Investigation of Uncertainties of Establishment Schemes in Dynamic Global Vegetation Models简     

SONG Xiang  ZENG Xiaodong 《大气科学进展》2014,31(1):85-94

In Dynamic Global Vegetation Models （DGVMs）, the establishment of woody vegetation refers to flowering, fertiliza- tion, seed production, germination, and the growth of tree seedlings. It determines not only the population densities but also other important ecosystem structural variables. In current DGVMs, establishments of woody plant functional types （PFTs） are assumed to be either the same in the same grid cell, or largely stochastic. We investigated the uncertainties in the competition of establishment among coexisting woody PFTs from three aspects： the dependence of PFT establishments on vegetation states; background establishment; and relative establishment potentials of different PFTs. Sensitivity experi- ments showed that the dependence of establishment rate on the fractional coverage of a PFT favored the dominant PFT by increasing its share in establishment. While a small background establishment rate had little impact on equilibrium states of the ecosystem, it did change the timescale required for the establishment of alien species in pre-existing forest due to their disadvantage in seed competition during the early stage of invasion. Meanwhile, establishment purely fiom background （the scheme commonly used in current DGVMs） led to inconsistent behavior in response to the change in PFT specification （e.g., number of PFTs and their specification）. Furthermore, the results also indicated that trade-off between irtdividual growth and reproduction/colonization has significant influences on the competition of establishment. Hence, further development of es- tablishment parameterization in DGVMs is essential in reducing the uncertainties in simulations of both ecosystem structures and successions.  相似文献   

Preliminary Assessment of the Common Land Model Coupled with the IAP Dynamic Global Vegetation Model          下载免费PDF全文

ZHU Jia-Wen  ZENG Xiao-Dong  LI Fang  SONG Xiang 《大气和海洋科学快报》2014,7(6):505-509

The Common Land Model（CoLM） was coupled with the IAP Dynamic Global Vegetation Model（IAPDGVM）, and the performance of this combined CoLMIAP model was evaluated. Offline simulations using both the original Common Land Model（CoLM-LPJ） and CoLM-IAP were conducted. The CoLM-IAP coupled model showed a significant improvement over CoLMLPJ, as the deciduous tree distribution decreased over temperate and boreal regions, while the distribution of evergreen trees increased over the tropics. Some biases in CoLM-LPJ were preserved, including the overestimation of evergreen trees in tropical savanna, the underestimation of boreal evergreen trees, and the absence of boreal shrubs. However, most of these biases did not exist in a further coupled simulation of IAP-DGVM with the Community Land Model（CLM）, for which the parameters of IAP-DGVM were optimized. This implies that further improvement is needed to deal with the differences between CoLM and CLM in parameterizations of landbased physical and biochemical processes.  相似文献   

基于Auto CAD扩展属性的多边形面积统计汇总应用     

郭振华  薛兰格 《北京测绘》2014,(3):57-60,56

提出在不规则多边形面积统计汇总工作中应用基于Auto CAD扩展属性的技术,对多边形的对象属性进行存储,将多边形图形数据与属性数据一体化结合,实现了多边形图形多元化处理,如统计分析、汇总报表、图形标注等的自动化、智能化,为不规则多边形面积处理提出了一种较新的处理思路。本文结合工程实例,通过对比分析详细介绍了该技术的具体应用过程。  相似文献   

Google Earth Engine平台下秦岭地区植被覆盖时空变化分析     

赵侃  师芸  牛敏杰 《测绘通报》2022,(5):49-55

秦岭地区植被覆盖动态变化对其生态环境有重要影响。本文利用Google Earth Engine云平台,选取1986—2019年Landsat TM/OLI地表反射率数据,结合像元二分模型估算秦岭地区植被覆盖度(FVC);通过年际变化斜率、变异系数、Hurst指数等评价指标,对FVC的时空变化、稳定性和持续性变化进行分析。此外,探究FVC与气温、降雨的耦合关系,并分析土地利用变化对FVC的影响。结果表明:34年间,秦岭地区FVC整体上呈现良好的状况,中高等及以上植被覆盖区达73.11%;FVC由1986年的62.86%增长到2019年的70.01%,植被活动在不断增强;FVC的变异系数均值为0.34,标准差为0.45,其稳定性与其空间分布呈高度自相关性;秦岭地区的植被覆盖变化受气候变化和人为因素的共同影响。  相似文献   

基于地面试验的植被覆盖率估算模型及其影响因素研究   总被引：1，自引：0，他引：1  

田静  苏红波  孙晓敏  陈少辉 《国土资源遥感》2009,(3):1-6

以植被覆盖率的遥感反演为研究主线,以玉米作物为例,在基于地面试验获得作物光谱、叶面积指数和多角度覆盖率的基础上,对目前普遍采用的两种基于植被指数的植被覆盖率估算模型进行了精度比较,同时对植被覆盖率反演的影响因子(叶面积指数、植被空间分布和观测角度)进行了分析.由此得到:估算植被覆盖率的最优植被指数为归一化植被指数;叶面积指数对植被指数与植被覆盖率间关系的影响随植被的生长不断增大;植被空间分布对垂直覆盖率的估算影响很小.对于多角度覆盖率有这样的规律,即在4种空间分布下,以0°观测天顶角(VZA)为中心,在相反方位角上随VZA的增加,覆盖率值基本呈对称分布;在玉米刚出苗时,覆盖率随VZA的增加而增加,当VZA=0°时达到最小值,而随着玉米的进一步生长,4种分布条件下覆盖率随VZA的增加反而降低,在VZA=0°时达到最大值.  相似文献   

CLOUD RADIATIVE AND MICROPHYSICAL EFFECTS ON THE RELATION BETWEEN SPATIAL MEAN RAIN RATE, RAIN INTENSITY AND FRACTIONAL RAINFALL COVERAGE     

张晓怡  张子涵  李小凡 《热带气象学报(英文版)》2018,24(3):346-355

Cloud radiative and microphysical effects on the relation between spatial mean rain rate, rain intensity and fractional rainfall coverage are investigated in this study by conducting and analyzing a series of two-dimensional cloud resolving model sensitivity experiments of pre-summer torrential rainfall in June 2008. The analysis of time-mean data shows that the exclusion of radiative effects of liquid clouds reduces domain mean rain rate by decreasing convective rain rate mainly through the reduced convective-rainfall area associated with the strengthened hydrometeor gain in the presence of radiative effects of ice clouds, whereas it increases domain mean rain rate by enhancing convective rain rate mainly via the intensified convective rain intensity associated with the enhanced net condensation in the absence of radiative effects of ice clouds. The removal of radiative effects of ice clouds decreases domain mean rain rate by reducing stratiform rain rate through the suppressed stratiform rain intensity related to the suppressed net condensation in the presence of radiative effects of liquid clouds, whereas it increases domain mean rain rate by strengthening convective rain rate mainly via the enhanced convective rain intensity in response to the enhanced net condensation in the absence of radiative effects of liquid clouds. The elimination of microphysical effects of ice clouds suppresses domain mean rain rate by reducing stratiform rain rate through the reduced stratiform-rainfall area associated with severely reduced hydrometeor loss.  相似文献   

Geomorphology-oriented digital terrain analysis: Progress and perspectives   总被引：1，自引：1，他引：0  

XIONG Liyang  TANG Guoan  YANG Xin  LI Fayuan 《地理学报(英文版)》2021,31(3):456-476

Digital terrain analysis(DTA) is one of the most important contents in the research of geographical information science(GIS). However, on the basis of the digital elevation model(DEM), many problems exist in the current research of DTA in geomorphological studies. For instance, the current DTA research appears to be focused more on morphology, phenomenon, and modern surface rather than mechanism, process, and underlying terrain. The current DTA research needs to be urgently transformed from the study of landform morphology to one focusing on landform process and mechanism. On this basis, this study summarizes the current research status of geomorphology-oriented DTA and systematically reviews and analyzes the research about the knowledge of geomorphological ontology, terrain modeling, terrain derivative calculation, and terrain analytical methods. With the help of DEM data, DTA research has the advantage of carrying out geomorphological studies from the perspective of surface morphology. However, the study of DTA has inherent defects in terms of data expression and analytic patterns. Thus, breakthroughs in basic theories and key technologies are necessary. Moreover, scholars need to realize that DTA research must be transformed from phenomenon to mechanism, from morphology to process, and from terrain to landform. At present, the research development of earth science has reached the critical stage in which the DTA research should focus more on geomorphological ontology. Consequently, this study proposes several prospects of geomorphology-oriented DTA from the aspects of value-added DEM data model, terrain derivatives and their spatial relations, and macro-terrain analysis. The study of DTA based on DEM is at a critical period along with the issue on whether the current GIS technology can truly support the development of geography. The research idea of geomorphology-oriented DTA is expected to be an important exploration and practice in the field of GIS.  相似文献   

基于分数阶Fourier变换的高性能SAR成像算法     

王振力  王群  陈先意  马如坡  刘晓迁 《地球信息科学学报》2020,22(11):2247-2255

传统距离多普勒算法（RD）较低精度的SAR成像质量越来越不能满足当前实际应用的需要。为解决传统距离多普勒算法成像性能低的问题,本文提出基于分数阶Fourier变换的高性能SAR成像算法（FrFT-RD）。本文详细推导SAR距离向信号运用分数阶Fourier变换时最佳阶数的计算表达式,同时给出方位向相应的计算式。理论分析表明距离（方位）向最佳阶数均取决于SAR成像参数并具有唯一性,无须迭代运算,可极大提高FrFT-RD算法的工程实用性。根据计算得到的距离向和方位向上最优阶数,在分数阶Fourier变换域完成FrFT-RD算法的构建。机载SAR模拟数据和星载SAR实测数据测试表明,FrFT-RD算法在分辨率、峰值旁瓣比（PSLR）成像性能方面比传统RD算法均得到显著提高,其中距离向和方位向分辨率提高比值分别为45.92%和48.06%;距离向PSLR和ISLR降低幅度为1.45 dB和2.59 dB,而FrFT-RD算法在方位向PSLR和ISLR成像性能方面与传统RD算法相当。  相似文献   

基于SPOT6遥感影像的滩涂湿地入侵种互花米草植株高度的反演研究   总被引：1，自引：0，他引：1       下载免费PDF全文

周在明  杨燕明  陈本清 《海洋学报》2016,38(6):1-7

本文以SPOT6 高空间分辨率遥感影像为数据源,通过植被覆盖度和地上生物量两个参数进行滩涂湿地入侵种互花米草植株高度的估算研究。结果表明,三沙湾滩涂湿地互花米草植株高度平均值为2.04 m,以1~2 m和2~3 m植株为主要分布高度,分布面积分别为6.83 km2和10.31 km2,占研究区互花米草总面积的33.83%和51.06%,小于1 m和大于3 m的互花米草仅占9.26%和5.84%。估算值与真实值之间的均方根误差为0.204,绝对误差为0.04~0.37 m。该方法是对高空间分辨率光学影像应用研究的重要尝试,其反演方法具有较好的可行性,可较为准确的获取滩涂湿地植株高度信息。  相似文献   

基于时序NDVI的昭觉植被覆盖度变化研究   总被引：1，自引：0，他引：1  

陈江玲  徐京华  李国明  王渊博  武文娟 《测绘与空间地理信息》2016,(11)

归一化植被指数(NDVI)能精确地反映植被绿度、光合作用强度,在一定程度上反映着植被的演化信息,是评价生态环境状况的重要指标之一。本文利用Landsat TM数据分别对昭觉地区2009年和2014年的NDVI进行计算,并分别利用均值法、像元二分模型及NDVI差值植被指数对研究区域植被覆盖变化进行定量分析,结果表明:昭觉县NDVI均值上升了11.6%,植被覆盖度中极度改善的面积比例约占38%,昭觉县整体NDVI植被覆盖度显著提高,并对其变化原因进行简要分析,为生态环境建设提供决策依据。  相似文献