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陆基增强系统(GBAS)是利用载波相位平滑伪距差分修正实现对导航辅助定位的. 其中,平滑时间常数是影响载波相位平滑伪距精度的关键参数. 本文分析研究了不同平滑时间下电离层时间梯度和空间梯度对Hatch滤波的影响. 在结合电离层时空梯度和多径效应引起的滤波总误差方差的基础上,推导出自适应的最优平滑时间常数. 分别对GBAS静态和动态两种环境下的定位误差进行实验,实验结果表明,采用本文推导出的自适应平滑时间常数降低了GBAS伪距测量误差,从而使定位精度得到增强. 相似文献
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高光谱遥感影像具有光谱分辨率极高的特点,承载了大量可区分不同类型地物的诊断性光谱信息以及区分亚类相似地物之间细微差别的光谱信息,在目标探测领域具有独特的优势。与此同时,高光谱遥感影像也带来了数据维数高、邻近波段之间存在大量冗余信息的问题,高维度的数据结构往往使得高光谱影像异常目标类和背景类之间的可分性降低。为了缓解上述问题,本文提出了一种基于波段选择的协同表达高光谱异常探测算法。首先,使用最优聚类框架对高光谱波段进行选择,获得一组波段子集来表示原有的全部波段,使得高光谱影像异常目标类与背景类之间的可分性增强。然后使用协同表达对影像上的像元进行重建,由于异常目标类和背景类之间的可分性增强,对异常目标像元进行协同表达时将会得到更大的残差,异常目标像元的输出值增大,可以更好地实现异常目标和背景类的分离。本文使用了3组高光谱影像数据进行异常目标探测实验,实验结果表明,该方法与其他现有高光谱异常目标探测算法对比,曲线下面积AUC(Area Under Curve)值更高,可以更好地实现异常目标与背景分离,能够更有效地对高光谱影像进行异常目标探测。 相似文献
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Soil surface roughness (SSR) is an important factor in controlling sediment and runoff generation, influencing directly a wide spectrum of erosion parameters. SSR is highly variable in time and space under natural conditions, and characterizing SSR to improve the parameterization of hydrological and erosion models has proved challenging. Our study uses recent technological and algorithmic developments in capturing and processing close aerial sensing data to evaluate how high-resolution imagery can assist the temporally and spatially explicit monitoring of SSR. We evaluated the evolution of SSR under natural rainfall and growing vegetation conditions on two arable fields in Denmark. Unmanned aerial vehicle (UAV) photogrammetry was used to monitor small field plots over 7 months after seeding of winter wheat following conventional and reduced tillage treatments. Field campaigns were conducted at least once a month from October until April, resulting in nine time steps of data acquisition. Structure from motion photogrammetry was used to derive high-resolution point clouds with an average ground sampling distance of 2.7 mm and a mean ground control point accuracy of 1.8 mm. A comprehensive workflow was developed to process the point clouds, including the detection of vegetation and the removal of vegetation-induced point cloud noise. Rasterized and filtered point clouds were then used to determine SSR geostatistically as the standard deviation of height, applying different kernel sizes and using semivariograms. The results showed an influence of kernel size on roughness, with a value range of 0.2–1 cm of average height deviation during the monitoring period. Semivariograms showed a measurable decrease in sill variance and an increase in range over time. This research demonstrated multiple challenges to measuring SSR with UAV under natural conditions with increasing vegetation cover. The proposed workflow represents a step forward in tackling those challenges and provides a knowledge base for future research. © 2020 John Wiley & Sons, Ltd. 相似文献
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一种基于熵权法的小波去噪复合评价指标 总被引:2,自引:0,他引:2
传统的评价指标在真值未知的情况下不能满足小波去噪质量评价的要求。为此,借助变化率特征重新构建均方根误差变化量和平滑度变化量两个指标,利用熵权法定权将归一化后的两个指标线性组合,所得到的新指标即为复合评价指标。该方法借助指标的变化率随分解层数的增加表现出明显的收敛特性来确定去噪最优分解层数。实验表明,该方法能够在真值未知的情况下准确地指导小波分解,确定去噪最优分解层数,从而达到最优去噪效果。 相似文献
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以广播星历为起算轨道的北斗卫星实时滤波精密定轨往往需要较长收敛时间,针对此,提出利用超快速精密星历约束的实时精密定轨方法。通过MGEX跟踪网全球分布的51个测站连续7 d的实测数据,利用平方根信息滤波对北斗卫星实时精密轨道进行确定,并以3 d解事后轨道作为参考,评估北斗卫星实时滤波轨道精度。结果表明,利用广播星历作起算轨道时,北斗实时滤波轨道平均需要经过15 h收敛才能达到稳定,而新方法在这段时间内轨道变化较为平稳,未出现明显的收敛现象,并且7 d时间内GEO卫星在切向、法向和径向上RMS分别优于2.5 m、20 cm和30 cm,IGSO和MEO卫星在3个方向上分别优于30 cm、15 cm和10 cm。 相似文献
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At present, there is less theoretical research and practical experience in the aspect of ultra-shallow seismic exploration to the target layers at depths of only tens of meters both at home and abroad. Seismic exploration plays an important role in the location of faults and active structures, but the depth dozens of meters below the ground surface is the blind area of any kind of deep and shallow seismic exploration. Starting from the point of view of detecting urban active faults, and using related theories and methods of geology, geophysics and mathematics, the paper discusses the preconditions for acquiring efficient ultra-shallow seismic survey results in complicated geological backgrounds in Qingdao. Taking the Qingdao area as an example in this paper, we study the depth condition of Quaternary deposits, and apply 4-8 stacking folds to satisfy the requirement to get the exploration results with high-resolution and high-SNR. Preliminary results reveal that selecting a proper surveillance layout is one of the keys to acquire authentic exploration results in ultra-shallow P-wave reflection exploration. Our results also show that ultra-shallow seismic reflection method in detecting faults in the Qingdao area has good application prospects. 相似文献
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The quality of GIServices (QoGIS) is an important consideration for services sharing and interoperation. However, QoGIS is a complex concept and difficult to be evaluated reasonably. Most of the current studies have focused on static and non-scalable evaluation methods but have ignored location sensitivity subsequently resulting in the inaccurate QoGIS values. For intensive geodata and computation, GIServices are more sensitive to the location factor than general services. This paper proposes a location-aware GIServices quality prediction model via collaborative filtering (LAGCF). The model uses a mixed CF method based on time zone feature from the perspectives of both user and GIServices. Time zone is taken as the location factor and mapped into the prediction process. A time zone-adjusted Pearson correlation coefficient algorithm was designed to measure the similarity between the GIServices and the target, helping to identify highly similar GIServices. By adopting a coefficient of confidence in the final generation phase, the value of the QoGIS most similar to the target services will play a dominant role in the comprehensive result. Two series of experiments on large-scale QoGIS data were implemented to verify the effectivity of LAGCF. The results showed that LAGCF can improve the accuracy of QoGIS prediction significantly. 相似文献