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激光雷达光谱仪(lissi)

一个完全新仪器的安装,目前正在设计在我们的实验室。与ZEMAX模拟Tm值 give us important information such as what strengths we can expect from our 拉曼散射 and fluorescence signals at various excitation wavelengths. The software allows investigating the correct positioning of the lasers, the optics, and detectors in order to maximize the signal strengths required to turn the laser spectroscopy instrument into a lidar instrument. Among the various parameters critical to a lidar is the temporal resolution of the measurements. This property determines the vertical resolution of the profiles of atmospheric pollution we are interested in as well as the integration time required for analysing the measurements.

A sketch of the lissi facility is presented below. The main components are one high power Nd:YAG laser (green), one optical parametric oscillator (OPO) (light green), beam expanders (blue), aerosol chambers for gases, liquids, and particles (grey), an array of spectrometers (yellow), the signal detection unit (red), a telescope for near and far range signal detection in the atmosphere (yellow), and a Raman microscope (black). The arrows indicate possible paths of the laser-light beams and the signals, which depends on the exact configuration of the final system design. Dots indicate optical elements that are used to direct the signals to the spectrometers and the detector unit.

仪器 LiSsl

这种激光装置将补充我们的专业知识方面的气溶胶污染的光学特性测量的基础上, 拉曼散射。我们也有20个年的专业经验中发展 反演算法,最近我们开始在数据挖掘工作, 人工神经网络(ANN)。这些工具被用于导出微粒污染,即微物理性质,平均粒子大小,数量,表面面积和体积浓度从与多波长拉曼激光雷达和多波长HSRL(高光谱分辨率激光雷达)的测量并且该组合多波长激光雷达无源远程传感器诸如日照计。在这方面AERONET太阳光度计是我们的光学数据的主要来源。我们在操作这些仪器之一我们 bayfordbury天文台 位于北哈特菲尔德。

lissi项目的概念验证

The lidar facility will be developed on the basis of experience we gain with our mrs.lea lidar instrument that is operated in South Korea. This lidar has been used since 2010 to measure one main component of mineral dust, i.e. silicon dioxide in mineral dust. Silicon dioxide is the most abundant chemical component of mineral dust; roughly 30% – 75% of East Asian dust consists of silicon dioxide (mineral quartz). Our lidar in South Korea until now has provided us with a wealth of data on East Asian dust plumes. The following section provides a few more details of the work we are carrying out in Korea on the basis of two measurement examples.

石英测量(二氧化硅)东亚混合污染羽状

我们开发了一种利用由二氧化硅拉曼散射的信号的新的测量通道(SIO2) quartz at ultraviolet wavelengths. The quartz is excited with the primary wavelength of 355 nm which subsequently leads to the emission of photons at 361 nm. In combination with Raman signals from scattering from nitrogen molecules we infer the mineral-quartz-related backscatter coefficient. This technique thus allows us to identify in a comparably direct way the mineral quartz content in mixed pollution plumes that consist, e.g., of a mix of desert dust and urban pollution. The technique is built upon experience gained in previous work [tatarov等人,2005年其中使用]在532nm的激发波长。

方法

该方法的基本思想是使用石英作为用于检测矿尘示踪剂。为了这个目的,我们测量来自石英颗粒从拉曼散射信号[Muller等人,2010; tatarov等人,2011]。拉曼反向散射系数βR(R,λL,λR)散射体可以从所接收到的拉曼散射信号来确定。二氧化硅的在大气中的质量浓度可以从石英的拉曼反向散射系数来估计。我们使用拉曼反向散射系数与拉曼散射微分截面Dσ连接关系(λL,λR,π)/Dω和石英分子数密度nq。该关系被限定为:

Raman quartz equation

使用这个公式,我们可以估算数密度nq 如果差分截面是已知的。我们乘以Ñ获得矿物石英的质量浓度q 用二氧化硅的分子质量。

mrs.lea的仪器设置用于拉曼测量的石英

mrs.lea detector

上图为mrs.lea的设置,当它被用于二氧化硅的拉曼散射测量。在361纳米的拉曼信号(主发光波长为355纳米),并在546nm处(主发光波长为532nm)进行测定。分束器用于将各种信号分离。在光电倍增管的前端干涉滤光器,然后用于测量在期望的波长处的背散射光子。

测定例:2010年3月 - 与mrs.lea第一观察

下面的示例示出了与我们的拉曼硅二氧化物拉曼频道[的优化建立进行混合粉尘/工业污染羽流的第一观察Muller等人,2010; tatarov等人,2011; 2012 500 Internal Server Error

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Time-height cross section on 21 March 2010

的确,无机尘埃的量化和的这种灰尘与工业污染的混合状态是困难的进行没有它可以用作无机灰尘直接示踪剂二氧化硅的拉曼信号的附加知识。我们的数据的进一步分析揭示了该混合粉尘/污染羽流的纯矿物粉尘含量的轮廓。

Single profiles

上面的图示出了第一组的SiO2 - 相关拉曼反向散射曲线曾经在355纳米激光的激发波长测量的。我们还在355nm和用于质量保证目的532纳米进行矿物石英的第一时间同步测量。在这方面, tatarov等。 [2005] 的矿尘显示简档中的532nm的激发波长测量的。

Mass profiles

The figure above shows the comparison of the quartz profiles measured at 361 and 546 nm. From a theoretical point of view both profiles should be on the same as there is no physical reason why the dust concentration should depend on the measurement wavelength. Accordingly, the Ångström exponent should be 4, corresponding to molecular scattering by the silicon-dioxide molecules. We find a value close to 4 but not exactly 4. There may be various reasons for the observed deviation like measurement uncertainties, a wrong calibration of the instrument or measurements channels, misalignment of the measurement channels, etc. Details of this measurement case are described by tatarov等。 [2011].

最强东亚灰尘发生在过去70年的韩国

前面的例子显示,在2010年3月21日当天的测量情况之前,我们测量的是曾经出现在东亚地区在过去几十年最强的粉尘爆发之一。细节描述于 tatarov等。 [2012]。尘羽经过中国,然后向东蔓延到韩国和日本,东南到台湾,甚至达到香港。事件中,据媒体报道,这是在过去70年在韩国最强的沙尘有一个独特的机会,以测试在极端条件下的仪器为我们提供。

tatarov2012cases

减毒反向散射信号,并在面板的体积去极化率的帘曲线以上清楚地示出的灰尘羽流的程度。原位在地面测量显示粉尘浓度(在PM 2.5方面)的高达1000毫克/米3 在本次活动的高峰期。落后的轨迹证实,尘埃羽状的起源是在中亚和灰尘羽已经经过北京造成严重这一城市化地区能见度,交通和人类健康的巨大影响。

Quartz profiles

The profiles above provide a summary of the measurement capabilities of mrs.lea in terms of available data products for dust, which includes backscatter and extinction coefficients, depolarization ratios, lidar ratios and Ångström exponents, and profiles of backscatter coefficients from silicon dioxide. We can infer profiles of mass concentrations of silicon dioxide from lidar measurements if we assume a mixing-ratio of silicon dioxide in mineral dust, which can be inferred from literature and in-situ data and if the source region is known (e.g. from backward trajectory analysis).

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