Similarity Scaling Of Surface-Released Smoke Plumes

Concentration fluctuation data from surface-layer released smokeplumes have been investigated with the purpose of finding suitable scaling parametersfor the corresponding two-particle, relative diffusion process.Dispersion properties have been measured at downwind ranges between 0.1 and 1 km from a continuous, neutrally buoyant ground level source. A combinationof SF₆ and chemical smoke (aerosols) was used as tracer. Instantaneous crosswind concentration profiles of high temporal (up to 55 Hz) and spatialresolution (down to 0.375 m) were obtained from aerosol-backscatter Lidar detectionin combination with simultaneous gas chromatograph (SF₆) reference measurements. The database includes detailed crosswind concentration fluctuation measurements. Each experiment, typically of 1/2-hour duration, containsplume mean and variance concentration profiles, intermittency profiles andexceedence and duration statistics. The diffusion experiments were accompanied by detailed in-situ micrometeorological mean and turbulence measurements. In this paper, a new distance-neighbour function for surface-released smoke plumes is proposed, accompanied by experimental evidence in its support. The new distance-neighbour function is found to scale with the surface-layer friction velocity,and not with the inertial subrange dissipation rate, over the range of distance-neighbour separations considered.     

Studies of Aerosols in The Marine Boundary Layer in the Coastal Area During The EOPACE’99 Campaign

Results are presented based on measurements taken using an FLS-12 lidar system and laser particle counters only on the Atlantic coast of the U.S.A. during a campaign within the scope of the international EOPACE experiment. The objectives of the EOPACE (Electro-optical Propagation Assessment in Coastal Environments) effort, which was conducted in Duck, N.C. (U.S.A.) between 25 February and 11 March 1999, involved investigating, developing and evaluating ocean and coastal aerosol models and their effects on visibility; integrating and developing simple, realistic models for infrared propagation near the ocean surface and developing a consistent chemical/optical model for aerosol particles suitable for inclusion in navy meteorological models.     

中纬度中间层顶钠原子密度高度分布的长期变化趋势研究(2010—2021)

中间层顶/低热层区域(the Mesosphere/Lower Thermosphere,简称MLT)的高度为70~110 km,为了研究这一区域对太阳活动的响应,本文以钠原子为示踪物,对北京延庆(116.0°E,40.5°N)钠共振荧光激光雷达2010年1月—2021年8月近一个太阳活动周期的数据进行了分析,发现钠原子柱密度的长期变化显著,与太阳黑子数的变化呈现出正相关趋势.延庆钠层质心高度的线性趋势在这期间总共上升了311.4±706.6 m,长期变化趋势并不显著.自2018年开始,半高全宽对应的高度范围出现了明显的增加,但是上边沿升高的幅度不大,目前受到广泛关注的热层金属层的观测与研究更依赖于激光雷达探测灵敏度的提升.

     

Lidar点云数据中建筑物的快速提取

Lidar技术可快速获取地表的高精度三维点云数据, 目前对此类数据的分类却是速度慢、精度低, 尤其是城市区域建筑物和树木靠得较近时更是难以准确提取建筑物.介绍了一种基于点云数据生成距离影像, 而后引入对比度纹理辅助的点云数据建筑物快速提取方法.结果证明, 该方法不需要其他辅助数据就能实现点云数据中建筑物的快速提取.      

微脉冲激光雷达反演半干旱区气溶胶消光系数方法

利用位于甘肃省榆中县兰州大学半干旱区气候与环境观测站的微脉冲激光雷达2008年春季的有效观测数据,对微脉冲激光雷达在半干旱区应用时不同反演方法的差别、参数的选取以及反演结果的差异及可能出现的原因进行了讨论。认为Klett法和Fernald法均能反映出大气气溶胶垂直分布的空间和时间特征,且结果较为一致。在晴朗无云及沙尘天气时,两种方法对于低层大气气溶胶消光系数反演结果基本相同,在接近实际探测高度时结果差异较大。有云天气下,Fernald法对于低层气溶胶的消光系数的反演结果同Klett法相比较小,在接近实际探测高度时差异较大。实际应用中,在半干旱地区利用微脉冲激光雷达对气溶胶消光系数进行反演时,对于高层气溶胶的信息获取,采用Klett法更为合理。     

Evaluation of temporal consistency of snow depth drivers of a Rocky Mountain watershed in southern Alberta

Collecting spatially representative data over large areas is a challenge within snow monitoring frameworks. Identifying consistent trends in snow accumulation properties enables increased sampling efficiency by minimizing field collection time and/or remote sensing costs. Seasonal snowpack depth estimations during mid-winter and melt onset conditions were derived from airborne Lidar over the West Castle Watershed in the southern Canadian Rockies on three dates. Each dataset was divided into five sets of snow depth driver classes: elevation, aspect, topographic position index, canopy cover and slope. Datasets were quality controlled by eliminating snow depth values above the 99th percentile value, which had a negligible effect on average snow depths. Consistent trends were observed among driver classes with peak snow accumulation occurring within the treeline ecotone, north-facing aspects, open canopies, topographic depressions and areas with low slope angle. Although mid-winter class trends for each driver were similar and watershed-scale snow depth distributions were significantly correlated (0.76, p < .01), depth distributions within the same driver class of the three datasets were not correlated due to recent snowfall events, redistribution and settling processes. Trends in driver classes during late season melt onset were similar to mid-winter conditions but watershed scale distribution correlation results varied with seasonality (0.68 mid-winter 2014 and melt onset 2016; 0.65 mid-winter 2017 and melt onset 2016, p < .1). This is due to the differing stages of accumulation or ablation and the upward migration in the 0°C isotherm during spring, when snow depth can be declining in valley bottoms while still increasing at higher elevations. The observed consistency in depth driver controls can be used to guide future integrated snow monitoring frameworks.     

Spatial And Temporal Variability Of Mixed-Layer Depth And Entrainment Zone Thickness

Mixed-layer depth and entrainment zone thickness areextracted from two large lidar data sets with arecently developed technique. The entrainment fluxratio (which is often used to model entrainment inatmospheric boundary-layer models) can be calculatedfrom these two quantities. This ratio is generallybelieved to be in the range of 0.1 and 0.4. Aqualitative analysis of time series (MERMOZ II dataset) confirms this range of values under equilibriumconditions (afternoon hours), but also shows that itclearly underestimates the importance of entrainmentduring the morning hours when the mixed layer isgrowing most rapidly. An examination of the spatialdistribution of the entrainment flux ratio (Pacific'93 data set) shows that this parameter is spatiallyhighly variable, even during equilibrium hours inthe afternoon. In regions where the boundary layerhas to adjust to new boundary conditions at theground, values much larger than 0.4 can be observed. Although these results can only be interpretedqualitatively, they suggest that currently usedentrainment parameterisations in boundary-layer modelsare not sufficient to capture the entrainment processproperly.     

激光雷达在沙尘观测中的应用——2004年春季北京和呼和浩特沙尘天气的解析

2004年春季（2003年12月至2004年5月）利用激光雷达在北京和呼和浩特对沙尘天气进行了连续观测。利用激光雷达的数据导出了沙尘和大气污染物气溶胶消光系数的关系,对两个地点的沙尘天气特征和大气污染特征进行了探讨。该期间在呼和浩特观测到较大型的沙尘事件（消光系数大于0.3·km-1）有9次,这些起源于蒙古国/内蒙古的沙尘事件晚于呼和浩特6~10 h在北京被观测到。在呼和浩特观测到的沙尘云块的高度普遍较低（由地表至高空1~2 km）,而在北京较高一般可达到2~4 km,同一沙尘事件的最高浓度（消光系数）是呼和浩特高于北京。在北京观测到的沙尘天气共有17次,其中包括数次小规模的沙尘事件在呼和浩特未观测到。从北京及呼和浩特的观测结果可以看出,北京地区3~5月沙尘的背景浓度高于呼和浩特,北京地区具有明显的区域规模大气污染特征,而呼和浩特只具有局部规模的大气污染特征。     

一种改进的LiDAR数据过滤方法

Lidar的数据过滤是数据预处理的重要步骤,也是获取高精度数字高程模型的关键。现有很多典型的过滤算法都是基于地面种子点逐渐恢复地面的,比如自适应TIN过滤法、迭代线性预测法,分层恢复过滤法等。初始地面种子点选择的好坏将直接反映到过滤结果的精度上,尤其是对丘陵地区的地形恢复,影响更大。本文对基于种子点的TIN三角网加密法(TS过滤算法)进行了深入剖析,并在种子点选择方法上提出了一种基于移动窗口法和最小残差法的混合式种子点选择方法,有效地提高丘陵地区地形恢复的准确度。