半椭球形树冠对冠层间隙率与聚集度指数的影响研究

作为森林冠层结构的重要组成部分,树冠形状对冠层间隙率与聚集度指数的计算有重要影响。之前的研究通常将树冠假设为圆锥形、圆柱形、圆锥+圆柱形等形状计算了冠层间隙率与聚集度指数。然而,树冠生长受外部环境以及内部顶端优势等因素的影响,相较于上述理想化的树冠形状,半椭球形更符合树冠自然生长规律。事实上,半椭球形是一种十分常见的树冠形状。本文以树冠在空间呈泊松分布为前提,推导出半椭球形树冠的冠层间隙率与聚集度指数计算公式,并进一步扩展到双半椭球形树冠。同时,以半椭球形树冠为计算基准,对比分析了半椭球形树冠与其他树冠形状冠层间隙率与聚集度指数的相对差异。模拟计算中主要输入参数包括树冠密度、树冠高度、树冠半径以及叶面积指数等。最后通过虚拟场景对结果进行验证。结果表明：（1）半椭球形树冠与其他树冠形状的冠层间隙率有较大差异。随着观测天顶角增加,不同树冠形状与半椭球形树冠的冠层间隙率的相对差异也逐渐增大。当观测天顶角为70°时,圆锥形树冠与半椭球形树冠的冠层间隙率相对差异已接近100%。（2）树冠形状对聚集度指数同样有较明显影响。极端情况下,圆锥形树冠与半椭球形树冠的聚集度指数相对差异达到30%。（3）半椭球形树冠与其他树冠形状的半球空间聚集度指数期望值的差异不容忽视。     

长沙市农村居民点空间格局特征研究

运用2013年长沙市的遥感影像数据,借助于空间插值、空间自相关分析以及空间变差函数等数学模型,对长沙市农村居民点的空间格局进行研究。在空间分布上,长沙市农村居民点空间布局呈现"西密东疏"的特征;在规模分布上,长沙市农村居民点的规模分布存在明显的空间随机独立性及空间分异性特征,并且出现高值聚簇区,主要分布在以浏阳市西北部的焦溪乡、淳口镇、北盛镇、山田乡等地为中心的周边区域;在形态分布上,长沙市农村居民点形态存在显著的空间分异格局,其形态分布的均质程度不高,呈现以中间区域为顶点向周边方向倾斜的结构,空间结构性差异显著,总体上呈随机独立分布状态。     

Effect of particle shape on dust shortwave direct radiative forcing calculations based on MODIS observations for a case study

Assuming spheroidal and spherical particle shapes for mineral dust aerosols, the effect of particle shape on dust aerosol optical depth retrievals, and subsequently on instantaneous shortwave direct radiative forcing (SWDRF) at the top of the atmosphere (TOA), is assessed based on Moderate Resolution Imaging Spectroradiometer (MODIS) data for a case study. Specifically, a simplified aerosol retrieval algorithm based on the principle of the Deep Blue aerosol retrieval method is employed to retrieve dust aerosol optical depths, and the Fu-Liou radiative transfer model is used to derive the instantaneous SWDRF of dust at the TOA for cloud-free conditions. Without considering the effect of particle shape on dust aerosol optical depth retrievals, the effect of particle shape on the scattering properties of dust aerosols (e.g., extinction efficiency, single scattering albedo and asymmetry factor) is negligible, which can lead to a relative difference of at most 5% for the SWDRF at the TOA. However, the effect of particle shape on the SWDRF cannot be neglected provided that the effect of particle shape on dust aerosol optical depth retrievals is also taken into account for SWDRF calculations. The corresponding results in an instantaneous case study show that the relative differences of the SWDRF at the TOA between spheroids and spheres depend critically on the scattering angles at which dust aerosol optical depths are retrieved, and can be up to 40% for low dust-loading conditions.     

雷达强度数据中的阵风锋特征统计和自动识别

利用江苏南京2009-2012年天气雷达数据结合地面自动站风场资料分析江苏沿江地区阵风锋变化特征、阵风锋弧长与移速关系,及其在雷达反射率因子图像中呈现的总体、局部特征,详细分析了三种窄带回波回波带反射率因子分布特征。通过设计反映回波带平坦性的计算方法实现定量分析窄带回波分布异同功能。根据回波带径向波形特征判断径向波形的波宽、波峰个数、波峰阈值和波形双边梯度等特性,实现阵风锋径向波段识别。在对反射率因子图像预处理基础上,结合回波平坦性测试方法和阵风锋径向波形识别算法达到自动识别阵风锋回波的目的。识别效果表明:回波带平均值5 d BZ的独立阵风锋回波识别准确率达87%以上,回波带平均值10 d BZ的混合型阵风锋回波识别准确率达89%以上。对弱阵风锋识别成功率仍较低。     

Effect of leaf distribution pattern on the interception storage capacity of leaf litter under simulated rainfall conditions

Rainwater interception by leaf litter is an important part of forest hydrological processes. The objective of this study was to investigate the interception storage capacity (ISC) of woodland leaf litter for three leaf distribution patterns, one flow path, two flow paths, and three flow paths, manually simulated via one-by-one leaf connection in the top leaf litter layer. A random pattern served as the control. Three different slopes (0°, 5° and 25°, representing flat, gentle and steep slopes, respectively) and two contrasting leaf litters (needle-leaf litter, represented by P. massoniana leaves, and broad-leaf litter, represented by C. camphora leaves) with a biomass of 0.5 kg/m² per unit area were applied, at a rainfall intensity of 50 mm/h. Results suggested that leaf distribution pattern greatly impacts litter drainage and hence affects leaf litter ISC. The delaying capacity of litter drainage initiation and ISC of broad-leaf litter were higher than those of needle-leaf litter under the same slope conditions. The maximum ISC (C_max) and minimum ISC (C_min) of leaf litter at flat and gentle slopes were higher than those at steep slope. C_min of the broad-leaf litter was two times higher than that of needle-leaf litter on average. When raindrops reached the litter layer, some were temporarily intercepted by the top litter layer while others infiltrated leaf litter sublayer along leaf edges, and in the process, some rainwater flowed through litter layer and contributed to lateral litter drainage along the potential flow path formed by leaves. The lateral litter drainage of broad-leaf litter was higher than that of needle-leaf litter, and the partitioning of rainwater into lateral litter drainage increased with increases in slope. The difference in leaf litter C_max among different slopes and leaf shapes decreased with flow path increasing. Therefore, leaf distribution pattern notably impact leaf litter ISC, which is similar to leaf shape and slope impacts. On inclined slopes, avoiding leaf accumulation to form flow path is helpful for improving ISC.     

富氧空气/甲烷对向流扩散火焰的实验研究

为了开发实际适用的富氧燃烧技术,本研究对对向流扩散火焰这一典型的扩散燃烧形态为对象进行实验考查,发现得到的实验结果与作者先前进行的数值模拟结果得到比较好的吻合,即利用详细的基元反应动力学模型对火焰的数值模拟可以很好的再现火焰特性;在此基础上利用CCD成像技术进一步研究了燃料稀释浓度、氧化剂浓度的变化对富氧空气/甲烷对向流扩散火焰形态的影响规律。     

政府地理信息系统的建设和应用

地理信息系统在政府机关的应用形成了政府地理信息系统的专门研兜和应用领域．在论述了政府地理信息系统的基本概念和技术特征之后,重点讨论政府地理信息系统的目标、建设模式、总体设计、薮据库建设、软件系统开发、数据通信及系统应用等。     

Coma Morphology And Constraints On The Rotation Of Comet Hale–Bopp (C/1995 O1)

We present constraints on the spin state of comet Hale-Bopp based on coma morphology. Three cases of rotational states are compatible with near perihelion observations: (1) principal-axis rotation, (2) complex rotational state with a small precessional angle, or (3) complex rotational state with a large ratio between the component periods. For principal axis rotators, images from 1996 (pre-perihelion) are consistent with a rotational angular momentum vector, M, directed at ecliptic longitude and latitude (250°, -5°) while images from late 1997 (post-perihelion) indicate (310°, -40°). This may suggest a change in M. A complex rotational state with small precessional angle requires only a small or no change in M over the active orbital arc. In this case, M is directed near ecliptic longitude and latitude (270°, -20°). A rotationally excited nucleus with a large ratio between component periods requires the nucleus to be nearly spherical. The transformation of dust coma morphology from near-radial jets to bright arcs and then again to near-radial jets is interpreted as a heliocentric and geocentric distance dependent evolutionary sequence. The spiral structures seen in CN filters near perihelion (in contrast to sunward side arcs seen in continuum) can be explained if the precursor of CN molecules (likely sub-micron grains) are emitted from the nucleus at low levels (≈ 10% of the peak daytime emission) during the nighttime. This may be indicative of a nucleus with a CO-rich active area(s). This revised version was published online in July 2006 with corrections to the Cover Date.