合肥地区气溶胶光学特性的地基观测研究

利用自主研制的DTF-5型太阳辐射计观测合肥地区2008年10月—2010年5月的太阳直接辐射消光,反演合肥地区气溶胶光学厚度、Angstrom参数和沙尘天气过程中的粒子谱分布,并对结果进行分析。结果表明:合肥地区气溶胶光学厚度季节变化除气候因素外,受人为因素影响明显,季节变化规律复杂。总体上秋季较小,冬春季节持续增大,夏季较平稳。而Angstrom参数与气溶胶光学厚度大致呈反相关,秋冬上升,春季骤降,夏季平稳值较大。气溶胶光学厚度日变化大致可分为4种类型:日变化相对稳定;整体呈上升趋势;整体呈下降趋势;一日内出现一到多个峰值。其中第四种类型出现几率最大。沙尘天气过程中,气溶胶光学厚度和Angstrom参数分别呈现出"谷-峰-谷"、"峰-谷-峰"的变化规律,其中Angstrom参数在沙尘影响严重时甚至出现负值。半径为0.2~1.0μm的大粒子和大于1.0μm的巨粒子浓度在沙尘天气过程中大幅增加。     

偏振微脉冲激光雷达对一次沙尘过程的探测分析

为研究沙尘暴的垂直分布及变化过程,在介绍偏振微脉冲激光雷达原理的基础上展示了自主研发的雷达系统。利用该系统监测了一次沙尘暴过程,通过分析这次沙尘过程的变化特点,认为此次过程包含有地面扬沙和高空输送两部分。数据分析表明,偏振微脉冲激光雷达具有较强的沙尘探测能力,可以直接反映沙尘垂直结构的分布状况和演变特征。     

沙尘和灰霾天气下毛乌素沙漠地区大气气溶胶的光学特征

利用AERONET榆林站点的数据比较分析了在沙尘和灰霾两种不同天气条件下毛乌素沙漠边缘地区大气气溶胶的光学和物理特性。分析的主要内容包括:气溶胶光学厚度、单次散射反照率、复折射指数、不对称因子、气溶胶粒子的粒度分布、Angstrom波长指数、体积浓度、气溶胶粒子半径等光学和物理参数。分析结果表明,榆林地区大气气溶胶光学特性主要是受到沙尘和人为气溶胶的共同影响。在沙尘天气和灰霾天气下,大气气溶胶的光学特性有显著的差异。     

沙尘和灰霾天气下毛乌素沙漠地区大气气溶胶的光学特征

利用AERONET榆林站点的数据比较分析了在沙尘和灰霾两种不同天气条件下毛乌素沙漠边缘地区大气气溶胶的光学和物理特性.分析的主要内容包括:气溶胶光学厚度、单次散射反照率、复折射指数、不对称因子、气溶胶粒子的粒度分布、Angstrom波长指数、体积浓度、气溶胶粒子半径等光学和物理参数.分析结果表明,榆林地区大气气溶胶光学特性主要是受到沙尘和人为气溶胶的共同影响.在沙尘天气和灰霾天气下,大气气溶胶的光学特性有显著的差异.     

Ag_2S纳米粒子的合成与表征

以油酸钠为表面活性剂、硝酸银和硫脲为反应物,在甲苯-水两相界面处合成了Ag_2S纳米粒子。采用紫外-可见吸收光谱(UV-Vis)、透射电子显微镜(TEM)和广角X射线衍射(WAXD)等方法对Ag_2S纳米粒子的光学性质、形貌及晶体结构进行了表征。结果表明,通过改变甲苯-水两相界面反应体系的条件,可以得到粒子尺寸窄分布的Ag_2S纳米粒子;WAXD测定表明所合成的Ag_2S纳米粒子具有单斜结构。     

两种方法测量大气气溶胶折射率的对比分析

针对气溶胶折射率在分析大气气溶胶光学特性中的重要性,介绍两种综合利用黑碳仪、浊度计、光学粒子计数器和微脉冲激光雷达测量大气气溶胶折射率的新方法。两种方法都是根据球形粒子的Mie散射理论计算大气气溶胶的折射率,使用以上两种方法对厦门地区气溶胶折射率进行了计算和对比分析,证明了它们的合理性,分析了它们的测量精度和误差来源。     

单分散Fe3O4@SiO2/Au复合纳米颗粒的制备

制备了尺寸为30nm,具有磁响应的单分散Fe3O4@SiO2/Au核壳纳米颗粒,并研究其光学性质。首先利用热分解法制备油酸修饰的Fe3O4纳米粒子,再用反相微乳法制备Fe3O4@SiO2纳米粒子,最后利用表面修饰的氨基还原性,获得Fe3O4@SiO2/Au核壳复合纳米颗粒。分别用TEM、XRD、Zeta电位与粒度分析仪对产物形貌、结构、表面电位和粒径分布进行表征,用紫外-可见分光光度计对光学性质进行了测试。     

2.5D激光传感器设计及室内环境特征提取算法研究

在机器人同步定位与地图构建(Simultaneous Localization and Mapping,SLAM)问题中,机器人一般通过激光雷达或视觉传感器来感知环境。视觉传感器受环境光照影响很大,相比之下激光传感器具有测距精度高、性能稳定的优点。为改进普通2D激光雷达数据量小、在SLAM的数据匹配过程中鲁棒性不强的问题,本文设计了一种音圈电机驱动的2. 5D激光传感器。采用电机驱动2D激光雷达在竖直方向上往复运动,通过对2D激光数据和音圈电机编码器的同步实现了空间带状(2. 5D)区域的激光数据采集。当移动机器人工作在半结构化的室内环境中时,可以认为从2. 5D激光传感器获得的高度有限的带状点云具有与地面垂直的先验分布。本文对2. 5D激光传感器采集到的激光点云进行了特征的提取,提取了空间的平面和棱线特征以及竖直方向突变的特征。     

基于地基激光雷达数据的单木结构参数提取研究

针对利用地基激光雷达数据提取单木结构参数的问题,提出了一套较为复杂林分条件下的地基激光雷达数据获取方案与单木结构参数提取方法。首先利用八邻点距离检验法对点云数据中的多次散射点进行滤除,进而通过对现有的变尺度地面点识别方法进行改进,实现了对研究区内的地面点云的快速识别。通过对地基激光雷达数据的分析,提出了一种基于树干点云垂直连续分布特征的树干识别方法,在此基础上提取了单木位置、胸径和树高,最后将所提取的结构参数与林业测量数据进行了对比,结果具有较好的一致性。     

地面气溶胶集成观测系统

介绍一种地面气溶胶集成观测系统的设计思路和集成方法,采用浊度仪、吸收光度计、粒子计数器、粒径谱仪、碳黑仪等仪器观测气溶胶的散射和吸收特性、黑碳浓度、粒径分布和粒子数浓度等。结果表明,测量吸收特性和粒子数浓度的仪器位于测量散射特性的仪器之后,仪器之间可以互相对比验证;将测量气溶胶吸收特性的仪器和黑碳仪"并联",可以观测到更多气溶胶特性信息;测量气溶胶粒径分布及粒子数浓度的仪器可以结合使用,也可以单独分开或"并联"综合观测;仪器综合集成观测的前提是保证仪器流量分配正确,切割头流量达到要求的范围,保证切割效率。     

Determination of cloud effective particle size from the multiple-scattering effect on lidar integration-method temperature measurements

A method is presented that permits the determination of the cloud effective particle size from Raman- or Rayleigh-integration temperature measurements that exploits the dependence of the multiple-scattering contributions to the lidar signals from heights above the cloud on the particle size of the cloud. Independent temperature information is needed for the determination of size. By use of Raman-integration temperatures, the technique is applied to cirrus measurements. The magnitude of the multiple-scattering effect and the above-cloud lidar signal strength limit the method's range of applicability to cirrus optical depths from 0.1 to 0.5. Our work implies that records of stratosphere temperature obtained with lidar may be affected by multiple scattering in clouds up to heights of 30 km and beyond.     

Improved retrievals of the optical properties of cirrus clouds by a combination of lidar methods

We focus on improvement of the retrieval of optical properties of cirrus clouds by combining two lidar methods. We retrieve the cloud's optical depth by using independently the molecular backscattering profile below and above the cloud [molecular integration (MI) method] and the backscattering profile inside the cloud with an a priori effective lidar ratio [particle integration (PI) method]. When the MI method is reliable, the combined MI-PI method allows us to retrieve the optimal effective lidar ratio. We compare these results with Raman lidar retrievals. We then use the derived optimal effective lidar ratio for retrieval with the PI method for situations in which the MI method cannot be applied.     

Error analysis of Raman differential absorption lidar ozone measurements in ice clouds

A formalism for the error treatment of lidar ozone measurements with the Raman differential absorption lidar technique is presented. In the presence of clouds wavelength-dependent multiple scattering and cloud-particle extinction are the main sources of systematic errors in ozone measurements and necessitate a correction of the measured ozone profiles. Model calculations are performed to describe the influence of cirrus and polar stratospheric clouds on the ozone. It is found that it is sufficient to account for cloud-particle scattering and Rayleigh scattering in and above the cloud; boundary-layer aerosols and the atmospheric column below the cloud can be neglected for the ozone correction. Furthermore, if the extinction coefficient of the cloud is ?0.1 km(-1), the effect in the cloud is proportional to the effective particle extinction and to a particle correction function determined in the limit of negligible molecular scattering. The particle correction function depends on the scattering behavior of the cloud particles, the cloud geometric structure, and the lidar system parameters. Because of the differential extinction of light that has undergone one or more small-angle scattering processes within the cloud, the cloud effect on ozone extends to altitudes above the cloud. The various influencing parameters imply that the particle-related ozone correction has to be calculated for each individual measurement. Examples of ozone measurements in cirrus clouds are discussed.     

Simulations of the observation of clouds and aerosols with the Experimental Lidar in Space Equipment system

We carried out a simulation study for the observation of clouds and aerosols with the Japanese Experimental Lidar in Space Equipment (ELISE), which is a two-wavelength backscatter lidar with three detection channels. The National Space Development Agency of Japan plans to launch the ELISE on the Mission Demonstrate Satellite 2 (MDS-2). In the simulations, the lidar return signals for the ELISE are calculated for an artificial, two-dimensional atmospheric model including different types of clouds and aerosols. The signal detection processes are simulated realistically by inclusion of various sources of noise. The lidar signals that are generated are then used as input for simulations of data analysis with inversion algorithms to investigate retrieval of the optical properties of clouds and aerosols. The results demonstrate that the ELISE can provide global data on the structures and optical properties of clouds and aerosols. We also conducted an analysis of the effects of cloud inhomogeneity on retrievals from averaged lidar profiles. We show that the effects are significant for space lidar observations of optically thick broken clouds.     

Lidar ratio and depolarization ratio for cirrus clouds

We report on studies of the lidar and the depolarization ratios for cirrus clouds. The optical depth and effective lidar ratio are derived from the transmission of clouds, which is determined by comparing the backscattering signals at the cloud base and cloud top. The lidar signals were fitted to a background atmospheric density profile outside the cloud region to warrant the linear response of the return signals with the scattering media. An average lidar ratio, 29 +/- 12 sr, has been found for all clouds measured in 1999 and 2000. The height and temperature dependences ofthe lidar ratio, the optical depth, and the depolarization ratio were investigated and compared with results of LITE and PROBE. Cirrus clouds detected near the tropopause are usually optically thin and mostly subvisual. Clouds with the largest optical depths were found near 12 km with a temperature of approximately -55 degrees C. The multiple-scattering effect is considered for clouds with high optical depths, and this effect lowers the lidar ratios compared with a single-scattering condition. Lidar ratios are in the 20-40 range for clouds at heights of 12.5-15 km and are smaller than approximately 30 in height above 15 km. Clouds are usually optically thin for temperatures below approximately -65 degrees C, and in this region the optical depth tends to decrease with height. The depolarization ratio is found to increase with a height at 11-15 km and smaller than 0.3 above 16 km. The variation in the depolarization ratio with the lidar ratio was also reported. The lidar and depolarization ratios were discussed in terms of the types of hexagonal ice crystals.     

In-line type micropulse lidar with an annular beam: experiment

An in-line type compact micropulse lidar (MPL) with an annular beam was developed for low-altitude cloud measurement. An optical circulator and a couple of axicon prisms for an annular beam were installed on the lidar optics. The advantage of using the in-line MPL is its ability to obtain a near-range measurement with a narrow field of view of 0.1 mrad and to obtain a depolarization measurement of the orthogonally polarized echoes caused by ice crystals of a low-altitude cloud. The total insertion loss of the lidar optics was 3 dB. Detectors such as avalance photodiode detectors can be operated in an analog mode near the breakdown voltage because of the high isolation of the optical circulator. The ideal lidar echo variation from the nearest distance was verified by measuring the mountain echoes at various distances. The depolarization measurement of a low-altitude ice cloud was also demonstrated.     

Classification of particle effective shape ratios in cirrus clouds based on the lidar depolarization ratio

A shape classification technique for cirrus clouds that could be applied to future spaceborne lidars is presented. A ray-tracing code has been developed to simulate backscattered and depolarized lidar signals from cirrus clouds made of hexagonal-based crystals with various compositions and optical depth, taking into account multiple scattering. This code was used first to study the sensitivity of the linear depolarization rate to cloud optical and microphysical properties, then to classify particle shapes in cirrus clouds based on depolarization ratio measurements. As an example this technique has been applied to lidar measurements from 15 mid-latitude cirrus cloud cases taken in Palaiseau, France. Results show a majority of near-unity shape ratios as well as a strong correlation between shape ratios and temperature: The lowest temperatures lead to high shape ratios. The application of this technique to space-borne measurements would allow a large-scale classification of shape ratios in cirrus clouds, leading to better knowledge of the vertical variability of shapes, their dependence on temperature, and the formation processes of clouds.     

Multiple-scattering lidar retrieval method: tests on Monte Carlo simulations and comparisons with in situ measurements

A multiple-field-of-view (MFOV) lidar measurement and solution technique has been developed to exploit the retrievable particle extinction and size information contained in the multiple-scattering contributions to aerosol lidar returns. We describe the proposed solution algorithm. The primary retrieved parameters are the extinction coefficient at the lidar wavelength and the effective particle diameter from which secondary products such as the extinction at other wavelengths and the liquid-water content (LWC) of liquid-phase clouds can be derived. The solutions are compared with true values in a series of Monte Carlo simulations and with in-cloud measurements. Good agreement is obtained for the simulations. For the field experiment, the retrieved effective droplet diameter and LWC for the available seven cases studied are on average 15% and 35% (worst case) smaller than the measured data, respectively. In the latter case, the analysis shows that the differences cannot be attributed solely to lidar inversion errors. Despite the limited penetration depth (150-300 m) of the lidar pulses, the results of the studied cases indicate that the retrieved lidar solutions remain statistically representative of measurements performed over the full cloud extent. Long-term MFOV lidar monitoring could thus become a practical and economical option for cloud statistical studies but more experimentation on more varied cloud conditions, especially for LWC, is still needed.     

GLITTER: new lidar technique for cloud-base altimetry. Description and initial aircraft measurements

Knowledge of cloud-base heights is important for climate studies, weather, and military operations. Conventional lidar methods monitor cloud depths by direct transmission of the beam through the cloud and sensing the backscattered returns. These techniques are limited by severe optical scattering by cloud particles to thickness <0.5 km. We have conceived of a novel lidar method measurement for thick-cloud-base altimetry from above that is not restricted by cloud scattering. The new method, known as GLITTER (an acronym for glimpses of the lidar images through the empty regions), relies on cloud porosity and diffuse reflection from land features to sense cloud bottoms. An aircraft GLITTER lidar measured cloud bases at 3.7- and 4.5-km altitudes. These initial results represent a proof-of-principle demonstration of the new lidar method.     

Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations

A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.