Estimation of GPS positional accuracy under different forest conditions using signal interruption probability

We proposed a signal interruption probability (SIP) value indicating the frequency of global positioning system (GPS) signal interruption or the fragmentation of GPS data, and used it to estimate the success probability of ambiguity resolution in carrier-phase differential GPS (DGPS) as well as the horizontal precision of code-phase DGPS under different forest conditions. In field tests, a rover was set up at four observation points, each representing a different condition within a forest. At each observation point, static surveying was conducted for four periods of 30 min, and data from the first 1, 5, 15, and 30 min from each observation point were extracted for analysis. The position of each point was calculated by baseline analysis using three types of GPS data, i.e., dual-frequency (L1 and L2), single-frequency (L1), and code-phase DGPS data. The results showed that ambiguity resolution was a key factor in determining the horizontal accuracy of carrier-phase DGPS, and that the success probability of ambiguity resolution differed greatly according to forest conditions, which were well explained not by the index of the canopy opening but by the SIP. Furthermore, estimation of the success probability of ambiguity resolution was made based on the SIP and the observation period using a logistic regression model. The horizontal precision of code-phase DGPS was also estimated based on the SIP and the observation period. In conclusion, the SIP was found to be an effective indicator of GPS positional accuracy under different forest conditions.     

Positioning precision and sampling number of DGPS under forest canopies

 Experimental results were studied to determine the relationships between positioning precision of a differential global positioning system (DGPS) and forest type, antenna height, and season, and to clarify the relationship between sampling number and the convergence of positioning precision. Observation was carried out for 24 h. Mean circular area probability (CEP₉₅) was 2.80 m for deciduous broadleaved trees, and 4.99 m for conifers. The mean CEP₉₅ taken at 7 m height (3.14 m) was higher than that at 1 m height (3.92 m) at all sites. The mean CEP₉₅ taken during the defoliation season (2.65 m) was slightly better than during the foliation season (2.96 m). There were significant differences between forest types (P < 0.001) and antenna heights (P < 0.05). Positioning precision was not noticeably improved if the sampling number was around ten or less. A sampling number of 100–1000 or more is required before substantial improvements can be expected. As long as high positioning precision is not required, it is acceptable to use 2D & 3D modes and relatively few samples to take measurements. Received: April 24, 2002 / Accepted: October 10, 2002 Correspondence to:I. Sawaguchi     

Accuracy, precision, and reliability of chemical measurements in natural products research

Natural products chemistry is the discipline that lies at the heart of modern pharmacognosy. The field encompasses qualitative and quantitative analytical tools that range from spectroscopy and spectrometry to chromatography. Among other things, modern research on crude botanicals is engaged in the discovery of the phytochemical constituents necessary for therapeutic efficacy, including the synergistic effects of components of complex mixtures in the botanical matrix. In the phytomedicine field, these botanicals and their contained mixtures are considered the active pharmaceutical ingredient (API), and pharmacognosists are increasingly called upon to supplement their molecular discovery work by assisting in the development and utilization of analytical tools for assessing the quality and safety of these products. Unlike single-chemical entity APIs, botanical raw materials and their derived products are highly variable because their chemistry and morphology depend on the genotypic and phenotypic variation, geographical origin and weather exposure, harvesting practices, and processing conditions of the source material. Unless controlled, this inherent variability in the raw material stream can result in inconsistent finished products that are under-potent, over-potent, and/or contaminated. Over the decades, natural product chemists have routinely developed quantitative analytical methods for phytochemicals of interest. Quantitative methods for the determination of product quality bear the weight of regulatory scrutiny. These methods must be accurate, precise, and reproducible. Accordingly, this review discusses the principles of accuracy (relationship between experimental and true value), precision (distribution of data values), and reliability in the quantitation of phytochemicals in natural products.     

Application of dual-frequency GPS receivers for static surveying under tree canopies

 The objectives of this study are to evaluate the accuracy of dual-frequency GPS receivers in static surveying in forests and to develop a model to estimate the probability of resolving ambiguity by logistic regressions, with independent variables being the observation period length and an index of canopy opening. In this study, a rover receiver was set up at four points in the forest (at a treeless point, under a large canopy gap, under a small canopy gap, and under closed canopies), and static surveys were conducted for 4 h at each point. The observed data were post-processed with the data from the base station, and the baseline data were repeatedly post-processed while changing the length of the observation periods. As a result, positional accuracies were decreased more under tree canopies than at the treeless point, but under tree canopies several integer ambiguities were resolved within 15 min by using a dual-frequency GPS receiver. The result also showed that ambiguity-fixed solutions using a dual-frequency GPS receiver produced the most accurate positional data under tree canopies. Moreover, the probability of resolving ambiguity was estimated by logistic regression with the independent variables being the index of canopy opening and observation period lengths. Received: July 6, 2001 / Accepted: October 25, 2002 Acknowledgments This study was supported in part by a Grant-in-Aid for Scientific Research from the Japan Ministry of Education, Culture, Sports, Science and Technology (No. 12760104). We would like to express our gratitude to Mr. Masayuki Uchiyama and Mr. Yoshito Fujita (Akasaka Tec Inc.) for their experimental support and valuable advice on GPS positioning. Correspondence to:H. Hasegawa     

基于手持式GPS接受机的林区坐标差分研究

本文研究我国林业应用较多的手持式GPS接收机用手坐标差的原理、技术和方法。文章建立了基于基准站两个历元之间的直线内插模型和三个历元的抛线内插模型 ,并编制相应的VB计算程序 ,通过麦哲伦GPS2 0 0实测验证 :对于 9874 5 4 1m2 地林面积 ,采用GPS单机定位 ,其相对误差为 19 0 0 % ,而采用直线内插、抛物线内插法差分定位其面积误差为 3 0 0 %和 1 91% ,其实测定精度为 :单机± 4 9m ,直线内插差分法±3 0m ;抛物线内插法差分± 2 8m。     

Effects of polyline simplification of dynamic GPS data under forest canopy on area and perimeter estimations

The objectives of this study were to determine Global Positioning System (GPS) positional errors while moving under the forest canopy and to clarify the effects of polyline simplification on area and perimeter estimations. We used the Pathfinder Pro XR and GPSMAP 76S, which are categorized as “high-end mapping” and “general navigation” GPS receivers, respectively. The field tests were conducted in both natural and plantation forests. The results showed that the Pathfinder Pro XR, which has better multipath rejection technology, worked well, especially in the plantation forest under unfavorable conditions of higher stand density. We used analysis of variance to clarify the effects of the receiver type, positioning mode, stand type, and polyline simplification method on area and perimeter estimations. The receiver type and positioning mode were found to be significant factors that affected area estimation. The Pathfinder Pro XR estimated the area more accurately than the GPSMAP 76S, and differential GPS estimated the area more accurately than autonomous GPS. With respect to the perimeter, the receiver type, positioning mode, and polyline simplification method were found to be significant factors. The results showed that perimeter estimation was improved by using the velocity filter, and further improved by using the velocity filter and Douglas-Peucker algorithm, especially when the Pathfinder Pro XR was used. The GPSMAP 76S estimated the perimeter accurately without any filtering because its default speed filter worked well, even though the GPSMAP 76S is a general navigation GPS receiver.     

手持型GPS接收机面积测量精度研究

在理论分析手持型GPS接收机面积测量原理的基础上,对9个不同大小地块在不同时段、不同干扰条件下实际面积测量的精度进行分析,详细论证了手持型GPS接收机完全能够满足退耕还林、造林地验收、小班面积测量等精度的需要,可广泛应用于森林资源调查.     

全球定位系统(GPS)的林区作业方案研究

全球定位系统(GPS)在林业中已经得到了广泛的应用,但如何确定切实可行的作业方案还有待研究。在福建永安市进行的GPS测量试验,分别针对林区地物进行了不同方式的测量,对其测量精度进行了比较和评价。提出了一种差分测量中测量区缺少基站点的解决方法,对不同的林业作业采用的GPS测量方案进行了探讨。     

基于GPS RTK技术植树造字定位放样的应用实践

在"绿色双牌"植树造字定位放样项目中,先利用RTK进行1/500数字地形图测绘,在数字化成图软件CASS5.1平台上生成等高线,并进行字体整体布局设计,提取放样坐标和放样高程等放样数据,生成放样坐标数据文件,再利用RTK的坐标放样功能程序放样"绿色双牌"字体轮廓线上特征点坐标。与传统的"光学法"放样相比,RTK进行数字地形图测绘和施工放样具有明显的优势,主要表现使用方便、精度高、减少测量标志建设费用、不受通视条件限制等方面。通过实践,总结了RTK进行数字地形图测绘和施工放样以及植树造字定位放样的体会和经验。     

基于VRS技术的DGPS-PDA在森林资源连续清查中的应用研究

在介绍GPS、DGPS、RTK、VRS、PDA等技术的基础上,详细阐述了基于VRS技术的DGPS．PDA在森林资源连续清查中应用的工作流程及操作步骤。研究表明,定位平均精度可达0．5m左右,在信号较好的地方,精度可达0．3m左右,提高了样地定位精度和连清工作的连续可比性。利用PDA进行野外数据采集,提高了工作效率,可实现森林资源连续清查的无纸化。     

GPS与罗盘测量在林业调查设计中的应用比较

2002年6月至2006年6月,在林业调查设计中,采用GPS与罗盘两种测量方法,得到了304个地块的面积及3 900多个线段的长度。结果表明,面积越大,线段越长,两种测量方法之间的误差越小。当面积大于3.34 hm2,距离大于50 m时,误差范围小于5%,完全可以达到林业资源调查设计要求的标准。因此,作者认为,使用GPS可以代替罗盘测量。     

Environmental management and sustainable development in forested mountain areas of northeast China

IntroductionItiswellknownthatChinahasalonghistoryandcivilization,alargepopulationandlesscultivatedland.Thiskindofsituationisrelevanttotheresourcesdepletionandrecurrentnaturaldisasters.ForestsareveryimportantbothfortheeconomicalconstructionandfortheenvironmentalproteCtion.ThegraveinundationthatoccurredatsouthandnortheastriversintheSummerof1998givesusabitterlesson,manyscientistsandmassesbelievethatthelongandoverforestCuttingshouldberesponsibleforthecatastrophe.Theforestsonthemiddleandupperreac…     

基于DGPS的SPOT5遥感影像几何精校正研究

采用DGPS系统中的载波相位差分技术均匀地选取地面控制点,利用ERDAS IMAGINE9.1遥感影像处理软件,对天桥岭林业局太阳林场的SPOT5遥感影像进行了几何精校正。结果表明：采用3次多项式校正,相应面积控制点个数比在0.06～0.09（个.km-2）之间时校正精度最高,校正后误差为0.603个像元,即1.508 m。此方法不仅可以满足林业作业的精度要求,还可使外业工作量最小。     

手持GPS林地测绘自动空间定位成图系统的开发研究

运用加拿大林业GIS和GPS的先进技术平台，结合林区工作的需要，开发研制了CLP5．0系统，该系统具有GPS手持机林业专题图自动空间定位、自动按比例尺打印输出带地理要素和林业信息的成图功能。     

基于GPS和AUTOCAD技术在林权证附图上的应用

文章在实践中利用GPS(卫星定位系统)采集林地的野外数据,应用AUTOCAD软件对所采集的定位数据进行处理,形成林地图形,测算林地实际面积,为林权证附图绘制提供了技术保障。     

eTrex GPS接收机在森林资源调查中的定位精度评估

针对GPS在森林资源调查中的应用现状,主要阐述了手持式GPS接收机的定位精度,并以山东中部的徂徕山林场作为实验区,研究了eTrex手持式GPS接收机和Z-MAX差分GPS接收机观测值的变化规律。     

GPS在导航定位中出现系统误差的原因及纠正方法

近几年,我国引进了美国全球卫星定位系统,并在各个领域广泛应用。它的使用为工程地质、野外调查的现地定位和测距提供了极大的方便和一定精确性,但同时也伴随着误差的存在。出现误差的原因是多方面的,如GPS本身的误差,GPS与参照地形图不匹配所产生的误差。GPS的星历是以WGS84坐标系为依据建立的,而我国现在所使用的地形图是依据北京54坐标系统建立的。由于我们使用了不相匹配的两种工具去进行现地定位测距或导航,必将会产生一定数量的系统误差,以致在野外做定位或导航时,满足不了测量的精度要求。由于林业野外调查工作存在着地域辽阔、跨地区、跨时区、跨六度带,及地形地势的大幅度起伏和时间的不确定性,所以不可能按照GPS说明书上的说明,去进行精确的理论计算和当地三角点、水准点等明显地物点坐标参数的收集。如何找到一个即能达到一定精度要求,又简单易行的系统纠偏方法,成为野外测量工作必须解决的当务之急。     

GPS技术的现状及在林业中的应用前景

本文概述了GPS技术目前的发展状况，总结了GPS在林业工作中正在应用的情况，最后，对GPS在林业中的发展前景进行了探讨。     

Google Earth和GPS在林业司法鉴定中的应用

涉林案件中,常见现场地表被剥离,而林业司法鉴定中需要确定被毁坏林地类型及面积.Google Earth影像往往是若干年前的卫星影像,保留着未破坏前的现场影像,故可利用手持GPS机定位现场边界,根据地理坐标准确定位出Goosle Earth影像,利用StitchMaps软件下栽保存,在GIS软件中,勾绘各地类边界、测算面...     

手持GPS与ArcGis结合在基层农林业面积调查中的应用

使用佳明(GARMIN)eTrex30(小博士)手持导航型GPS接收机沿调查地块边界绕测自动采集航迹并储存,在ArcMap中通过航迹数据格式转换、投影变换、创建调查地块面要素等操作,能实现地块面积等计算和空间位置成图.结果表明,GPS和ArcGis结合能完成特殊情况下使用图纸勾绘难以完成的面积等调查工作,调查精度高,成图方便.