradiance [J].2003.Amer. Meteor. Soc.42:1421-1434.
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[45]霍娟,吕达仁.利用全天空数字图像对北京上空云况分布特征的实验分析[J].气象科学,2005.25(3)：238-243.
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[1]Long C N. Total Sky Imager installation and user guide [EB/OL], YANKEE Environmental System, Inc.,2001, Available via http://www.yesinc.com/.
[2]Long C N, Slater D W, and Tooman T. Total Sky Imager (TSI) Model 880 status and testing results. Atmospheric Radiation Measurement Program Tech. Rep. ARM TR-004,2001.
[3]盛裴轩,毛节泰,等.大气物理学[M],北京大学出版社.2003.
[4]Morris V R. Total Sky Imager handbook [EB/OL]. J. Tech. Rep. ARM TR-017,2005, Available via http://www.arm.gov/.
[5]Long C N, Sabburg J M. Retrieving cloud characteristics from ground-based daytime color all-sky images [J]. J. Atmos. Oceanic Tech.,2006,23(5):633-652.
[6]詹青龙,卢爱芹,等.数字图像处理技术[M],清华大学出版社.2010.
[1]Long C N, Slater D W, and Tooman T.2001.Total Sky Imager (TSI) Model 880 status and testing results. Atmospheric Radiation Measurement Program Tech. Rep. ARM TR-004.
[2]Pfister G, McKenzie R L. Cloud coverage based on all-sky imaging and its impact on surface solar irradiance [J].2003.Amer. Meteor. Soc.42:1421-1434.
[3]Sabburg J M, Long C N.2004.Improved sky imaging for studies of enhanced UV irradiance[J]. Atmos. Chem. Phys.4:2543-2552.
[4]Long C N.2010.Correcting for circumsolar and near-horizon errors in sky cover retrievals from sky images [J]. J. Atmos. Soc.4(1):45-52.
[5]Kassianov E, Long C N.2005. Cloud sky cover versus cloud fraction:whole-sky simulation and observations. J. Appl. Meteor.,44:86-98.
[1]束家鑫,鲍宝堂,中国云天[M].上海科学普及出版社.1994.
[2]何荥,翁季,等.用鱼眼镜头数码相机测试天空亮度分布[J].重庆大学学报,2010.33(7)：129-134.
[3]Long C N, Sabburg J M. Retrieving cloud characteristics from ground-based daytime color all-sky images[J]. J. Atmos. Oceanic Tech.,2006.23(5):633-652.
[2]黄美元,等.云和降水物理学,科学出版社,1999.
[3]盛裴轩,毛节泰,等.大气物理学[M],北京大学出版社.2003.
[4]陈洪滨.关于云和云天大气对太阳辐射的吸收异常[J].大气科学,1997,21(6)：750-757.
[5]Calbo J, Pages D.Empirical studies of cloud effects on UV radiation:A Review [J]. J. Geophys.2002. Res.43(2):1-28.
[6]Long CN,Thoman P. Identification of clear skies from broadband dynamometer measurements and calculation of down-welling shortwave cloud effects [J]. J. Geophys. Res.2000.105(12):15609-15626.
[7]Long CN.The shortwave clear-sky detection and fitting algorithm:algorithm operational details and explanations. Atmospheric Radiation Measurement Program Tech.2004. Rep. ARM TR-004.
[8]气象仪器和观测方法指南,气象出版社,1995.
[9]张霭琛.现代气象观测[M],北京大学出版社.2000.
[10]张春光,张域钧.测云技术研究进展[J].光散射学报.2007.19(4)：388-394.
[11]翁笃呜,韩爱梅.我国卫星总云量与地面总云量分布的对比分析.应用气象学报,1998,9(1)：32237.
[12]张培昌,戴铁不等编著,雷达气象学[M],北京,气象出版社,1998.
[13]吕仁达,王普才,等.大气遥感与卫星气象学研究的进展与回顾.大气科学,2003,27(4)：552-565.
[14]陈渭民,边多,郁凡.由卫星资料估算晴空太阳直接辐射和散射辐射[J].南京气象学院学报.1997.20(3)：326-333.
[15]宋庆利.利用卫星资料研究云对地面净辐射的影响[D].南京气象学院硕士学位论文.2003.
[16]Martins F R, Souza M P, and Pereira E B. Comparative study of satellite and ground techniques for cloud cover determination [J].2003.Space Res.32(11):2275-2280.
[17]束家鑫,鲍宝堂,中国云天[M].上海科学普及出版社.1994.
[18]Bradbury D L, Fujita T. Computation of Height and Velocity of Clouds from Whole-sky Time-lapse Picture Sequences. Satellite and Micrometeorology Research Project6 (SMRP), 1968.
[19]K.McGuffie, A.Henderson-sellerst, Almost a Century of "Imaging" Clouds Over the Whole Sky Dome, Bulletin American Metrological Society, Vol.70, No.10,1989,1243-1989.
[20]霍娟.全天空数字相机观测云量的初步研究[D].南京气象学院硕士学位论文.2002.
[21]霍娟,吕仁达.地基全天空成像系统云与气溶反演及其应用研究[D].中国科学研究院博士学位论文.2007.
[22]Steven A, Ackerman and Stephen K. Cox, Comparison of Satellite and All-Sky Camera Estimates of Cloud Cover during GATE, Journal of Applied Meteorology, Vol.20,No.5,1981,581-587.
[23]Gardiner B G, Kirsch P J. Setting Standards for European Ultraviolet Spectroradiometers. EC Air Pollution Report No.53, Commission of European Communities Luxembourg,1995:138.
[24]Giuseppe Zibordi. Radiometric and Geometric Calibration of a Visible Spectral Electro-Optic"Fisheye"Camera Radiance Distribution System. American Meteorological Society,1989(6):652-662.
[25]孙学金,刘磊,高太长,等.基于模糊纹理光谱的全天空红外图像云分类[J].应用气象学报,2009.20(2)：157-163.
[26]高太长,刘磊,赵世军,等.全天空测云技术现状及发展[J].应用气象学报,2010.21(1)：100-109.
[27]Morris V R. Whole Sky Imager hand book [EB/OL]. J. Tech. Rep. ARM TR-017, 2001.Available via http://www.arm.gov/.
[28]Li Z,Cribb M C,Chang F L.Validation of MODIS-Retrieved Cloud Fractions Using Whole-Sky Imager Measurements at the Three ARM Sites. Fourteen ARM Science Team Meeting Proceedings, March 22-26,2004.
[29]霍娟,吕仁达,等.全天空数字相机观测云量的初步研究[J].南京气象学院学报.2002.Vol.25 NO.2：242-246.
[30]何荥,翁季,等.用鱼眼镜头数码相机测试天空亮度分布[J].重庆大学学报,2010.33(7)：129-134.
[31]孙学金,高太长,翟东力,等.基于非制冷红外焦平面阵列的全天空红外测云系统.红外与激光工程,2008,37(5)：761-764.
[32]Cazorla A, Olmo F J, Alados Arboledas L. Development of a sky imager for cloud cover assessment. J.Opt. Soc.A mA,2008,25 (1):29239.
[33]Shaw J A, Thurairajah B, Edqvist E, et al. Infrared Cloud Imager Deployment at the North Slope of Alaska During Early 2002.12th ARM Science Team Meeting, Washington DC,2002.
[34]Long C N, Deluisi J J. Development of an automated Hemispheric Sky Imager for cloud fraction retrievals [C]. Proc.10th symposium on Meteorological Observations and Instrumentation. Phoenix, Arizona, Amer. Meteor. Soc:1998.171-174.
[35]Smith S, Toumi R. Measuring cloud cover and brightness temperature with a ground-based thermal infrared camera. J.A ppl. Meteorol. Climate,2008,47 (2):6832693.
[36]Long C N. Accounting for circumsolar and horizon cloud determination errors in sky image infernal of sky cover. Proc.l5th Atmospheric Radiation Measurement Science Team Meeting,2005.Daytona Beach, FL, Department of Energy ARM Program.
[37]MorrisVR. Total Sky Imager hand book [EB/OL]. J. Tech. Rep. ARM TR-017, 2005.Available via http://www.arm.gov/.
[38]Long C N, Slater D W, and Tooman T. Total Sky Imager (TSI) Model 880 status and testing results. Atmospheric Radiation Measurement Program Tech. Rep. ARM TR-004.2001.
[39]Hodges G. A Comparison of fractional cloud cover determination by a sky image with visual estimation by trained national weather service observers [EB/OL].1998. Available via http://www.noaa.gov/.
[40]Pfister G, McKenzie R L. Cloud coverage based on all-sky imaging and its impact on surface solar irradiance [J].2003.Amer. Meteor. Soc.42:1421-1434.
[41]Sabburg J M, Long C N. Improved sky imaging for studies of enhanced UV irradiance[J]. 2004.Atmos. Chem. Phys.4:2543-2552.
[42]Pages D, Calbo J, and Long C N. Comparison of several ground-based cloud detection techniques. Extended Abstracts, European Geophysical Society ⅩⅩⅦ General Assembly, Nice, France, European Geophysical Society, CD-ROM.2002.
[43]Lu D, Huo J. All-sky visible and infrared images for cloud macro characteristics observation [C]. Proc.14th int. Conf. on Cloud and Precipitations,2004, Vol.2, Bologna, Italy, ICCP, IAMAS,1127-1129.
[44]Kassianov E, Long C N. Cloud sky cover versus cloud fraction:whole-sky simulation and observations. J. Appl. Meteor.,2005.44:86-98.
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