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231.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(1):650-662
Multipath effects on code observables account for one of the major error sources in high-accuracy Global Positioning System (GPS)-based positioning, atmosphere sounding and timing applications. The multipath hemispherical model (MHM) represents one of the most widely used methods of mitigating code multipath effects by taking advantage of their spatial repeatability. The use of MHM usually assumes that the receiver code biases (RCBs) are time-invariant; however, this assumption is not always valid, as RCBs and linear combinations thereof (differential code biases, for instance) have long been found to be time-varying over a period of one day. In this contribution, we propose an extended multipath hemispherical model (EMHM) that is capable of mitigating the code multipath effects in the presence of time-varying RCBs. Consequently, the proposed EMHM has two advantages. First, the EMHM gives rise to code multipath corrections with improved reliability because it addresses the intraday variability of RCBs. Second, more interestingly, the EMHM allows easy and effective calibration of short-term temporal variations, if any, in the RCB on each frequency. These advantages are hopeful to benefit GPS code-related applications. 相似文献
232.
根据光纤陀螺光纤环受温度效应影响的机理,分析了光纤陀螺零偏产生温度误差的原因,提出了光纤陀螺基于光纤环附近多点温度的误差补偿方法,建立光纤陀螺零偏随光纤环附近多点温度及温度变化率变化的数学补偿模型。根据全温温度实验,分析光纤陀螺零偏随温度变化的规律,确定补偿模型的补偿系数,对光纤陀螺零偏进行温度误差补偿。并将多点温度补偿方法与传统的基于单点温度补偿方案的补偿效果进行对比分析。结果表明,基于两点及以上温度的温度误差补偿模型能将全温零偏稳定性降低2个数量级,全温极差降低1个数量级,优于基于单点类的温度补偿方案,且具有很高的工程应用价值。 相似文献
233.
为了评估GPS L1频点信号体制转换前后的空间信号质量,基于高增益天线接收系统采集数据,对相干自适应副载波调制(CASM)调制和QPSK调制信号质量进行对比分析。首先,简要介绍CASM调制模型,利用波形匹配技术求解L1频点授权信号伪码序列。其次,基于星座图分布和极大似然估计分别解决出QPSK和CASM调制信号分量功率分配难题。最后定量地利用相关特性参数中的S曲线过零点偏差(SCB)和相关损失(CL)对比分析L1频点信号体制转换前后各信号分量空间信号质量。该文结果可为不同信号体制下空间信号质量评估对比提供参考。 相似文献
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《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2645-2661
Timing group delay (TGD) is an important parameter that affects the positioning performance of global navigation satellite systems (GNSS). The BeiDou navigation satellite system (BDS) broadcasts TGD corrections from B3I frequency to B1I and B2I frequencies, namely TGD1 and TGD2. On July 21, 2017, BDS updated TGD values with a maximum change of more than 4 ns. In this contribution, we explain the motivation for the BDS TGD update, which is due to the systematic bias between narrowly correlated and widely correlated pseudo-ranges in BDS monitoring receivers. To investigate the impact of the updated TGD, BDS signal-in-space range error (SISRE) and user positioning performance regarding single point positioning (SPP) and precise point positioning (PPP) are analyzed. Results show that after the update of TGD, the difference between the new TGD and multi-GNSS experiment (MGEX) differential code bias (DCB) decreases from 1.38 ns to 0.29 ns on TGD1 and from 0.40 ns to 0.25 ns on TGD2. With the contribution of more accurate TGD, the systematic bias of BDS radial SISRE no longer exists, and the overall BDS SISRE also reduces from 1.33 m to 0.87 m on B1I/B2I frequency, from 1.05 m to 0.89 m on B1I frequency, from 0.92 m to 0.91 m on B2I frequency, respectively, which proves the similar precision of BDS TGD and MGEX DCB. One week of statistical results from 28 globally distributed MGEX stations shows that the SPP performance improves on non-B3I frequencies after the TGD update, with a maximum improvement of more than 22% for the B1I/B2I or B1I/B3I combination. The new TGD mainly reduces SPP positioning bias in the East component. The updated TGD also slightly improves the PPP convergence performance for the B1I/B3I combination, but mostly contributes to a more accurate estimation of the receiver clock and ambiguities. 相似文献
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Siavash Iran Pour Tilo Reubelt Nico Sneeuw 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Drawing on experience from Gravity Recovery and Climate Experiment (GRACE) data analysis, the scientific challenges were already identified in several studies. Any future mission should focus on improvement in both precision and resolution in space and time. For future gravity missions which use high quality sensors, aliasing of high frequency time-variable geophysical signals to the lower frequency signals is one of the most serious problems. The aliasing problem and the spatio-temporal resolution are mainly restricted by two sampling theorems describing the space-time sampling of satellite missions: (i) a Heisenberg-like uncertainty theorem which states that the product of spatial resolution and time resolution is constant, and (ii) the Colombo–Nyquist rule (CNR), which requires the number of satellite revolutions in a repeat period to be at least twice a given maximum spherical harmonic degree. The CNR holds under the assumption of equal ground-track spacing, and limits the spatial resolution of the gravity solution. 相似文献
239.
人为差错是影响航空安全的重要风险因素之一。文章根据飞机驾驶人因特点,结合具体飞行任务,基于模糊推理系统构建飞机驾驶人为差错风险量化模型,以识别飞机操纵过程中关键人为差错并确定人为差错的风险严重性,进而评估航空飞行安全。该方法不仅考虑了人为差错的概率,还考虑了人为差错对驾驶舱系统的影响,并提出了人为差错概率、差错影响概率和人为差错后果作为驾驶舱人为差错风险评估的量化指标。选择进近阶段任务作为研究对象并进行案例分析,实验结果表明,该模型能够精确描述人为差错风险严重性与风险指标之间的关系,降低了专家判断的主观性对结果的影响,且有效解决了数据不足引起的不确定性等问题。 相似文献
240.