用垂向光学辐照度测量数据计算雾能见度的方法和验证
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摘要
大气能见度是描述雾的重要物理参数。目前测量大气能见度是采用主动光源测量水平方向的可视距离,本文提出了用垂直方向测量的自然光光学数据计算能见度的方法,该方法通过测量两个不同高度上的谱辐照度,计算谱衰减系数,然后将自然光参数转换为标准光参数,按照大气能见度的定义计算能见度,形成了由垂向光学测量获取大气水平能见度的合乎规范的理论和实际可行的计算方法。在2016年5月5日,作者采用2台光学辐照度计(Trios)和1台能见度仪进行了9h的观测,获得了一个完整的雾生成和发展过程的观测数据,对本文提出的算法进行了检验。针对环境干扰因素可能导致虚报雾的情形,本项研究提出,先从光谱数据本身定性判断是否有雾,再通过本文提出的理论方法计算能见度。研究发现直射光和散射光在594和674nm的特异性,用归一化光谱之差作为判据,成为能见度是否小于2 000m的可靠判断方法。结果表明,光学观测的计算结果在能见度小于1 000m的均方根误差为173m,在能见度小于2 000m的均方根误差为471m。与通常使用的用550nm单一谱段衰减系数计算大气能见度的方法比较,精度有很大提高。尤其对于能见度小于2 000m的情形,与实测能见度有很高的一致性。用垂向光学辐照度观测结果计算能见度是可行的方法。
Atmosphere visibility is a key physical parameter to describe fog.Currently the atmospheric visibility is measured as a visible distance in horizontal direction by using an active emitted light source.In this paper,a new method is proposed to measure the visibility from optical irradiance of natural light in vertical direction.The measurement is conducted by two optical instruments at different altitudes to obtain spectral irradiances.The irradiance for nature light must be transformed to that of a reference light source(radiation of a filament lamp with color temperature of 2 700 K)to obtain the global attenuation coefficient(GAC)of reference light.Then the visibility is calculated with GAC as a new method to measure fog visibility from vertical irradiance data.This new method is in accords with the definition of visibility and operational in real measurement.The method is validated by the measurement data on 5 May 2016 for a whole fog process.Two optical instruments(TRIOS)are used for measuring the irradiance and an instrument for visibility(PWD22)for examination.As some factors could disturb the irradiance to give fault fog report,a criterion is proposed to judge fog situation based on the specificity of direct and scattering lights at594 and 674 nm wavelengths.The criterion could be used to judge if the visibility is less than 2 000 mprior to the visibility calculation.The r.m.s.deviation of retrieved fog visibility compared to the visibility measurement was 173 mfor fog visibility less than 1 000 and 471 mfor visibility less than 2 000 m.The retrieved results are accurate enough,especially in low visibility situation,which suggests that the method is applicable to retrieve fog visibility from vertical irradiance measurement.
Atmosphere visibility is a key physical parameter to describe fog.Currently the atmospheric visibility is measured as a visible distance in horizontal direction by using an active emitted light source.In this paper,a new method is proposed to measure the visibility from optical irradiance of natural light in vertical direction.The measurement is conducted by two optical instruments at different altitudes to obtain spectral irradiances.The irradiance for nature light must be transformed to that of a reference light source(radiation of a filament lamp with color temperature of 2 700 K)to obtain the global attenuation coefficient(GAC)of reference light.Then the visibility is calculated with GAC as a new method to measure fog visibility from vertical irradiance data.This new method is in accords with the definition of visibility and operational in real measurement.The method is validated by the measurement data on 5 May 2016 for a whole fog process.Two optical instruments(TRIOS)are used for measuring the irradiance and an instrument for visibility(PWD22)for examination.As some factors could disturb the irradiance to give fault fog report,a criterion is proposed to judge fog situation based on the specificity of direct and scattering lights at594 and 674 nm wavelengths.The criterion could be used to judge if the visibility is less than 2 000 mprior to the visibility calculation.The r.m.s.deviation of retrieved fog visibility compared to the visibility measurement was 173 mfor fog visibility less than 1 000 and 471 mfor visibility less than 2 000 m.The retrieved results are accurate enough,especially in low visibility situation,which suggests that the method is applicable to retrieve fog visibility from vertical irradiance measurement.
引文
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[21]耿彪,何永强,武琳,等.一种计算某一波段大气平均衰减系数的方法[J].红外技术,2009,31(6):323-326.Geng Biao,He Yongqiang,Wu Lin,et al.A method of calculating the coefficient of atmospheric average attenuation for certain spectral waveband[J].Infrared Technology,2009,31(6):323-326.
[22]黄成栋,李玮,刘瑞良,等.透射式能见度仪校准方法研究[J].气象水文海洋仪器,2018,35(1):17-19.Huang Chengdong,Li Wei,Liu Ruiliang,et al.Research on calibration methods of transmission visibility meter[J].Meteorological,Hydrological and Marine Instruments,2018,35(1):17-19.
[23]程守洙,江之永.普通物理学,第三册[M].北京:人民教育出版社,1998:314-327.Cheng Shouzhu,Jiang Zhiyong.General Physics,volume 3[M].Beijing:People's Education Press,1998:314-327.
[24]Zhang S,Yi L.A comprehensive dynamic threshold algorithm for daytime sea fog retrieval over the Chinese adjacent seas[J].Pure and Applied Geophysics,2013,170(11):1931-1944.
[2]李子华.中国近40年来雾的研究[J].气象学报,2001,59(5):616-624.Li Zihua.Studies of fog in China over the past 40Years[J].Acta Meteorological Sinica,2001,59(5):616-624.
[3]Gultepe I,Tardif R,Michaelides S C,et al.Fog research:A review of past achievements and future perspectives[J].Pure and Applied Geophysics,2007,164(6-7):1121-1159.
[4]Kumai M.Arctic fog droplet size distribution and its effect on light attenuation[J].Journal of the Atmospheric Sciences,1973,30(4):635-643.
[5]Chylek P.Extinction and liquid water content of fogs and clouds[J].Journal of the Atmospheric Sciences,1978,35(2):296-300.
[6]Sasakawa M,Uematsu M.Relative contribution of chemical composition to acidification of sea fog(stratus)over the northern North Pacific and its marginal seas[J].Atmospheric Environment,2005,39(7):1357-1362.
[7]Ogiwara S,Okita T.Electron-microscope study of cloud and fog nuclei[J].Tellus,1952,4(3):233-240.
[8]Rangognio J,Tulet P,Bergot T,et al.Influence of aerosols on the formation and development of radiation fog[J].Atmospheric Chemistry and Physics Discussions,2009(5):17963-18019.
[9]傅刚,李晓岚,魏娜.大气能见度研究[J].中国海洋大学学报(自然科学版),2009,39(5):855-862.Fu Gang,Li Xiaolan,Wei Na.Review on the atmospheric visibility research[J].Periodical of Ocean University of China:2009,39(5):855-862.
[10]Blackwell H R.Contrast thresholds of the human eye[J].JOSA,1946,36(11):624-643.
[11]Koschmieder H.Theorie der horizontalen Sichtweite[J].Beitrage zur Physik der freien Atmosphare,1924:33-53.
[12]林晔,王庆安,顾松山,等.大气探测学教程[M].北京:气象出版社,1993:79-98.Lin Ye,Wang Qingan,Gu Songshan,et al.Atmospheric Observation[M].Beijing:China Meteorological Press,1993:79-98.
[13]Hommersom A,Kratzer S,Laanen M,et al.Intercomparison in the field between the new WISP-3and other radiometers(TriOSRamses,ASD FieldSpec,and TACCS)[J].Journal of Applied Remote Sensing,2012,6(1):063615.
[14]Tveiter7)as J H.Characterization of Hyper Spectral Irradiance and Radiance Sensors[D].Bergen:The University of Bergen,2013.
[15]麦卡特尼.大气光学[M].北京:科学出版社,1988:45-46.Earl J.McCartney.Optics of the Atmosphere[M].Beijing:Science Press,1988:45-46.
[16]Jarraud M.Guide to Meteorological Instruments and Methods of Observation(WMO-No.8)[M].Geneva,Switzerland:World Meteorological Organisation:2008.
[17]盛裴轩,毛节泰,李建国,等.大气物理学[M].北京:北京大学出版社,2003.Sheng Peixuan,Mao jietai,Li Jianguo,et al.Atmospheric Physics[M],Beijing:Beijing University Press,2003.
[18]饶瑞中.现代大气光学[M].北京:科学出版社,2012.Rao Ruizhong.Modern Atmospheric Optics[M].Beijing:Science Press,2012.
[19]张纪伟,张苏平,吴晓京,等.基于MODIS的黄海海雾研究---海雾特征量反演[J].中国海洋大学学报(自然科学版),2009(s1):311-318.Zhang Jiwei,Zhang Suping,Wu Xiaojing,et al.The research on Yellow Sea Fog based on MODIS data:Sea fog properties retrieval and spatial-temporal distribution[J].Periodical of Ocean University of China,2009(s1):311-318.
[20]傅刚,徐杰,张树钦.数值模拟和卫星反演大气能见度对比分析[J].中国海洋大学学报(自然科学版),2011,41(4):1-10.Fu Gang,Xu Jie,Zhang Shuqin.Comparison of modeling atmospheric visibility with visible satellite imagery[J].Periodical of O-cean University of China,2011,41(4):1-10.
[21]耿彪,何永强,武琳,等.一种计算某一波段大气平均衰减系数的方法[J].红外技术,2009,31(6):323-326.Geng Biao,He Yongqiang,Wu Lin,et al.A method of calculating the coefficient of atmospheric average attenuation for certain spectral waveband[J].Infrared Technology,2009,31(6):323-326.
[22]黄成栋,李玮,刘瑞良,等.透射式能见度仪校准方法研究[J].气象水文海洋仪器,2018,35(1):17-19.Huang Chengdong,Li Wei,Liu Ruiliang,et al.Research on calibration methods of transmission visibility meter[J].Meteorological,Hydrological and Marine Instruments,2018,35(1):17-19.
[23]程守洙,江之永.普通物理学,第三册[M].北京:人民教育出版社,1998:314-327.Cheng Shouzhu,Jiang Zhiyong.General Physics,volume 3[M].Beijing:People's Education Press,1998:314-327.
[24]Zhang S,Yi L.A comprehensive dynamic threshold algorithm for daytime sea fog retrieval over the Chinese adjacent seas[J].Pure and Applied Geophysics,2013,170(11):1931-1944.