基于整体最小二乘的稳健点云数据平面拟合

针对点云数据平面拟合方法没有完整考虑测量数据中的误差及系数阵中误差的情况,提出稳健整体最小二乘点云数据平面拟合方法。该法以整体最小二乘法为基础,在考虑全部观测量存在误差的情况下,通过一定的准则删除数据中的粗差或异常值,从而获得稳健的平面参数估值。实验中,分别利用最小二乘法、特征值法和稳健整体最小二乘拟合法对仿真点云数据和真实点云数据进行平面拟合,结果显示该法能克服异常值的影响,得到可靠的平面参数估值,具有稳健性。     

利用多元LBP特征自动提取城市道路边界

车载移动测量系统可采集高精度道路三维点云数据,为道路边界自动化提取提供了支撑.为解决车载激光点云中城市道路边界点云提取困难问题,本文引入局部二值模式LBP(Local Binary Pattern),针对各类城市道路边界特征,设计了高度LBP、高程离散度LBP和空间形状LBP3种改进算子;构建多元LBP特征语义识别模型...     

Reducing discrepancies in ground and satellite-observed eruption heights

The plume height represents a crucial piece of evidence about an eruption, feeding later assessment of its size, character, and potential impact, and feeding real-time warnings for aviation and ground-based populations. There have been many observed discrepancies between different observations of maximum plume height for the same eruption. A comparison of maximum daily height estimates of volcanic clouds over Indonesia and Papua New Guinea during 1982–2005 shows marked differences between ground and satellite estimates, and a general tendency towards lower height estimates from the ground. Without improvements in the quality of these estimates, reconciled among all available methods, warning systems will be less effective than they should be and the world's record of global volcanism will remain hard to quantify. Examination of particular cases suggests many possible reasons for the discrepancies. Consideration of the satellite and radar cloud observations for the 1991 Pinatubo eruptions shows that marked differences can exist even with apparently good observations. The problem can be understood largely as a sampling issue, as the most widely reported parameter, the maximum cloud height, is highly sensitive to the frequency of observation. Satellite and radar cloud heights also show a pronounced clumping near the height of the tropopause and relative lack of eruptions reaching only the mid-troposphere, reinforcing the importance of the tropopause in determining the eruption height in convectively unstable environments. To reduce the discrepancies between ground and satellite estimates, a number of formal collaboration measures between vulcanological, meteorological and aviation agencies are suggested.     

Improved prediction and tracking of volcanic ash clouds

During the past 30 years, more than 100 airplanes have inadvertently flown through clouds of volcanic ash from erupting volcanoes. Such encounters have caused millions of dollars in damage to the aircraft and have endangered the lives of tens of thousands of passengers. In a few severe cases, total engine failure resulted when ash was ingested into turbines and coating turbine blades. These incidents have prompted the establishment of cooperative efforts by the International Civil Aviation Organization and the volcanological community to provide rapid notification of eruptive activity, and to monitor and forecast the trajectories of ash clouds so that they can be avoided by air traffic. Ash-cloud properties such as plume height, ash concentration, and three-dimensional ash distribution have been monitored through non-conventional remote sensing techniques that are under active development. Forecasting the trajectories of ash clouds has required the development of volcanic ash transport and dispersion models that can calculate the path of an ash cloud over the scale of a continent or a hemisphere. Volcanological inputs to these models, such as plume height, mass eruption rate, eruption duration, ash distribution with altitude, and grain-size distribution, must be assigned in real time during an event, often with limited observations. Databases and protocols are currently being developed that allow for rapid assignment of such source parameters. In this paper, we summarize how an interdisciplinary working group on eruption source parameters has been instigating research to improve upon the current understanding of volcanic ash cloud characterization and predictions. Improved predictions of ash cloud movement and air fall will aid in making better hazard assessments for aviation and for public health and air quality.     

东北冷涡积层混合云系形成条件的个例分析

利用2003年7月7—8日NCEP/NCAR资料和地面高空常规探测资料,利用客观分析的方法,研究了东北冷涡积层混合云系形成的环境条件。结果表明：这一冷涡天气系统是由北部和南部两个低压系统组成,而且均比较深厚,有明显低温区配合。东北地区的降水主要受南部的低压系统影响。该系统有气旋性环流配合,在气旋中心区、气流辐合区和气旋东南侧西南气流中均存在相对湿度高于80%的湿度区。湿度区中含有湿度高于90%的区域,积层混合云系产生在这个区域内,而且降水区与系统的不稳定区和动力场辐合区配合一致。研究表明,东北冷涡天气系统中积层混合云系是在冷涡系统东南部的西南气流中形成的,水汽输送条件较好,而且有高湿不稳定区配合,对研究其生成和发展有指示意义。     

层状云微物理属性垂直分布的季节变化——以新疆地区为例

利用CloudSat卫星资料2B-CLDCLASS和2B-CWC-RVOD数据集,分别揭示了层云与层积云的云粒子等效半径、数浓度及含水量等微物理属性的垂直分布特征及其季节变化规律。结果表明：层云所在的云层高度比层积云高,特别是春季,层云可以延伸到11.0 km处,而层积云云层所在高度最高出现在夏季,最高延伸到8.5 km处。层云中的冰水分布在1.0~11.0 km,液态水分布在0~9.0 km,而层积云的冰水和液态水均分布在0~9.0 km。层云与层积云的冰粒子等效半径、水云粒子数浓度、液态水含量呈现随云层高度的增加而减小的趋势,冰粒子数浓度随云层高度增加呈增大趋势,冰水含量呈峰值分布,峰值出现在6~10 km范围内。各季节层积云粒子等效半径、粒子数浓度及水含量的最大值均大于层云的对应值,从这方面看,层积云更适合作人工增水对象。     

降水性层状云系中过冷水的分布特征

统计分析了降水性层状云系中过冷水出现的频率、过冷水区尺度、云水含量的分布特征,以及云中总的粒子尺度谱,为人工增雨作业提供重要依据。     

H i and optical spectroscopy towards the M15 intermediate-velocity cloud

We present single-dish Arecibo 21-cm H  i observations, covering a 0675×0625 RA–Dec. grid, of the intermediate-velocity cloud (IVC) centred upon the M15 globular cluster. The velocity and positional structure of the IVC gas at V _LSR=70 km s⁻¹ are investigated; it is found to be clumpy and has a peak surface density N _{H  i} ∼8×10¹⁹ cm⁻². Additionally, we have performed a long H  i integration towards HD 203664, a Galactic halo star some 31 from M15, in which optical IVC absorption has previously been detected. No H  i with a velocity exceeding 60 km s⁻¹ was found to a brightness temperature limit of 0.05 K. However, additional pointings did detect IVC gas approximately mid-way between HD 203664 and M15. Finally, we present both Arecibo H  i pointings and low-resolution spectra in the Ca  ii H and K lines towards 15 field stars in the general field towards M15, in an attempt to obtain the distance to the IVC. Intermediate-velocity H  i is detected towards seven sightlines. Stellar spectral types are derived for 12 of the sample. Assuming that these stars lie on the main sequence, their distances are estimated to lie in the range 150≤ d ≤1350 pc. No Ca  ii absorption is observed, either because the IVC is further away than ∼1350 pc or more likely because the gas along these sightlines is of too low a density to be detected by the current observations.     

Star formation in unbound giant molecular clouds: the origin of OB associations?

We investigate the formation of star clusters in an unbound giant molecular cloud, where the supporting kinetic energy is twice as large as the cloud's self-gravity. This cloud manages to form a series of star clusters and disperse, all within roughly two crossing times (10 Myr), supporting recent claims that star formation is a rapid process. Simple assumptions about the nature of the star formation occurring in the clusters allows us to place an estimate for the star formation efficiency at about 5–10 per cent, consistent with observations. We also propose that unbound clouds can act as a mechanism for forming OB associations. The clusters that form in the cloud behave as OB subgroups. These clusters are naturally expanding from one another due to the unbound nature of the flows that create them. The properties of the cloud we present here are consistent with those of classic OB associations.     

Dense cores in the L1630 molecular cloud: discovering new protostars with SCUBA

Maps of the 450- and 850-μm dust continuum emission from three star-forming condensations within the Lynds 1630 molecular cloud, made with the SCUBA bolometer array, reveal the presence of four new submillimetre sources, each of a few solar masses (two of which are probably class I and two of which are class 0), as well as several sources the existence of which was previously known. The sources are located in filaments and appear elongated when observed at 450 μm. They probably have dust temperatures in the range 10 to 20 K, in good agreement with previous ammonia temperature estimates. Attempts to fit their structures with power-law and Gaussian density distributions suggest that the central distribution is flatter than expected for a simple singular isothermal sphere.
Although the statistics are poor, our results suggest that the ratio of 'protostellar core' mass to total virial mass may be similar for both large and small condensations.