Mixed-Layer Depth Determination in the Barcelona Coastal Area From Regular Lidar Measurements: Methods, Results and Limitations

Regular aerosol backscatter measurements using an elastic-backscatter lidar were performed between May 2000 and December 2002 in Barcelona (Spain), within the framework of the European project EARLINET (European Aerosol Research Lidar Network). The mixed-layer depth was one of the major parameters to be retrieved. Three derivative methods have been tested in this complex coastal area using the range-squared-corrected lidar signal: (1) the minimum of its first derivative, (2) the minimum of its second derivative, and (3) the minimum of the first derivative of its logarithm. The second method was found to give statistically the best results when compared to radiosoundings, and was used to process the whole dataset. A number of 162 days and 660 profiles averaged over 30 min have been examined. Between 1000 and 1500 UTC, the mixed-layer depth oscillates between 300 and 1450 m in summer and between 390 and 1420 m in winter. The standard deviation for this portion of the day is 180 and 256 m, respectively, in summer and winter. In summer, low heights (mainly limited to 400–800 m) are associated with large mesoscale compensatory subsidence over the sea and to the thermal internal boundary-layer formation. The strong coastal and orographic influences and the climatological settling of Barcelona determine the complexity of the boundary-layer dynamics and the high heterogeneity of the lidar signals. In many cases, single lidar analyses do not allow an unambiguous determination of the mixed-layer depth. Two diurnal cycle measurements are discussed together with synoptic maps, backtrajectories and radiosoundings in order to outline the complexity of the area and the limitations of the methods.     

Nocturnal Low-Level Jet Characteristics Over Kansas During Cases-99

Characteristics and evolution of the low-level jet (LLJ)over southeastern Kansas were investigated during the 1999 Cooperative Surface-AtmosphereExchange Study (CASES–99) field campaign with an instrument complement consisting of ahigh-resolution Doppler lidar (HRDL), a 60 m instrumented tower, and a triangle of Dopplermini-sodar/profiler combinations. Using this collection of instrumentation we determined thespeed U_X, height Z_X and direction D_X of the LLJ. We investigate here the frequencyof occurrence, the spatial distribution, and the evolution through the night, of these LLJcharacteristics. The jet of interest in this study was that which generates the shear and turbulencebelow the jet and near the surface. This was represented by the lowest wind maximum.We found that this wind maximum, which was most often between 7 and 10 m s¹,was often at or just below 100 m above ground level as measured by HRDL at the CASEScentral site. Over the 60 km profiler–sodararray, the topography varied by 100 m. The wind speed anddirection were relatively constant over this distance (with some tendency for strongerwinds at the highest site), but Z_X was more variable. Z_X was occasionally about equal at allthree sites, indicating that the jet was following the terrain, but more often it seemed to berelatively level, i.e., at about the same height above sea level. Z_X was also more variable thanU_X in the behaviour of the LLJ with time through the night, and on some nights $U_X wasremarkably steady. Examples of two nights with strong turbulence below jet level were furtherinvestigated using the 60 m tower at the main CASES–99 site. Evidence of TKE increasing withheight and downward turbulent transport of TKE indicates that turbulence was primarilygenerated aloft and mixed downward, supporting the upside–down boundary layer notion in thestable boundary layer.     

HNO3 and PSC Measurements from the Transall: Sequestering of HNO3 in the Winter of 1994/95

In the winter of 1994/95 the TRANSALL research aircraft performed several flights in the region of the Arctic vortex during the period of low stratospheric temperatures. The results of simultaneous measurements of HNO3 column amounts by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and of aerosol backscatter profiles by the Ozone Lidar EXperiment (OLEX) are presented for two typical flight scenarios across the polar vortex boundary on December 17, 1994 and January 11/12, 1995. On December 17 and January 12, the column amounts of gaseous HNO3 decreased significantly in regions with low stratospheric temperatures. This decrease was correlated with the extent of the polar stratospheric clouds. Depolarisation measurements showed that type Ib PSCs were observed primarily, but equilibrium calculations for H2SO4/HNO3/H2O aerosols seem to underestimate the observed HNO3 sequestering.     

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.     

复杂城市环境的机载Lidar点云滤波(英文)

A novel filtering algorithm for Lidar point clouds is presented, which can work well for complex cityscapes. Its main features are filtering based on raw Lidar point clouds without previous triangulation or rasterization. 3D topological relations among points are used to search edge points at the top of discontinuities, which are key information to recognize the bare earth points and building points. Experiment results show that the proposed algorithm can preserve discontinuous features in the bare earth and has no impact of size and shape of buildings.     

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.     

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.      

基于机载Lidar的地貌数据快速更新方案研究

空间地理信息作为国家信息资源的重要组成部分之一,承担着越来越重要的作用,地貌数据作为空间数据的组成部分,其数据采集及更新十分重要。机载Lidar问世以来受到测绘行业广泛重视,其应用不断扩展。该文以地貌数据的快速更新为研究目的,深入分析了地貌更新流程以及机载Lidar数据成果,并在此之上提出基于机载Lidar数据的地貌快速更新方案,研究其具体步骤以及核心技术,同时采用CAD二次开发实现地貌更新数据预处理,大幅提高地貌更新效率。     

Multi-level filtering segmentation to measure individual tree parameters based on Lidar data: Application to a mountainous forest with heterogeneous stands

This paper presents a method for individual tree crown extraction and characterisation from a canopy surface model (CSM). The method is based on a conventional algorithm used for localising LM on a smoothed version of the CSM and subsequently for modelling the tree crowns around each maximum at the plot level. The novelty of the approach lies in the introduction of controls on both the degree of CSM filtering and the shape of elliptic crowns, in addition to a multi-filtering level crown fusion approach to balance omission and commission errors. The algorithm derives the total tree height and the mean crown diameter from the elliptic tree crowns generated. The method was tested and validated on a mountainous forested area mainly covered by mature and even-aged black pine (Pinus nigra ssp. nigra [Arn.]) stands. Mean stem detection per plot, using this method, was 73.97%. Algorithm performance was affected slightly by both stand density and heterogeneity (i.e. tree diameter classes’ distribution). The total tree height and the mean crown diameter were estimated with root mean squared error values of 1.83 m and 1.48 m respectively. Tree heights were slightly underestimated in flat areas and overestimated on slopes. The average crown diameter was underestimated by 17.46% on average.     

机载雷达技术在中小比例尺地形图中的应用研究

机载雷达技术已经广泛应用于各个领域,机载雷达能瞬间获得大量的采样点,采样点具有高密度、高精度的优势,本文阐述了机载雷达技术在中小比例尺地形图中的应用。