GPS在样地定位中的应用

就GPS（全球定位系统）单机导航样地定位的方法、精度、效率等问题进行了探讨。     

应用全球定位系统（GPS）进行样地定位

本文简单介绍了GPS概况，并根据美国、加拿大林业工作者的样定位试验，说明了用差分法样地定位在10米之内，用自动选择连续测定和加处理（不用差分法）的方法误差为20米之内，不用后处理的其它直接测定方法误差在30米以上，林冠对GPS接受卫星信号有影响，用GPS样地定位比传统方法样地定位效率高，无样地定位经验的新手用GPS定位受益大。     

GPS接收机在林业中的综合应用

GPS技术在林业系统中的大量应用,是从上世纪末开始的,其主要的应用范围包括：面积测量、样地定位、护林防火、飞播导航、林权界定、伐区划定、造林验收以及病虫害防治等方面,笔者在此谈谈GPS接收机在林业中的应用。     

GPS在造林工程中的应用

GPS（Global Positioning System,全球定位系统）是一种确定地面点位置信息的技术系统.其主要功能是导航和定位.在造林规划设计外业调查中,传统的导航和定位的工具是纸质地图、罗盘仪和海拔仪,而现在和将来的外业调查定位工具完全可以由电子地图（或高分辨率的遥感图像）和GPS代替.其原因就是利用GPS接收机可随时获得地面点的地理坐标（定位信息）,又可以获得地面点之间的方位角和距离（导航信息）;利用地面的电子地图（或遥感图像）可以获得调查区域的宏观位置信息.目前,在造林规划设计实践中,应用地形图配合GPS进行外业调查的方法将越来越普及.但是,由于林业生产单位的技术条件相对落后,技术人员的专业知识比较差,使得这种方法的广泛应用受到很大的阻力,因此,大力普及GPS基本知识和应用方法,在当前林业生态工程建设中具有十分重要的意义.本论文主要以SP24型手持GPS为例,对其在造林规划设计的应用方法进行探讨,供林业技术人员参考.     

GPS手持机定位校正参数的计算及设置

当采用GPS进行定位、导航时、用户所设坐标系统及所在地区不同，校正参数也应不同；正确的参数设置是精确定位、导航的基础与关键；林业中“连清”样点的定位、导航，各种境界线测量，森林火灾位置确定等在使用GPS时，均需输入正确的校正参数；为此，文中讨论了有关参数的计算与设置。     

四旁树清查的新方法

利用“连清”部分样地作为固定监测体系，采用分层两阶抽样的调查方法，利用地球定位系统(GPS)定位、导航的功能，清查了我省的四旁树资源。与传统方法相比，节省调查经费80％，提高工作效率10倍以上。     

GPS在云南"连清"复查工作中的应用效益分析

从不同角度分析了以GPS定位技术为手段，提高森林资源“连清”样地调查工效和定位精度，通过对坐标的转换，实现了图面样点与地面样地的匹配。在2002年云南“连清”第四次复查工作中，全面使用GPS并获得成功，为在森林资源连续清查推广应用GPS技术提供了宝贵的实践经验。     

应用全球定位系统(GPS)进行样地定位

本文简单介绍了GPS概况,并根据美国、加拿大林业工作者的样地定位试验,说明了用差分法样地定位误差在10米之内。用自动选择连续测定加后处理(不用差分法)的方法误差在20米之内。不用后处理的其它直接测定方法误差在30米以上。林冠对GPS接受卫星信号有影响。用GPS样地定位比传统方法样地定位效率高。无样地定位经验的新手用GPS定位受益大。     

手持式Garmin、UniStrong GPS仪点位数据的批量导入方法

在森林资源连续清查和森林资源规划设计调查及点位数据定位测量工作中,一般用手工将样地点坐标逐个输入到手持式GPS仪中,该方法不但效率低,且容易出错。通过实践,利用Mapsource、Mapsource助手、Unistrong GIS Office等软件,将点位数据文件生成MapSource数据交换格式GPX文件,直接导入Garmin、UniStrong GPS仪,实现了快速高效地向手持Garmin、UniStrong GPS仪中批量输入样地点数据的目标。该方法不需要将样地点坐标逐个输入和编程,实用性强,极大地提高了工作效率。     

手持GPS在森林防火中的应用

从手持GPS的定位、导航、测面积等功能方面,阐述了GPS在森林火灾蔓延过程中火头的快速定位、火因调查中起火点的定位及如何利用GPS辅助火场逃生、组织扑火队伍撤离火场、测定火烧迹地面积。同时,对GPS的参数设置、选择适合森林防火工作的机型等做予以说明。     

利用GPS技术对森林资源连清样地定位的研究

简要介绍GPS技术及其在森林资源连清样地定位试验中的使用情况，指出了引入GPS技术对森林资源连清样地的定位是可行的，提出了存在的问题及解决途径。     

Stand parameter extraction based on video point cloud data

Monitoring sample plots is important for the sustainable management of forest ecosystems.Acquiring resource data in the field is labor-intensive,time-consuming and expensive.With the rapid development of hardware technology and photogrammetry,forest researchers have turned two-dimensional images into three-dimensional point clouds to obtain resource information.This paper presents a method of sample plot analysis using two charge-coupled device(CCD) cameras based on video photography.A handheld CCD camera was used to shoot the sample plot by surrounding a central tree.Video-based point clouds were used to detect and model individual tree trunks in the sample plots and the DBH of each was estimated.The experimental results were compared with field measurement data.The results show that the relative root mean squared error(rRMSE) of the DBH estimates of individual trees was 2.1-5.7%,acceptable for practical applications in traditional forest inventories.The rRMSE of height estimates was2.7-36.3%.Average DBH and heights,and tree density and volume were calculated.Video-based methods require compact observation instruments,involve low costs during field investigations,acquire data with high efficiency,and point cloud data can be processed automatically.Furthermore,this method can directly extract information on the relative position of trees,which is important to show distribution visually and provides a basis for researchers to regulate stand density.Additionally,video photography with its unique advantages is a technology warranting future attention for forest inventories and ecological construction.     

结合自适应阈值与峰值的LiDAR林分平均高反演方法研究

随着激光雷达获取的点云密度不断增加,提取样地尺度的林分平均高成为可能。但样地尺度林分平均高的提取精度与树种之间的关系尚不明确,急需一种能适应各种树种的林分平均高提取方法。以广西国有高峰林场为例,采用机载LiDAR点云数据生成的冠层高度模型(Canopy height model,CHM),结合地面实测的201个样地数据,提出了一种结合自适应阈值与峰值的林分平均高提取算法,并分析了树种对提取精度的影响。结果表明:1)不同树种的林分平均高提取精度存在差异,杉木精度最高,而桉树和其他阔叶树种精度次之;2)自适应阈值结合峰值的算法能够较好提取林分平均高(R²=0.75,RMSE=3.11m,rRMSE=22.07%),并且对于不同的树种都有较强的稳健性;3)阔叶树种和针叶树种对不同的提取方法存在敏感性差异。研究提取的林分平均高可为森林蓄积量与生物量反演研究提供依据和参考。     

Estimating forest characteristics in scanned aerial photographs with respect to requirements for economic forest management planning

The objective of forest management planning is often expressed as maximum sustainable economic yield. Methods used to collect information for forestry planning should, therefore, include variables significant for economic evaluations of management alternatives. It is important to be able to differentiate mature stands with respect to timber volumes and species mixture. In this study, digital high‐altitude aerial photographs are tested as a data source for planning. Circular plot data from a forest estate in northern Sweden were used as reference material. Global positioning system (GPS) measurements, with differential correction, were used to georeference the plots. Harvesting priorities were calculated for each plot using the Forest Management Planning Package. Volumes, species mixture and harvest priorities were estimated using regression analysis based on textural and spectral information from aerial photographs. The results show that the dependent variables could be estimated fairly well using only spectral information, e.g., R ² = 0.44 when estimating timber volume at reference plot (10 m radius) level. Aggregated to stand level, the precision was comparable with customary field survey methods (e.g., RMSE= 13.4% for timber volume).     

掌上电脑在"二类调查"中的具体应用

从电子地图的应用、加载卫星图像、GPS导航、样地检尺、属性数据录入、属性数据的查询和统计以及数据的导入和导出几个方面,详细介绍了应用"3S"技术开发的掌上电脑应用系统在"二类调查"中的具体应用过程.     

Designing fecal pellet surveys for snowshoe hares

Index methods can be valuable for monitoring forest-dwelling vertebrates over broad spatial or temporal scales. Fecal pellet counts are often used as an index of density or habitat use of snowshoe hares, Lepus americanus, but previous surveys have used different plot types and sample sizes, leading to problems comparing results from different studies and questions about the inferential power of each study. In this paper, we use field data and simulations to examine how the precision, bias, and efficiency of four commonly used plot types vary with plot type, pellet density, and sample size. Although no one plot type was consistently superior, we recommend thin rectangles (5.08 cm × 305 cm (2 in. × 10 ft), 0.155 m²) or 1 m² circles over 0.155 m² circles or 10 cm × 10 m (1 m²) rectangles. We recommend that researchers explicitly address the power of their survey design to detect different pellet densities, because much larger sample sizes are needed at low pellet densities than at high pellet densities to obtain similar precision. Small sample sizes are also much more likely to be biased, which could lead to incorrect inferences about management of snowshoe hare populations. Both uncleared and cleared plots performed well and will have value in different research contexts.     

广西森林资源连续清查角规样地体系评价

广西森林资源连续清查(以下简称"广西连清)"角规样地体系,是我国唯一的以点抽样理论为基础,以固定角规样地为监测载体的省(区)级森林资源连续清查体系。广西连清第7次复查,除了增设的方形样地调查以外,还对原有的角规样地进行了复查,因此本文得以用同时进行调查的方形样地调查结果作为参照对象,对角规样地体系的优点和存在的问题进行定性和定量相结合的综合分析评价。分析评价结果表明,与方形样地比较,角规样地除了具有显著的隐蔽性外,外业工作量只相当于方形样地的53%,两套体系的活立木蓄积量差异仅为3.16%,角规样地和方形样地体系总蓄积量抽样精度分别为94.47%与94.57%,均达到国家森林资源连续清查技术规定要求(≥90%)。角规样地复位率大于规定的98%,样木复位率远大于规定的95%,达97%以上,能满足林木蓄积生长量和消耗量监测的要求。角规样地体系的不足主要是由于漏测木和进测木的存在,导致森林资源的现状估计值偏低,且动态估计精度明显低于方形样地体系。     

A simulation study on the effects of plot size and shape on sampling plant species composition for biodiversity management

Sustainable management of plant diversity in a forest requires adequate information that is often derived from samples. With limited resources, the plot design has to be efficient. Most studies focused on evaluating effects of plot designs on sample estimates of species richness at landscape scale. This study aims at filling a knowledge gap by investigating how plot size and shape affect sample estimates of species composition at a local scale. Two census datasets with distinct forest ecosystems were used. Fifteen combinations of plot size and shape were simulated. Species compositional similarity between two combinations of plot design at a sample point was estimated by Jaccard and Sørensen indices, and their abundance-adjusted counterparts. Similarity in species composition decreased with increasing difference between two plot sizes. Plots with varying shapes were found to have different local species composition but could be similar in the number of observed species, which has not been explicitly reported elsewhere. For less species-rich forests, a 0.025–0.05 ha circular plot is recommended. For species-rich forests, a 0.05–0.1 ha rectangular plot with aspect ratio of at least 1:20 is recommended. The results should be of interest to stakeholders managing small area forests for conservation of plant diversity.