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121.
Remotely sensed estimation of forest canopy density: A comparison of the performance of four methods
Chudamani Joshi Jan De Leeuw Andrew K. Skidmore Iris C. van Duren Henk van Oosten 《International Journal of Applied Earth Observation and Geoinformation》2006
In recent years, a number of alternative methods have been proposed to predict forest canopy density from remotely sensed data. To date, however, it remains difficult to decide which method to use, since their relative performance has never been evaluated. In this study the performance of: (1) an artificial neural network, (2) a multiple linear regression, (3) the forest canopy density mapper and (4) a maximum likelihood classification method was compared for prediction of forest canopy density using a Landsat ETM+ image. Comparison of confusion matrices revealed that the regression model performed significantly worse than the three other methods. These results were based on a z-test for comparison of weighted kappa statistics, which is an appropriate statistic for analysis of ranked categories. About 89% of the variance of the observed canopy density was explained by the artificial neural networks, which outperformed the other three methods in this respect. Moreover, the artificial neural networks gave an unbiased prediction, while other methods systematically under or over predicted forest canopy density. The choice of biased method could have a high impact on canopy density inventories. 相似文献
122.
Nicola Perfetti 《Journal of Geodesy》2006,80(7):381-396
The Detection Identification Adaptation (DIA) procedure was applied to the coordinate time-series of some permanent GPS stations belonging to the Italian GPS Fiducial Network (IGFN), of the Italian Space Agency (ASI), to detect discontinuities and to reject outliers. The daily solutions of the stations of Cagliari, Genoa, Medicina, Noto, Turin, Perugia and Venice were computed for the period 1997.0–2003.0 using Bernese GPS software v.4.2. The data were interpolated using a model with a linear term and an annual periodic term. The parameters were estimated by least squares. The DIA procedure was organized to automatically detect discontinuities and outliers. Approximately, 70% of the discontinuities present in the coordinate time-series were identified and their magnitudes were estimated. The identified discontinuities are basically caused by equipment replacement and reference frame changes, but in a few cases the reason is still unknown. With regard to the outliers, roughly 6% of the data were rejected. These data were considered outliers on the base of the level of significance and of the power of the test adopted in this work. Except for the stations of Perugia and Venice, the estimated coordinates agree with ITRF2000 values at the 10 mm level, and the estimated velocities are within a few mm/year of the ITRF2000 values. 相似文献
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125.
浅谈县局计算机网络维护 总被引:9,自引:0,他引:9
对单收站接收机的硬件进行升级后,可在另一台电脑上收看及录制单收站多媒体视频广播;也可在多台电脑上安装Micaps2.0;便于对地面测报网络的维护;电脑系统的维护。 相似文献
126.
动量BP算法在路基沉降预测中的应用 总被引:3,自引:0,他引:3
提出一种采用动量BP算法来预测路基沉降的方法,结合具体的工程实例,构建了预测路基沉降的具体BP神经网络模型。预测结果表明,该模型有较高的预测精度,可作为预测路基沉降的一种新方法。 相似文献
127.
土体中大量降排水的过程实际上是土体中有效应力增长的过程。通过对抽水试验中土体渗透系数的回归分析,建立了渗透系数与有效应力增量之间的耦合响应模型关系,说明降排水过程中土体渗透系数是呈非线性变化的。 相似文献
128.
A Network Model for Dispersion of Communicable Diseases 总被引:3,自引:0,他引:3
The spread of communicable diseases through a population is an intrinsic spatial and temporal process. This paper presents an individual‐based analytical framework for modeling the spatial and temporal heterogeneity in the disease transmission. The framework specifies a network model structure and six associated parameters. These parameters describe the properties of nodes, the properties of links, and the topology of the network. Through this model structure and associated parameters, this framework allows the representation of discrete individuals, individualized interactions, and interaction patterns in a network of human contact. The explicit representation of the spatial distribution and mobility of individuals in particular facilitates the modeling of spatial heterogeneity in the disease transmission. 相似文献
129.
Studies on small-world networks have received intensive interdisciplinary attention during the past several years. It is well-known
among researchers that a small-world network is often characterized by high connectivity and clustering, but so far there
exist few effective approaches to evaluate small-world properties, especially for spatial networks. This paper proposes a
method to examine the small-world properties of spatial networks from the perspective of network autocorrelation. Two network
autocorrelation statistics, Moran’s I and Getis–Ord’s G, are used to monitor the structural properties of networks in a process of “rewiring” networks from a regular to a random
network. We discovered that Moran’s I and Getis–Ord’s G tend to converge and have relatively low values when properties of small-world networks emerge. Three transportation networks
at the national, metropolitan, and intra-city levels are analyzed using this approach. It is found that spatial networks at
these three scales possess small-world properties when the correlation lag distances reach certain thresholds, implying that
the manifestation of small-world phenomena result from the interplay between the network structure and the dynamics taking
place on the network.
相似文献
130.
本文详细介绍了对苏通大桥主桥钢箱梁制造几何控制三维高精度基准网的测设,通过实际工程的实施对高精度三维基准网的方案设计和精度控制进行了有效的探索。 相似文献