共查询到20条相似文献，搜索用时 15 毫秒
1.
M. R. Mosavi 《GPS Solutions》2006,10(2):97-107
Position information obtained from standard global positioning system (GPS) receivers has time variant errors. For effective use of GPS information in a navigation system, it is essential to model these errors. A new approach is presented for improving positioning accuracy using neural network (NN), fuzzy neural network (FNN), and Kalman filter (KF). These methods predict the position components’ errors that are used as differential GPS (DGPS) corrections in real-time positioning. Method validity is verified with experimental data from an actual data collection, before and after selective availability (SA) error. The result is a highly effective estimation technique for accurate positioning, so that positioning accuracy is drastically improved to less than 0.40 m, independent of SA error. The experimental test results with real data emphasize that the total performance of NN is better than FNN and KF considering the trade-off between accuracy and speed for DGPS corrections prediction. 相似文献
2.
A realistic assessment of the total uncertainty budget of Global Positioning System (GPS) observations and its adequate mathematical treatment is a basic requirement for all analysis and interpretation of GPS-derived point positions, in particular GPS heights, and their respective changes. This implies not only the random variability but also the remaining systematic errors. At present in geodesy, the main focus is on stochastic approaches in which errors are modeled by means of random variables. Here, an alternative approach based on interval mathematics is presented. It allows us to model and to quantify the impact of remaining systematic errors in GPS carrier-phase observations on the final results using deterministic error bands. In this paper, emphasis is given to the derivation of the observation intervals based on influence parameters and to the study of the complex linear transfer of this type of uncertainty to estimated point positions yielding zonotopes. From the presented simulation studies of GPS baselines, it turns out that the uncertainty due to remaining systematic effects dominates the total uncertainty budget for baselines longer than 200 km. 相似文献
3.
Michele Dalponte Cristina Martinez Mirco Rodeghiero Damiano Gianelle 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(6):787-797
Ground reference data collection represents an important element in the prediction of stem volume with LiDAR-derived variables, and at present it is the most expensive part of such analyses. In this paper two aspects of ground reference data collection were analyzed: (1) the positioning error of the ground plots; and (2) the optimal number of training plots. A system for the prediction of stem volume at area-based level was adopted. LiDAR data were preprocessed and 13 variables describing both height and coverage were extracted. Models were defined using a stepwise ordinary least square (OLS) regression. Three experiments were conducted: (i) the role of the plots positioning error on prediction accuracy; (ii) the influence of random downsampling of plot numbers on prediction accuracy; and (iii) the influence of a stratified downsampling of plot numbers on prediction accuracy based on LiDAR-derived variables. A dataset comprising 799 ground plots was used. They were distributed throughout a mountainous area in the Southern Alps, where the presence of a complex landscape increases the uncertainty of the Global Positioning System (GPS) accuracy, and where a large variety of tree forest species and climatic environments make it necessary to have a large number of sample plots for accurate characterization of the study area. All the experiments provided important indications for LiDAR based forest inventories: the GPS error did not significantly influence the prediction accuracy and it was possible to reduce the number of training samples without compromising the generalization ability of the prediction model. Leading on from these findings, a new ground sampling protocol based on genetic algorithms was proposed. The new protocol allowed us to obtain promising results for the considered dataset: using only 53 training plots, instead of 534 in the original dataset, we obtained the same results for the validation set. These results, obtained in a complex mountainous area, are representative of Alpine environments and allow us to infer that similar (or better) results could also be obtained within non mountainous areas. 相似文献
4.
We describe a demodulation scheme for the navigation message of GPS receivers on spin-stabilized rockets. Doppler frequencies due to fast and complex dynamics, in particular high-rate spin, cause errors in carrier frequency tracking. The effects of such errors on navigation message demodulation are described through theoretical analysis and numerical simulation. A demodulation scheme that includes a frequency estimator is proposed to account for frequency tracking errors. It is demonstrated that demodulation performance is degraded 5 dB due to frequency uncertainty. Simulation results showed that a demodulator which includes maximum likelihood (ML) frequency estimator achieves near-optimal symbol error rate under these conditions. Demodulation with ML estimator achieves a bit error rate below 10?5 for a C/N 0?=?35 dB–Hz, for spin rates below 2.7?Hz, and a rocket radius smaller than 1 m. For the cases in which computational capabilities of the on-board GPS receiver is insufficient to implement the demodulator with ML estimator, frequency estimation methods with low complexity were also tested through numerical simulation. The proposed Kay and Quinn-Fernandes combination achieves a bit error rate below 10?5 for a C/N 0?=?37 dB–Hz while requiring 1/10 of processing time. 相似文献
5.
Spatial predictions of forest variables are required for supporting modern national and sub-national forest planning strategies, especially in the framework of a climate change scenario. Nowadays methods for constructing wall-to-wall maps and calculating small-area estimates of forest parameters are becoming essential components of most advanced National Forest Inventory (NFI) programs. Such methods are based on the assumption of a relationship between the forest variables and predictor variables that are available for the entire forest area. Many commonly used predictors are based on data obtained from active or passive remote sensing technologies. Italy has almost 40% of its land area covered by forests. Because of the great diversity of Italian forests with respect to composition, structure and management and underlying climatic, morphological and soil conditions, a relevant question is whether methods successfully used in less complex temperate and boreal forests may be applied successfully at country level in Italy.For a study area of more than 48,657 km2 in central Italy of which 43% is covered by forest, the study presents the results of a test regarding wall-to-wall, spatially explicit estimation of forest growing stock volume (GSV) based on field measurement of 1350 plots during the last Italian NFI. For the same area, we used potential predictor variables that are available across the whole of Italy: cloud-free mosaics of multispectral optical satellite imagery (Landsat 5 TM), microwave sensor data (JAXA PALSAR), a canopy height model (CHM) from satellite LiDAR, and auxiliary variables from climate, temperature and precipitation maps, soil maps, and a digital terrain model.Two non-parametric (random forests and k-NN) and two parametric (multiple linear regression and geographically weighted regression) prediction methods were tested to produce wall-to-wall map of growing stock volume at 23-m resolution. Pixel level predictions were used to produce small-area, province-level model-assisted estimates. The performances of all the methods were compared in terms of percent root mean-square error using a leave-one-out procedure and an independent dataset was used for validation. Results were comparable to those available for other ecological regions using similar predictors, but random forests produced the most accurate results with a pixel level R2 = 0.69 and RMSE% = 37.2% against the independent validation dataset. Model-assisted estimates were more precise than the original design-based estimates provided by the NFI. 相似文献
6.
本文从分析航空重力向下延拓过程中偶然误差和系统误差的变化特性入手,进而提出处理办法。首先,利用试验说明移去恢复法局限性,同时表明需处理系统误差和偶然误差的必要性。然后,采用理论推演和数值模拟计算分别估计了系统误差和偶然误差影响,试验结果发现:系统误差影响和偶然误差影响均与数据格网间隔、向下延拓高度呈线性关系,当格网化间隔较小和延拓高度较高时系统误差影响和偶然误差影响较大。最后,提出使用半参数模型和正则化算法的两步法估计系统误差和减弱偶然误差影响,试验结果说明两步法处理向下延拓各类误差影响优于仅用半参数模型或正则化算法的结果,在试验数据的偶然误差标准差为2×10~(-5) m/s~2、恒值系统误差3×10~(-5) m/s~2和变值系统误差标准差约1.3×10~(-5) m/s~2时,以及向下延拓高度6.3 km和格网间隔6′的条件下,两步法向下延拓结果的精度可达2.3×10~(-5) m/s~2。 相似文献
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9.
Accuracy assessment of the GPS-TEC calibration constants by means of a simulation technique 总被引：2，自引：2，他引：0
During the last 2 decades, Global Positioning System (GPS) measurements have become a very important data-source for ionospheric
studies. However, it is not a direct and easy task to obtain accurate ionospheric information from these measurements because
it is necessary to perform a careful estimation of the calibration constants affecting the GPS observations, the so-called
differential code biases (DCBs). In this paper, the most common approximations used in several GPS calibration methods, e.g.
the La Plata Ionospheric Model (LPIM), are applied to a set of specially computed synthetic slant Total Electron Content datasets
to assess the accuracy of the DCB estimation in a global scale scenario. These synthetic datasets were generated using a modified
version of the NeQuick model, and have two important features: they show a realistic temporal and spatial behavior and all
a-priori DCBs are set to zero by construction. Then, after the application of the calibration method the deviations from zero
of the estimated DCBs are direct indicators of the accuracy of the method. To evaluate the effect of the solar activity radiation
level the analysis was performed for years 2001 (high solar activity) and 2006 (low solar activity). To take into account
seasonal changes of the ionosphere behavior, the analysis was repeated for three consecutive days close to each equinox and
solstice of every year. Then, a data package comprising 24 days from approximately 200 IGS permanent stations was processed.
In order to avoid unwanted geomagnetic storms effects, the selected days correspond to periods of quiet geomagnetic conditions.
The most important results of this work are: i) the estimated DCBs can be affected by errors around ±8 TECu for high solar
activity and ±3 TECu for low solar activity; and ii) DCB errors present a systematic behavior depending on the modip coordinate,
that is more evident for the positive modip region. 相似文献
10.
分析了高精度GPS形变监测网数据处理中系统误差的影响,给出了顾及系统误差影响的自由网平差模型;针对粗差在GPS观测数据中存在的广泛性,在对平差模型进行整体性检验的基础上,采用检验方法消除粗差对平差结果的影响;结合抗差估计,对中国地壳运动观测网络工程1999~2003年观测数据进行了处理,验证了模型的精度和可靠性。 相似文献
11.
GPS沉降观测的实践及减弱误差的措施 总被引：2，自引：0，他引：2
利用方差分析的方法计算了一个实际的GPS沉降观测中的系统误差和偶然误差，结果表明系统误差远大于偶然误差，此外还提出了减弱误差的必要措施。 相似文献
12.
The purpose of this study was to compare a number of state-of-the-art methods in airborne laser scanning (ALS) remote sensing with regards to their capacity to describe tree size inequality and other indicators related to forest structure. The indicators chosen were based on the analysis of the Lorenz curve: Gini coefficient (GC), Lorenz asymmetry (LA), the proportions of basal area (BALM) and stem density (NSLM) stocked above the mean quadratic diameter. Each method belonged to one of these estimation strategies: (A) estimating indicators directly; (B) estimating the whole Lorenz curve; or (C) estimating a complete tree list. Across these strategies, the most popular statistical methods for area-based approach (ABA) were used: regression, random forest (RF), and nearest neighbour imputation. The latter included distance metrics based on either RF (NN–RF) or most similar neighbour (MSN). In the case of tree list estimation, methods based on individual tree detection (ITD) and semi-ITD, both combined with MSN imputation, were also studied. The most accurate method was direct estimation by best subset regression, which obtained the lowest cross-validated coefficients of variation of their root mean squared error CV(RMSE) for most indicators: GC (16.80%), LA (8.76%), BALM (8.80%) and NSLM (14.60%). Similar figures [CV(RMSE) 16.09%, 10.49%, 10.93% and 14.07%, respectively] were obtained by MSN imputation of tree lists by ABA, a method that also showed a number of additional advantages, such as better distributing the residual variance along the predictive range. In light of our results, ITD approaches may be clearly inferior to ABA with regards to describing the structural properties related to tree size inequality in forested areas. 相似文献
13.
机载LiDAR数据估算样地和单木尺度森林地上生物量 总被引：2，自引：0，他引：2
利用机载激光雷达点云数据,结合大量实测单木结构信息,分别从样地和单木尺度估算了森林地上生物量AGB。首先,利用局部最大值单木提取算法提取了每个样地内的单木结构参数,并针对样地和单木尺度分别计算了一组激光雷达变量。然后,利用激光雷达变量和地上生物量及其两者的对数形式,从样地和单木尺度分别构建了估算模型。最后,针对两种尺度估算过程中存在的不确定性进行了详细讨论。结果表明:(1)样地和单木尺度模型估算的森林地上生物量与地面实测值都具有明显的相关性,且对数模型估算效果要优于非对数模型;(2)样地尺度模型估算效果(R2=0.84,rRMSE=0.23)明显优于单木尺度模型(R2=0.61,rRMSE=0.46);(3)按树木类型分别进行估算可以提高单木地上生物量的估算精度;(4)不论是样地还是单木尺度地上生物量估算都存在一定的不确定性,与样地尺度相比,单木尺度估算过程的不确定性更大,这种不确定性主要来自单木识别过程。 相似文献
14.
Estimation of forest aboveground biomass (AGB) is informative of the role of forest ecosystems in local and global carbon budgets. There is a need to retrospectively estimate biomass in order to establish a historical baseline and enable reporting of change. In this research, we used temporal spectral trajectories to inform on forest successional development status in support of modelling and mapping of historic AGB for Mediterranean pines in central Spain. AGB generated with ground plot data from the Spanish National Forest Inventory (NFI), representing two collection periods (1990 and 2000), are linked with static and dynamic spectral data as captured by Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) sensors over a 25 year period (1984–2009). The importance of forest structural complexity on the relationship between AGB and spectral vegetation indices is revealed by the analysis of wavelet transforms. Two-dimensional (2D) wavelet transforms support the identification of spectral trajectory patterns of forest stands that in turn, are associated with traits of individual NFI plots, using a flexible algorithm sensitive to capturing time series similarity. Single-date spectral indices, temporal trajectories, and temporal derivatives associated with succession are used as input variables to non-parametric decision trees for modelling, estimation, and mapping of AGB and carbon sinks over the entire study area. Results indicate that patterns of change found in Normalized Difference Vegetation Index (NDVI) values are associated and relate well to classes of forest AGB. The Tasseled Cap Angle (TCA) index was found to be strongly related with forest density, although the related patterns of change had little relation with variability in historic AGB. By scaling biomass models through small (∼2.5 ha) spatial objects defined by spectral homogeneity, the AGB dynamics in the period 1990–2000 are mapped (70% accuracy when validated with plot values of change), revealing an increase of 18% in AGB irregularly distributed over 814 km2 of pines. The accumulation of C calculated in AGB was on average 0.65 t ha−1 y−1, equivalent to a fixation of 2.38 t ha−1 y−1 of carbon dioxide. 相似文献
15.
利用神经网络预测的GPS/SINS组合导航系统算法研究 总被引：2，自引：0，他引：2
提出了一种基于神经网络预测的GPS/SINS组合导航系统算法。GPS信号可用时,该算法分别将惯性传感器的输出以及卡尔曼滤波器的输出信息作为神经网络的输入及理想输出信息,并进行在线训练;当GPS信息失锁时,利用已经训练好的神经网络预测各导航参数误差,并校正SINS。地面静态实验与动态跑车实验结果证明了该方法的可行性与有效性。 相似文献
16.
粗差检测与抗差估计相结合的方法在动态相对定位中的应用 总被引：2，自引：0，他引：2
分析了粗差对GPS动态相对定位的影响,给出了相应的影响函数和抗差估计方法。建议采用粗差探测与抗差估计相结合的方法来处理GPS动态定位中的粗差问题。抗差估计中的等价权分别采用了IGG3方案和双因子等价权函数,对两种方案的效果进行比较和分析,并利用实测数据对所提方法的实际效果进行了检验。结果表明,基于粗差探测和抗差估计相结合的粗差处理方法可有效控制和抵御粗差的影响;分别采用IGG3方案和双因子等价权函数的定位结果差异较小。 相似文献
17.
The main scope of this research is to assess the ultimate accuracy that can be achieved for the slant total electron content
(sTEC) estimated from dual-frequency global positioning system (GPS) observations which depends, primarily, on the calibration
of the inter-frequency biases (IFB). Two different calibration approaches are analyzed: the so-called satellite-by-satellite
one, which involves levelling the carrier-phase to the code-delay GPS observations and then the IFB estimation; and the so-called
arc-by-arc one, which avoids the use of code-delay observations but requires the estimation of arc-dependent biases. Two strategies
are used for the analysis: the first one compares calibrated sTEC from two co-located GPS receivers that serve to assess the
levelling errors; and the second one, assesses the model error using synthetic data free of calibration error, produced with
a specially developed technique. The results show that the arc-by-arc calibration technique performs better than the satellite-by-satellite
one for mid-latitudes, while the opposite happens for low-latitudes. 相似文献
18.
提出了一种基于增广参数Kalman滤波的多路径效应系统误差估计方法,将系统误差作为状态参数,并对其建立一阶AR模型,同时利用多路径重复性特性,更新多路径误差改正模型,在一定程度上解决了固定多路径误差模型随着时间推移重复性减小而有效性降低的问题,并利用16d实测数据例证了本方法具有一定的可行性和有效性。 相似文献
19.
We study the characteristics of the random GPS positioning errors when the pseudorange errors differ for each satellite. A concise, explicit, analytical formula is derived for the covariance of the positioning error by using singular value decomposition. It is composed of a uniform error covariance together with additional contributions from those satellites with larger pseudorange errors. The eigenvectors of the uniform error covariance define the principal directions of the 4-dimensional error ellipsoid, and the eigenvalues are the squares of the semi-axes. The additional part from individual satellites has only one eigenvector and one eigenvalue. This makes the error ellipsoid enlarge mainly along a direction related to both the overall satellite geometry and the position of the specific satellites. The theory is validated by simulating the GPS constellation and pseudorange measurements. The random positioning error is examined while any one or more pseudorange errors are increased. Horizontal positioning error distributions are presented to demonstrate the variations of the orientation and size of the error ellipses with the pseudorange error of a specific satellite. The results show that the analytical formula describes the positioning error accurately. 相似文献
20.
基于经验模态分解的GPS基线解算模型 总被引：1，自引：1，他引：0
非建模系统误差是影响高精度GPS基线解算精度的一个重要因素,文章给出基于经验模态分解的GPS基线解算模型,有效消弱系统误差对基线解的影响。在现有经验模态分解理论的基础上,定义经验模态分解的多尺度分解与重构结构,并由此给出基于经验模态的系统趋势分离模型,依据累积标准化模量的均值随尺度的变化确定系统误差与噪声分离尺度的选择标准。给出基于经验模态分解的GPS基线解算的技术路线,首先计算GPS相位双差观测方程的浮点解残差序列,分离出系统误差并用于修正GPS双差观测值,重新计算双差浮点解,采用Lambda算法固定整周模糊度,计算固定基线解,从而消弱系统误差对基线解算的影响,提高基线固定解的可靠性。并采用实测GPS数据验证模型,F-ratio指数与W-ratio指数表明系统误差消弱后,基线固定解可靠性得到明显提高,重新计算的残差序列表明系统误差得到很好的消弱。 相似文献