有关地形通视分析问题的研究和探讨     

田金蓉  汉斯 《测绘学院学报》1992,(3)

本文通过对地形通视分析的基本设想的描述及其实践途径中有关问题的探讨,结合实例阐明了计算机自动进行通视分析的基本方法和处理技巧,并附有具体程序。  相似文献   

佛山市近30年来能见度变化趋势的分析   总被引：3，自引：0，他引：3  

张军 《地理研究》1993,12(4):54-61

本文分析了近30年来各季能见度≤4或10km出现时数的变化趋势。结果表明,佛山市能见度呈加速恶化的趋势。能见度的变化趋势与相对湿度关系不大,但与地面风向却有明显的关系。  相似文献   

Cartographically Wordy but not Necessarily Worthy     

《The Cartographic journal》2013,50(3):195-197

Abstract

A novel method called multidirectional visibility index (MVI) has been developed and verified. The MVI improves standard cartographic analytical shading with a number of enhancements to topographic detail and prominent structures, i.e. the portrayal of flat areas in lighter tones, the accentuation of morphologic edges, and the multiscale visualisation of morphologic terrain features. The procedure requires a digital elevation model (DEM) and involves the following steps: visibility mask computation; the respective multidirectional altering of the azimuth and elevation angle; the generation of continuous grid MVIs that indicate upper/lower views, quasi-slope, and relative relief; and an appropriate visualisation of the relevant MVI as a standalone technique or in combination with standard hill-shaded relief. The modelling parameters are robust and therefore highly adaptive to different landforms.  相似文献   

Automatic generation of the axial lines of urban environments to capture what we perceive     

Bin Jiang  Xintao Liu 《International journal of geographical information science》2013,27(4):545-558

Based on the concepts of isovists and medial axes, we developed a set of algorithms that can automatically generate axial lines for representing individual linearly stretched parts of open space of an urban environment. Open space is the space between buildings where people can freely move around. The generation of the axial lines has been a key aspect of space syntax research, conventionally relying on hand-drawn axial lines of an urban environment, often called axial map, for urban morphological analysis. Although various attempts have been made towards an automatic solution, few of them can produce the axial map that consists of the least number of longest visibility lines, and none of them really works for different urban environments. Our algorithms provide a better solution than existing ones. Throughout this article, we have also argued and demonstrated that the axial lines constitute a true skeleton, superior to medial axes, in capturing what we perceive about the urban environment.  相似文献   

Incorporating vegetation into visual exposure modelling in urban environments     

P. Bartie  F. Reitsma  S. Kingham  S. Mills 《International journal of geographical information science》2013,27(5):851-868

Visual exposure modelling establishes the extent to which a nominated feature may be seen from a specified location. The advent of high-resolution light detection and ranging (LiDAR)-sourced elevation models has enabled visual exposure modelling to be applied in urban regions, for example, to calculate the field of view occupied by a landmark building when observed from a nearby street. Currently, visual exposure models access a single surface elevation model to establish the lines of sight (LoSs) between the observer and the landmark feature. This is a cause for concern in vegetated areas where trees are represented as solid protrusions in the surface model totally blocking the LoSs. Additionally, the observer's elevation, as read from the surface model, would be incorrectly set to the tree top height in those regions. The research presented here overcomes these issues by introducing a new visual exposure model, which accesses a bare earth terrain model, to establish the observer's true elevation even when passing through vegetated regions, a surface model for the city profile and an additional vegetation map. Where there is a difference between terrain and surface elevations, the vegetation map is consulted. In vegetated areas the LoS is permitted to continue its journey, either passing under the canopy with clear views or partially through it depending on foliage density, otherwise the LoS is terminated. This approach enables landmark visual exposure to be modelled more realistically, with consideration given to urban trees. The model's improvements are demonstrated through a number of real-world trials and compared to current visual exposure methods.  相似文献   

双通道能见度自动测量仪研究   总被引：1，自引：0，他引：1  

冶林茂  王道远  王艳斌 《气象与环境科学》2012,35(2):83-86

从透射和散射的原理出发,推导了基于红外测量的双通道能见度仪的工程测量方程,比较了单通道和双通道能见度测量仪的性能,结果表明,双通道能见度测量仪具有精度高、性能稳定、使用可靠、维护量小的特点。  相似文献   

环渤海地区大气低能见度气候特征及影响因子分析   总被引：2，自引：0，他引：2  

郝天依  王式功  尚可政  佘峰 《气象》2012,38(9):1087-1095

利用环渤海地区地面和高空观测资料,统计分析了该地区大气低能见度出现频率的时空分布特征及各相关气象因子的变化情况。结果表明:该地区大气低能见度出现频率年际变化特征表现为弱的上升趋势和周期振荡,主要周期为2、4和6～8 a;月际变化特征为双峰型,高峰值出现在夏季的7月,次峰值为冬季的12月,一天中的08时刻最易出现大气低能见度,整个地区大气低能见度出现频率的空间分布存在较大的不一致性;根据各季节大气低能见度出现频率空间分布特征的不同将整个地区分为三个区域,Ⅰ区包括渤海湾东北角的辽宁靠近黄海的小部分地区及渤海西北面的辽宁与河北毗邻的一部分地区,Ⅱ区包括渤海北部的辽宁小部分地区和京冀大部地区及南部的鲁北部等地区,Ⅲ区为黄海沿岸地区,各区高湿度、小风速是造成大气低能见度的相对重要的气象条件;大气低能见度出现前期或同时刻,低层基本都会维持一个逆温层或等温层和湿层。  相似文献   

一次广东省大雾过程的数值模拟分析   总被引：1，自引：0，他引：1  

樊琦  王东海  黄聪敏  范绍佳  王安宇  冯瑞权 《热带气象学报》2009,25(5):589-595

利用美国国家大气研究中心（NCAR）和宾夕法尼亚州立大学联合研制的第5代中尺度气象模式系统MM5,对广东省地区春季出现的一次大雾过程进行了数值模拟研究。模式模拟结果与实际温湿探空的对比表明,模式很好地模拟了大雾过程的流场变化特征及表征大雾的液态水含量分布。对这次大雾生消过程起决定性作用的是925 hPa风场的变化。当925 hPa转为偏南风控制时,暖湿的海洋性空气流经较冷的下垫面从而形成大范围的平流雾;而当925 hPa转为干冷的偏北风控制时,原本形成的大雾很快就消散了。同时模式也很好地模拟了伴随此次平流雾出现的逆温过程。逆温层高度约在900 hPa附近,具有相当的厚度,这对于大雾的形成和维持有一定作用。另外,利用模式模拟的液态水含量值估算的能见度水平分布情况与实况的观测结果也较为一致。  相似文献   

小洋山岛大气气溶胶光学厚度的特征分析     

贾盛洁  刘锦丽  吕达仁  杜秉玉 《气候与环境研究》2009,14(4):427-433

小洋山岛位于上海东南面距海岸线约30km处,四面环海,研究其上空的大气气溶胶光学特性对了解我国东部沿海地区及其近海海域的环境和气候影响等都具有重要的意义。对于近岸海岛的气溶胶光学厚度(AOD)观测,至今国内尚未见这方面的实测资料与分析。本次实验利用2006～2007年连续观测得到的AOD值,分析了AOD的季节变化及其与地面风向、湿度和能见度等气象要素的关系,并给出了气溶胶消光谱。分析发现:小洋山地区AOD具有春季最大,冬季次之,秋季较小的特点,而且在低能见度情况下,气溶胶以大粒子为主;盛行西风时,AOD值增大且大粒子比重增加;AOD与湿度有较好的正相关关系。  相似文献   

华南沿海地区太阳直接辐射、能见度及大气气溶胶变化特征分析   总被引：26，自引：5，他引：21  

罗云峰  吕达仁  何晴  王凡 《气候与环境研究》2000,5(1):36-44

分析了中国华南地区福州、广州、海口、南宁等地1961～1990年太阳直接辐射总量、日照时数、总云量、大气能见度和地面水汽压等资料,并利用这些资料反演了该地区大气气溶胶的光学厚度值。结果表明：近30年来,华南地区太阳直接辐射总量和日照时数呈明显下降趋势。与60年代相比,80年代各站太阳直接辐射总量的年平均值均下降20%以上,其中广州下降29.2%;日照时数,广州减少了1.1 h,福州1 h,南宁0.9 h,海口0.5 h。分析发现,造成下降的原因不是由于云量或大气中水汽含量的变化,而是由于地面能见度的明显减小和大气气溶胶的增加。4站中,14时地面能见度均以夏季最好,最高值出现在7月;而地面能见度最差的季节海口、南宁两站在冬季,福州和广州两站在春季3、4月份。相比较而言,海口能见度最好,福州和南宁次之,广州最差。4站大气气溶胶光学厚度值的大小、年及季节变化与地面能见度有密切的关系,但两者不尽一致,因此,在研究气溶胶的辐射和气候效应时必须合理地考虑中高层大气气溶胶的分布。  相似文献