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     

飞机播种造林中的GPSMAS导航技术及其定位精度

GPSMAS结合了GPS和G IS技术,通过编写程序实现对GPS卫星定位数据的接收、传输和处理,把当前定位数据适时转化为可视图像,具有准确高效的图示导航功能。GPSMAS导航定位的精度取决于GPS接收机定位精度和播区设计测点精度。其所达精度完全能满足飞机播种造林(种草)导航的需求。     

全球定位系统(GPS)与林业工程

用户利用ＧＰＳ接收机、计算机及通信设备可以对静止及移动目标进行三维定位及实时跟踪。同其它定位方法相比，ＧＰＳ具有全天候、实时连续、精度高等优良性能且价格低廉。目前，美国、加拿大及瑞典等国已将ＧＰＳ技术应用于林业工程之中。本文概述了ＧＰＳ的基本工作原理、算法、系统构成和应用状况，以及ＧＰＳ在林业资源管理及工程上的应用前景。     

GPS卫星星历插值拟合方法研究

利用GPS进行定位,卫星星历的精度将直接影响到地面接收机的定位精度。对GPS卫星星历的Lagrange插值、Neville插值以及最小二乘法拟合方法进行比较分析,确定3种算法的卫星位置计算精度,探讨多项式阶数和时间间隔的合理选择等问题,为进一步研究卫星星历提供依据。     

林区地形条件对GPS定位精度的影响

在林区周边多种地形中布设试验点,通过实地测量,探讨地形因子对高性能GPS接收机单点定位和GPS-RTK定位精度的影响。研究表明:两种常用的GPS测量方式同一时间段观测值有一定的聚集性,不同时段之间会产生整体性偏差;Trimble 5800 GPS接收机单点定位在不同地形中测量的内外符合精度为0.512~4.465 m,受山体和建筑物的影响较大,较空旷区域中可以达到分米级精度;RTK技术在观测条件较好时,平面中误差大多在1 cm以内,高程中误差为1~3 cm,上午、下午两个时段定位精度相近,在郁闭度较高的林中观测精度较低,只有亚米级,高程精度更低,大多历元得不到固定解,在山谷等更恶劣的地形中,甚至得不到浮动解。     

Comparing the precision and accuracy of GPS positioning in forested areas

The objective of this study is to clarify the performance of the Global Positioning System (GPS) in forested areas after selective availability (SA) was turned off. In this study, we conducted a field test on horizontal and vertical positional errors of GPS positioning at different points in forested areas. The precision and accuracy of GPS positioning at different points were then calculated and compared. Furthermore, the effect of differential GPS (DGPS) on precision and accuracy was analyzed using analysis of variance (ANOVA), and the necessity for DGPS after SA was turned off was discussed. As a result, the largest horizontal precision errors were found to be in the plantation forest, followed by the natural forest and forest road. On the other hand, precision errors were smallest at the landing, around which there were no obstacles. Horizontal accuracy errors were greatly improved by using the DGPS. Large vertical precision errors were produced in the plantation forest, on the forest road, and in the natural forest, while those at the landing were much smaller. Vertical accuracy errors were also relatively small at the landing. In conclusion, tree canopies greatly affected precision errors, and the DGPS improved not horizontal precision but horizontal accuracy. The autonomous GPS is sufficiently useful for purposes in which horizontal positional errors of a maximum of 10m are allowable. However, the DGPS should be used for surveying and mapping, for which higher accuracy is necessary.     

南湾国家级森林公园森林景观斑块特征分析

根据土地类型和植被特征划分景观类型,然后运用GIS软件进行数字化,并计算斑块指标。分析结果表明:南湾国家级森林公园森林景观共有松林、杉林、栎林、竹林、板栗林和茶园等6种类型。各类型的面积、周长及斑块数都不均衡;松、杉林景观处于主导地位;茶园形状最复杂,而松、杉林景观破碎化程度最高,受人为因素影响最大。     

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。     

Species richness in sugi (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. DON) plantations in southeastern Kyushu,Japan: the effects of stand type and age on understory trees and shrubs

 The species richness of trees, shrubs and climbing plants was investigated in 41 sugi (Cryptomeria japonica D. Don) plantations of different stand age and area in southern Kyushu, southwestern Japan. Altogether 174 species were found, of which 145 infrequent species were selected for analysis. Two groups were extracted from the species list according to their occurrence in older (49 spp.) or younger (28 spp.) stands, the latter containing a higher percentage of climbing plants and species with wind-dispersed seeds. In contrast, the older stand group contained major tree components typical of seminatural, evergreen broadleaved forests in the region and was more heavily dependent on stand age, especially for species with gravity- and frugivore-dispersed seeds, showing a gradual increase up to 60 years old. The species richness was less correlated with edge perimeter facing seminatural forests and the years after latest thinning. The juxtaposition of plantation compartments with stands of seminatural forest or other plantations, as well as the compartment's origin as former plantation site or a seminatural stand, had relatively little influence on species richness. However, topographic variation was important in determining the species composition, with valley stands having higher species richness and containing many plants typical of the regional seminatural forests. These results suggest that (1) the major trend of species richness is determined by the presence of old stand type species, (2) topographic variation of species richness remains even after establishment of plantations, and (3) the normal rotation period of sugi plantations (35–40 years) may therefore be too short to conserve the maximum potential species diversity within the working forest. Received: June 4, 2001 / Accepted: August 26, 2002 Acknowledgments We wish to thank the staff of the Miyazaki University Forests for cooperation in the fieldwork. A part of this study was supported by the Grant-in-Aid for Scientific Study from the Ministry of Education, Science and Culture of Japan (no. 09041071 and no. 10460068). Correspondence to:S. Ito     

3S技术在延平区森林资源管理中的应用

简述了地理信息系统(GIS)、遥感技术(RS)、全球定位系统(GPS)的概念和特点,介绍了3S技术在森林资源管理中的应用现状,旨在促进延平区的林业科技发展。     

基于GIS大连河口湾植被现状调查报告

以"3S"技术(RS、GlS、GPS)作为技术支撑,以生态学和景观生态学作为理论基础,通过分析研究规划区的植被覆盖度现状,为规划该区决策者提供强有力的基础植被信息资料。     

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.     

手持GPS在森林公园规划中的应用研究

简要介绍了GPS定位系统的概况，针对手持GPS 315的性能，根据森林公园规划中的特点，在固定景点定位、面积测定、路线导航、直线测距等方面进行试验。结果表明，手持GPS 315在森林公园规划、旅游资源调查等方面有广阔的应用前景。     

Mapping the effect of spatial and temporal variation in climate and soils on Eucalyptus plantation production with 3-PG,a process-based growth model

In the wet tropics, near the Atlantic Coast of Brazil, drought may reduce plantation yields by as much one-third over a six-to-seven-year rotation. For land owners, annual variation in production cannot be estimated with empirical models. In this paper, we examine whether the process-based growth model, 3-PG is sufficiently sensitive to climatic variation to provide a virtual record of changes in growing stock across 180,000 ha eucalypt plantation estate. We first mapped variation in climate and soil properties, and then ran simulations for the current planted forest with ages varying from one to seven years. Model predictions of stand volume and mean tree diameter agreed closely with measurements acquired on 60 reference plots monitored over the test period; the prediction of mean annual increment (MAI) was less reliable. Available soil water (ASW) and leaf area index (LAI) were also measured and compared with the model estimations. Vapour pressure deficit (VPD) and ASW accounted for most of the variation in yields. We conclude that this spatial modelling approach offers a reasonable alternative to extensive ground surveys, particularly when climatic variation extends beyond the historical average for a region.     

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.     

Reliability of GPS/GNSS-based positioning in a forestry environment

The critical environment is one of the main insufficient to positioning. Geodetic observing systems such as the global positioning system (GPS) and the global navigation satellite systems (GNSS) are routinely used to estimate the contaminating effects by critical environment. In an effort to define the accuracy and reliability of GPS/GNSS positioning, we investigated the data having contaminating effects due to forestry environment. Some reliability criteria and geometric concepts were defined and then examined by them. Two sets of data were collected in open sky and closed canopy separately. The analysis of the observed data was performed using the reliability criteria and geometric concepts. The accuracy and reliability of positioning strongly depended on the canopy ratio and satellite availability. The minimum detectable error on baseline was estimated about 2.5 mm under closed canopy. The number of observable satellites and minimal detectable errors were computed for each epoch. The minimal biases on estimated baselines, bias-to-noise ratios for estimating baseline components and probability of success of the integer ambiguity solution were defined in case of forest canopy. Finally, geometric quality could be achieved using the factors of dilution of precision. Thus, the presented accuracy and reliability concepts fulfill the requirement proposed by the global geodetic observing system in forest environment.     

Attitudes of small-scale forest owners to their properties in an ageing society: Findings of survey in Yamaguchi prefecture, Japan

Populations of most developed countries have been ageing, and the populations of Japanese mountain villages are estimated to have reached into a super-ageing society. In particular, because forestry is unprofitable and due to the economic recession in Japan, many small-scale forest owners face the problems of ageing. For policy-makers, it is important to assess the socioeconomic impacts of forest owners’ ageing in order to ensure the sustainable management of forests. A survey was conducted of forest owners in Yamaguchi Prefecture, which is famous for overall depopulation and ageing of the rural population. It was found that 83% of 687 plantation forest owners who responded in the survey were 60 years or older and 76% did not have forestry income over the past three years, but 81% had kept up ownership of their forest as the traditional family property. In terms of forest management intentions, the respondents were found to consist of four types, namely ‘family management’, ‘commissioned management’, ‘de-accession’ and ‘possession without proper management’. Differences in evaluations of hypothetical policies were found among the four types.     

思茅松人工林的高效经营模式及其效益分析

介绍了以产脂为定向培育目的的思茅松人工林高效经营模式,并对其经济、生态和社会效益进行了分析。此高效经营模式的根本在于定向培育思茅松采脂原料林,使其经济效益最大化。预计该模式22年经营期的累计纯收入可达37429.5元/hm2,远远高于思茅松用材林。     

Assessing Point Accuracy of DGPS Under Forest Canopy Before Data Acquisition,in the Field and After Postprocessing

A low-cost, hand-held, 10-channel, single-frequency Global Positioning System (GPS) receiver observing pseudorange and carrier phase was used to determine the positional accuracy of 35 points under tree canopies. The mean position error based on differential postprocessing ranged from 0.49 to 3.60 m for 2-20 min of observation at points with basal area <30 m 2 ha -1 . For points with basal area S 45 m 2 ha -1 the mean position error ranged from 2.15 to 5.60 m. Regression analysis revealed that basal area and observation period were the most significant factors to predict the position error that could be obtained by GPS data collection before or during data acquisition ( R 2 = 0.37). After differential postprocessing, the most significant factors to predict position error were the standard deviation reported by the postprocessing software and whether both pseudorange and carrier phase were used to compute the coordinates or pseudorange only ( R 2 = 0.57). The position error decreased with decreasing density of forest, increasing length of observation period, decreasing standard deviation, and combined use of pseudorange and carrier phase.     

A projected increase in stand volume of introduced provenances of Acacia mangium in seedling seed orchards in South Sumatra, Indonesia

 Increases in stand volume with some currently introduced provenances of Acacia mangium: Papua New Guinea (PNG) and Far North Queensland (FNQ), were projected based on their superiorities in 3-year height growth in seedling seed orchards using the growth model developed for unthinned plantation for pulp and paper production in South Sumatra, Indonesia. The height growth of these provenances was better than that of the local selections from Subanjeriji by 10%–15% at 3 years old and these percentage superiorities would be expected to remain at around 9%–14% until the 8-year rotation. This amount of increase would result in a 7%–10% increase in basal area and hence it would produce a 17%–26% increase in stand volume at rotation age when compared with the Subanjeriji seed source that was being widely used for the plantation establishment of A. mangium in Indonesia. Received: July 24, 2002 / Accepted: December 3, 2002 Acknowledgments The authors thank Mr. Hardjono, the director of plantation establishment at PT Musi Hutan Persada for his permission to use data of permanent plots for the growth modeling of A. mangium. The authors are grateful to the staff at PT Musi Hutan Persada, Research and Development Center for Biotechnology and Forest Tree Improvement, Japan International Cooperation Agency for their implementations of the study. Our thanks are also due to Dr. Yoshida, associate professor at Kyushu University, for his advice on developing the growth modeling work. Correspondence to:S. Kurinobu