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Siyao Wang Bofeng Li Xingxing Li Nan Zang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(1):385-401
Integer ambiguity fixing with uncalibrated phase delay (UPD) products can significantly shorten the initialization time and improve the accuracy of precise point positioning (PPP). Since the tracking arcs of satellites and the behavior of atmospheric biases can be very different for the reference networks with different scales, the qualities of corresponding UPD products may be also various. The purpose of this paper is to comparatively investigate the influence of different scales of reference station networks on UPD estimation and user ambiguity resolution. Three reference station networks with global, wide-area and local scales are used to compute the UPD products and analyze their impact on the PPP-AR. The time-to-first-fix, the unfix rate and the incorrect fix rate of PPP-AR are analyzed. Moreover, in order to further shorten the convergence time for obtaining precise positioning, a modified partial ambiguity resolution (PAR) and corresponding validation strategy are presented. In this PAR method, the ambiguity subset is determined by removing the ambiguity one by one in the order of ascending elevations. Besides, for static positioning mode, a coordinate validation strategy is employed to enhance the reliability of the fixed coordinate. The experiment results show that UPD products computed by smaller station network are more accurate and lead to a better coordinate solution; the PAR method used in this paper can shorten the convergence time and the coordinate validation strategy can improve the availability of high precision positioning. 相似文献
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词汇教学中的问题思考 总被引:1,自引:0,他引:1
吴红 《华北航天工业学院学报》2003,13(4):57-59
词汇的记忆与掌握,对以后词汇的灵活和正确使用是非常必要的。对于任何语言的初学者来说,词汇的掌握都是一个繁重的任务。传统的词汇教学往往把重点放在学生的业余时间对词汇的机械记忆上,可是这种方法忽略了在课堂上来自于教师指导的重要性。本文建议每位教师在课堂上应该尝试创造不同的形式,以便学生能够积极主动而不是被动地学习词汇。 相似文献
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谢红桂 《长沙航空职业技术学院学报》2006,6(3):72-74
社会通称表现出了多元化的发展趋势,出现了社会通称的缺位。人们在对社会通称的使用中表现出一种明显的语用模糊。这种语用模糊虽然违背了语言交流中的会话原则,但是有效地弥补了当代社会通称缺位所带来的不便。 相似文献
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比相法瞬时测频在电子对抗和空馈式雷达目标模拟领域占据重要地位。首先,介绍了比相法瞬时测频原理,设计了利用四路鉴相器实现瞬时测频的方法,并重点研究了四路鉴相器由低位向高位解模糊方法,给出了解模糊前后鉴相器二进制位构成和具体解模糊过程,该方法具有重要的工程参考价值。 相似文献
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The middle pulse repetition frequency(MPRF)and high pulse repetition frequency(HPRF)modes are widely adopted in airborne pulse Doppler(PD)radar systems,which results in the problem that the range measurement of targets is ambiguous.The existing data processing based range ambiguity resolving methods work well on the condition that the signal-to-noise ratio(SNR)is high enough.In this paper,a multiple model particle flter(MMPF)based track-beforedetect(TBD)method is proposed to address the problem of target detection and tracking with range ambiguous radar in low-SNR environment.By introducing a discrete variable that denotes whether a target is present or not and the discrete pulse interval number(PIN)as components of the target state vector,and modeling the incremental variable of the PIN as a three-state Markov chain,the proposed algorithm converts the problem of range ambiguity resolving into a hybrid state fltering problem.At last,the hybrid fltering problem is implemented by a MMPF-based TBD method in the Bayesian framework.Simulation results demonstrate that the proposed Bayesian approach can estimate target state as well as the PIN simultaneously,and succeeds in detecting and tracking weak targets with the range ambiguous radar.Simulation results also show that the performance of the proposed method is superior to that of the multiple hypothesis(MH)method in low-SNR environment. 相似文献
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针对高分辨率宽测绘带合成孔径雷达(High Resolution Wide Swath Synthetic Aperture Radar, HRWS SAR)在俯仰向波束形成受地面目标高程影响造成增益损失以及在方位向非均匀采样造成模糊的问题,文中提出了一种基于压缩感知(Compressed Sensing, CS)技术的HRWS SAR成像算法。根据SAR系统和平台参数建立精确的观测模型后,通过求解优化问题直接准确地估计出了在地面高程变化影响下的目标来波方向(Direction of Arrival, DOA)并重建了非均匀采样下的方位向观测场景,从而实现了HRWS SAR在俯仰向和方位向的非模糊成像。仿真结果表明了本文算法的有效性。 相似文献