多平台点云数据的单木参数提取精度分析

以浙江省海宁市4种代表行道树(广玉兰、无患子、悬铃木、香樟树)为研究对象,结合无人机(UAV)影像和三维激光扫描数据,利用ContextCapture、LiDAR360软件完成点云拼接、滤波、降噪和编辑,通过迭代最近点算法实现点云精细匹配,完成多平台点云数据融合,进而得到数字表面模型与数字高程模型,并制作冠层高度模型;采用分水岭分割算法对不同行道树树种的冠层高度模型进行单木分割,并综合局部最大值法实现单木树高、冠幅的参数提取。结果表明,本文方法进行行道树单木分割的精度高,树高、冠幅参数提取值的效果好,满足行道树几何参数调查要求。     

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。     

一种基于序列影像匹配的独立树冠可视化方法

介绍采用非量测相机与序列影像匹配实现独立树冠3维重建的方法。主要包括从影像提取特征点：使用多基线影像与金字塔分层相关技术进行特征点匹配;解算影像的相对方位参数;由前方交会求出各特征点的模型坐标;由模型坐标构造树冠表面三角网;由纹理映射得到树冠3维模型景观图,实现树木可视化的真3维表达。     

Errors in LiDAR-derived shrub height and crown area on sloped terrain

This study developed and tested four methods for shrub height measurements with airborne LiDAR data in a semiarid shrub-steppe in southwestern Idaho, USA. Unique to this study was the focus of sagebrush height measurements on sloped terrain. The study also developed one of the first methods towards estimating crown area of sagebrush from LiDAR. Both sagebrush height and crown area were underestimated by LiDAR. Sagebrush height was estimated to within ± 0.26-0.32 mm (two standard deviations of standard error). Crown area was underestimated by a mean of 49%. Further, hillslope had a relatively low impact on sagebrush height and crown area estimation. From a management perspective, estimation of individual shrubs over large geographic areas can be accomplished using a 0.5 m rasterized vegetation height derivative from LiDAR. While the underestimation of crown area is substantial, we suggest that this underestimation would improve with higher LiDAR point density (>4 points/m²). Further studies can estimate shrub biomass using LiDAR height and crown area derivatives.     

不同郁闭度天山云杉林林冠截留量及穿透雨量特征研究

天山云杉(Picea schrenkiana var.tianschanica(Rupr.)Chen et Fu)是构成天山山地森林生态系统的主体。选取天山森林生态系统定位研究站不同郁闭度天山云杉林作为研究对象,研究了不同郁闭度条件下天山云杉林冠截留量及穿透雨量的月变化特征、林冠截留量及穿透雨量与总降雨量间的数量关系,通过研究得出结论:林冠截留率与郁闭度表现出显著正相关关系,而穿透雨比率与郁闭度表现出显著负相关关系;穿透雨量、穿透雨比率及林冠截留量的月变化与总降雨量基本一致,林冠截留率则相反;郁闭度为0.8和0.6、0.4和0.2之间的穿透雨量无显著性差异,0.8和0.6与0.4和0.2之间差异明显,林冠截留量相邻郁闭度间均无显著性差异,而不相邻郁闭度之间均差异显著;建立了穿透雨量及林冠截留量与总降雨量间的数学关系,用以定量评价该地区天山云杉林水文生态效益。     

Influence of canopy and topographic position on soil moisture response to rainfall in a hilly catchment of Three Gorges Reservoir Area,China

Rainfall provides essential water resource for vegetation growth and acts as driving force for hydrologic process, bedrock weathering and nutrient cycle in the steep hilly catchment. But the effects of rainfall features, vegetation types, topography, and also their interactions on soil water movement and soil moisture dynamics are inadequately quantified. During the coupled wet and dry periods of the year 2018 to 2019, time-series soil moisture was monitored with 5-min interval resolution in a hilly catchment of the Three Gorges Reservoir Area in China. Three hillslopes covered with evergreen forest(EG), secondary deciduous forest mixed with shrubs(SDFS) and deforested pasture(DP) were selected, and two monitoring sites with five detected depths were established at upslope and downslope position, respectively. Several parameters expressing soil moisture response to rainfall event were evaluated, including wetting depth, cumulative rainfall amount and lag time before initial response, maximum increase of soil water storage, and transform ratio of rainwater to soil water. The results indicated that rainfall amount is the dominant rainfall variable controlling soil moisture response to rainfall event. No soil moisture response occurred when rainfall amounts was 8 mm, and all the deepest monitoring sensors detected soil moisture increase when total rainfall amounts was 30 mm. In the wet period, the cumulative rainfall amount to trigger surface soil moisture response in EG-up site was significantly higher than in other five sites. However, no significant difference in cumulative rainfall amount to trigger soil moisture response was observed among all study sites in dry period. Vegetation canopy interception reduced the transform ratio of rainwater to soil water, with a higher reduction in vegetation growth period than in other period. Also, interception of vegetation canopy resulted in a largeraccumulated rainfall amount and a longer lag time for initiating soil moisture response to rainfall. Generally, average cumulative rainfall amount for initiating soil moisture response during dry period of all sites(3.5–5.6 mm) were less than during wet period(5.7–19.7 mm). Forests captured more infiltration water compared with deforested pasture, showing the larger increments of both soil water storage for the whole soil profile and volumetric soil water content at 10 cm depth on two forest slopes. Topography dominated soil subsurface flow, proven by the evidences that less rainfall amount and less time was needed to trigger soil moisture response and also larger accumulated soil water storage increment in downslope site than in corresponding upslope site during heavy rainfall events.     

黑河流域典型生态系统的降雨截留特征——基于高时间分辨率的土壤水分数据（英文）

Rainfall interception is of great significance to the fully utilization of rainfall in water limited areas.Until now,studies on rainfall partitioning process of typical ecosystems in Heihe River Basin,one of the most important inland river basins in China,is still insufficient.In this study,six typical ecosystems were selected,namely alpine meadow,coniferous forest,mountain steppe,desert,cultivated crop,and riparian forest,in Heihe River Basin for investigation of the rainfall interception characteristics and their influencing factors,including rainfall amount,duration,and intensity,based on the gross rainfall and high temporal resolution soil moisture data obtained from 12 automatic observation sites.The results show that the average interception amount and average interception rate of the six ecosystems are significantly different: alpine meadow 6.2 mm and 45.9%,coniferous forest 7.4 mm and 69.1%,mountain steppe 3.5 mm and 37.3%,desert 3.5 mm and 57.2%,cultivated crop 4.5 mm and 69.1%,and riparian forest 2.6 mm and 66.7%,respectively.The rainfall amount,duration,and intensity all had impact on the process of rainfall interception.Among these three factors,the impact of rainfall amount was most significant.The responses of these ecosystems to the rainfall characteristics were also different.Analyzing rainfall interception with high temporal resolution soil moisture data is proved to be a feasible method and need further development in the future.     

A model to consider the spatial variability of rainfall partitioning within deciduous canopy. I. Model description

In this first paper of two, a numerical simulation model capable of simulating the spatial variability of rainfall partitioning within a canopy is presented. The second paper details how the model is parameterized, and some testing of its capabilities. The first stage of the model is to derive the mature canopy structure. This is achieved through simplified individual tree structures and a random placement routine based on a modified Poisson distribution. Following this the spatial discretization for throughfall is attained as a series of layers of triangles with a tree trunk at every apex. The number of layers is derived from the leaf area index through a modified Poisson distribution. Seasonal variation in the deciduous canopy is simulated through a time vector routine. The rainfall partitioning section of the model is based upon the Rutter model which has been modified to each individual triangle layer. The main feature of this model is that it offers a method of simulating rainfall partitioning at a scale that is a function of the size of the elementary physical components (tree and leaf scale). This can be used to investigate soil moisture variations under a canopy, or to study the variations within the forest hydrological processes themselves. © 1997 John Wiley & Sons, Ltd.     

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.     

Snow depth simulated by BATS-SAST model and its improvement

A BATS-SAST model was employed to simulate the snow processes in four snow cases of Sk_OJP 2001/2002, 2002/2003, 2003/2004 and Sk_HarvestJP 2003/2004 of Canada. At Sk_OJP site we modified the long-wave radiation and precipitation schemes. Considering the different interceptions between rain and snow and the effect of wind and canopy temperature on snow download, we improved the canopy interception model. At Sk_HarvestJP site we modified the snow cover fraction scheme. Results show that the model reasonably simulates the basic processes of snow cover. The modified model, which considers the part of the long-wave radiation and precipitation transmitted through the canopy at Sk_OJP site, can increase the simulation of snow depth which is closer to the observations. The improved canopy interception model, which influences the variation of snow depth under the canopy by changing canopy interception, is a great improvement on simulation of snow depth, especially on the ablation of snow cover. At Sk_HarvestJP site, there are obvious improvements on simulation of snow depth on the ablation of snow cover.