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Studying the vertical aerosol extinction coefficient by comparing in situ airborne data and elastic backscatter lidar

机译:通过比较原位机载数据和弹性反向散射激光雷达研究垂直气溶胶的消光系数

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摘要

Vertical profiles of aerosol particle optical properties were explored in acase study near the San Pietro Capofiume (SPC) ground station during thePEGASOS Po Valley campaign in the summer of 2012. A Zeppelin NT airship wasemployed to investigate the effect of the dynamics of the planetary boundarylayer at altitudes between ∼  50 and 800 m above ground. Determinedproperties included the aerosol particle size distribution, the hygroscopicgrowth factor, the effective index of refraction and the light absorptioncoefficient. The first three parameters were used to retrieve the lightscattering coefficient. Simultaneously, direct measurements of both thescattering and absorption coefficient were carried out at the SPC groundstation. Additionally, a single wavelength polarization diversity elasticlidar system provided estimates of aerosol extinction coefficients using theKlett method to accomplish the inversion of the signal, for a verticallyresolved comparison between in situ and remote-sensing results. Note,however, that the comparison was for the most part done in the altitude rangewhere the overlap function is incomplete and accordingly uncertainties arelarger. First, the airborne results at low altitudes were validated with theground measurements. Agreement within approximately ±25 and ±20 %was found for the dry scattering and absorption coefficient, respectively.The single scattering albedo, ranged between 0.83 and 0.95, indicating theimportance of the absorbing particles in the Po Valley region. A clearlayering of the atmosphere was observed during the beginning of the flight(until ∼  10:00 LT – local time) before the mixing layer (ML) was fullydeveloped. Highest extinction coefficients were found at low altitudes, inthe new ML, while values in the residual layer, which could be probed at thebeginning of the flight at elevated altitudes, were lower. At the end of theflight (after ∼  12:00 LT) the ML was fully developed, resulting inconstant extinction coefficients at all altitudes measured on the ZeppelinNT. Lidar estimates captured these dynamic features well and good agreementwas found for the extinction coefficients compared to the in situ results,using fixed lidar ratios (LR) between 30 and 70 sr for the altitudes probedwith the Zeppelin. These LR are consistent with values for continentalaerosol particles that can be expected in this region.
机译:在2012年夏季的PEGASOS Po Valley战役期间,在圣彼得罗·卡波菲姆(SPC)地面站附近进行了一项案例研究,探索了气溶胶粒子光学特性的垂直剖面。雇用Zeppelin NT飞艇调查了行星边界层动力学在海拔约50至800 m。确定的性能包括气溶胶粒径分布,吸湿性增长因子,有效折射率和光吸收系数。前三个参数用于检索光散射系数。同时,在SPC地面站直接测量了散射系数和吸收系数。此外,一个单波长偏振分集弹性激光系统使用Klett方法提供了气溶胶消光系数的估计值,以完成信号的反演,从而实现了原位和遥感结果之间的垂直分辨比较。但是请注意,比较大部分是在重叠函数不完整且不确定性较大的海拔范围内完成的。首先,低空飞行结果已通过地面测量得到验证。干散射系数和吸收系数分别在约±25%和±20%范围内一致。单个散射反照率在0.83至0.95之间,表明波谷地区吸收粒子的重要性。在飞行开始之前(直到当地时间〜10:00 LT),在混合层(ML)完全展开之前,观察到了一个清晰的大气层。在新的ML中,在低海拔处发现了最高的消光系数,而在海拔较高的飞行开始时可以探测到的残留层中的值较低。飞行结束时(约LT 12:00之后),ML完全发育,因此在ZeppelinNT上测得的所有高度上的消光系数都恒定。激光雷达的估计很好地捕获了这些动态特征,并且与原位结果相比,对于灭绝系数而言,使用齐柏林飞艇探测到的高度使用了固定的激光雷达比率(LR)在30至70LRsr之间时,发现了很好的一致性。这些LR与在该区域可以预期的大陆气溶胶颗粒值一致。

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