用于偏振云粒子探测系统的典型非球形粒子散射特性模拟
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摘要
为进一步了解云物理过程,探测冰云及混合相云云粒子特性,提出了一种带有偏振通道的云粒子探测器模型,可以同时探测前向散射和后向散射一定立体角内的散射能量和退偏比。模拟了椭球,圆柱和球形粒子的相函数,不同角度的退偏比,总散射截面,发现球形粒子几乎不产生退偏,其退偏与椭球、圆柱粒子退偏有数个量级的差距,探测时可以直接以退偏分辨球形粒子。计算了在探测器前后两个接收立体角内非球形粒子的散射截面和退偏比均值,粒子退偏比和散射截面随粒子的横纵比变化比较连续,一定条件下可以分辨部分粒子的形状。粒子退偏比随粒子的等效半径变化波动,不利于探测时分辨粒子大小。在模拟的粒径范围内,粒子等效半径和散射截面大致成正相关,探测时可以以此分辨粒子大小。粒子散射模拟结果表明,该探测系统除可以进行球形粒子探测能力外,具有一定的非球形粒子探测能力。
In order to detect characteristics of ice cloud and mixed phase cloud and further understand the process of cloud physics,a cloud particle detector with polarization channel which can simultaneously detect the depolarization ratio of backscattering and the scattering energies of forward scattering is presented in a fixed solid angle.The phase function,depolarization ratio of different angles,total scattering cross section of the ellipsoid,cylindrical and spherical particles has been simulated.We found that spherical particles have almost no depolarization,and the depolarization ratios of ellipsoid,cylindrical particles are several magnitude larger,so the spherical particles can be distinguished from nonspherical particles by depolarization ratios.The mean depolarization ratio and particle scattering cross section of nonspherical particle at the two receiving solid angles has been caculated,depolarization ratio and particle scattering cross section varies with aspect ratio smoothly,which makes the distinguish-ment between particles with different aspect ratio more directly.Particle depolarization ratio changes with the equivalent radius of the particle fluctuately,which goes against the detection.The equivalent particle radii and the scattering cross section are generally in positive correlation,so the particle size can be detected by their scattering cross sections.The simulation results shows that the detection system has the ability to detect nonspherical particles in addition to the ability for spherical particles detection.
In order to detect characteristics of ice cloud and mixed phase cloud and further understand the process of cloud physics,a cloud particle detector with polarization channel which can simultaneously detect the depolarization ratio of backscattering and the scattering energies of forward scattering is presented in a fixed solid angle.The phase function,depolarization ratio of different angles,total scattering cross section of the ellipsoid,cylindrical and spherical particles has been simulated.We found that spherical particles have almost no depolarization,and the depolarization ratios of ellipsoid,cylindrical particles are several magnitude larger,so the spherical particles can be distinguished from nonspherical particles by depolarization ratios.The mean depolarization ratio and particle scattering cross section of nonspherical particle at the two receiving solid angles has been caculated,depolarization ratio and particle scattering cross section varies with aspect ratio smoothly,which makes the distinguish-ment between particles with different aspect ratio more directly.Particle depolarization ratio changes with the equivalent radius of the particle fluctuately,which goes against the detection.The equivalent particle radii and the scattering cross section are generally in positive correlation,so the particle size can be detected by their scattering cross sections.The simulation results shows that the detection system has the ability to detect nonspherical particles in addition to the ability for spherical particles detection.
引文
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[3]李娟,毛节泰.大气冰核浓度对冷云辐射特性的影响以及多年来冷云反照率的变化[J].科学通报,2005,50(21):2413-2421.(LI Juan,MAO Jietai.The influence of atmospheric ice core concentration on the radiative properties of cold clouds and the changes of cold cloud albedo over the years[J].Chinese Science Bulletin,2005,50(21):2413-2421.)
[4]MANFRED W,LOUIS J,BRENGUIER.Airborne measurements for environmental research:methods and instruments[M].John Wiley&Sons,2013
[5]BAUMGARDNER D,BRENGUIER J L,BUCHOLTZ A,et al.Airborne instruments to measure atmospheric aerosol particles,clouds and radiation:A cook's tour of mature and emgerging technology[J].Atmos Res,2011,102(1-2):10-29.
[6]BAUMGARDNER D,JONSSON H,DAWSON W,et al.The cloud,aerosol and precipitation spectrometer:a new instrument for cloud investigations[J].Atmos Res,2001,59-60:251-264.
[7]LAWSON R P,BAKER B A,SCHMITT C G,et al.An overview of microphysical properties of arctic clouds observed in May and July 1998during FIRE ACE[J].J Geophys Res:Atmos(1984-2012),2001,106(D14):14989-15014.
[8]LAWSON R P,BRAD B,BRYAN P,et al.In situ observations of the microphysical properties of wave,cirrus,and anvil clouds.Part II:Cirrus clouds[J].J Atmos Sci,2006,63(12):3186-3203.
[9]JACOB P F,RAYMOND A S,EWE W S,et al.Airborne digital holographic system for cloud particle measurements[J].Appl Opt,2004,43(32):5987-5995.
[10]FUGAL J P,SHAW R A.Cloud particle size distributions measured with an airborne digital in-line holographic instrument[J].Atmos Meas Tech,2009,2(1):259-271.
[11]HIRST E,KAYE P H,GREENAWAY R S,et al.Discrimination of micrometre-sized ice and supercooled droplets in mixed-phase cloud[J].Atmos Environ,2001,35(1):33-47.
[12]RICHARD C,OSBORNE S,ULANOWSKI Z,et al.The ability of the Small Ice Detector(SID-2)to characterize cloud particle and aerosol morphologies obtained during flights of the FAAM BAe-146research aircraft[J].J Atmos Ocean Tech,2010,27(2):290-303.
[13]ULANOWSKI Z,KAYE P H,HIRST E,et al.Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements[J].Atmos Chem Phys,2014,14(3):1649-1662.
[14]许丽生,陈洪滨,丁继烈,等.非球形粒子光散射计算研究的进展综述[J].地球科学进展,2014,(08):903-912.(XU Lisheng,CHEN Hongbin,DING Jilie,et al.An overview of the advances in computational studies on light scattering by nonspherical particles[J].Advances in Earth Science,2014,29(8):903-912.)
[15]MISHCHENKO I M,TRAVIS L D.Capabilities and limitations of a current fortran implementation of the T-Matrix method for randomly oriented,rotationally symmetric scatterers[J].J Quant Spectrosc Ra,1998,60(3):309-324.