基于第一类无奇点根数的LEO历书参数设计

GNSS技术蓬勃发展,在国防建设和国民经济发展中发挥了重要作用。但也因其无法快速解算整周模糊度、复杂环境下适应性差、完好性差等缺点,限制了其作用的最大发挥。基于LEO通信卫星星座的系统增强可以很好地克服这些缺点。要实现该增强系统,基础之一就是如何生成LEO卫星的历书星历。为解决这个问题,从第一类无奇点出发对GPS标准历书进行改造,提出了一套专用于LEO卫星的10参数历书集,并推导了历书计算公式。对600~1 500 km轨道高度的2~7 d的LEO卫星轨道进行了拟合实验。结果表明,高度600 km时长2 d,高度700 km时长4 d,高度800 km时长7 d历书拟合的用户距离误差(URE)的均方根误差(RMS)分别优于936.021,944.087和956.183 m。     

GNSS数据处理中双差残差恢复单差残差的原理分析

根据零基线或超短基线相对定位的双差残差可以对GNSS观测数据质量进行评估,但双差残差包含了参考卫星观测误差的影响,不利于对各颗卫星观测误差特性进行独立分析。分析了RTKLIB软件中双差残差恢复单差残差方法的原理,从理论上论证了根据恢复的单差残差序列进行观测数据质量评估的合理性,并利用一组30 m基线GPS双频实测数据对此进行数值验证。     

Port Infrastructure Control (Madeira Island,Portugal) through a Hybrid Monitoring System (GNSS and Accelerometers)

This article describes the implementation of a monitoring system on the breakwater at the Funchal Port (Madeira Island, Portugal) for the purpose of understanding its dynamic behavior and the temporal evolution of structural health. The monitoring system focuses on the breakwater superstructure and aims to identify the evolution of damage on the breakwater and analyze the impact of cruise ships docking and undocking. The system includes the measurement of displacements through geodetic techniques using global navigation satellite systems and the measurement of vibrations using accelerometers. Ten observation campaigns were performed over almost 3 years. As the measured displacements during this period were less than 7.5 mm it can be concluded that, despite some visible cracks, the breakwater superstructure did not suffer significant structural changes. It was shown from the measured acceleration records that some of the main modal parameters could be identified, namely the main natural frequencies of the superstructure. Through an analysis of the natural frequencies progression over time, it will be possible to identify deterioration effects on the foundation and/or the superstructure. The comparison of natural frequencies identified could be useful to evaluate the impact of these events on structural health.     

Main Frontal thrust deformation and topographic growth of the Mohand Range,northwest Himalaya

The Main Frontal thrust (MFT) uplifts the Himalayan topographic front. Deciphering MFT deformation kinematics is crucial for understanding how the orogen accommodates continuing continental collision and assessing associated hazards. Here, we (a) detail newly discovered fault-zone exposures along the MFT at the Mohand Range front in northwestern India and (b) apply contemporary fault zone theory to show that the MFT is an emergent fault with a well-developed fault zone overlain by uplifted Quaternary gravels over a horizontal length of ∼700 m. Northward from the front, the fault zone grades from a central, gouge-dominated core to a hanging-wall, rock-dominated damage zone. We observed incohesive, non-foliated breccia, fault gouge, and brittle deformation microstructures within the fractured country rocks (Middle Siwaliks) and outcrop scale, non-plunging folds in the proximal hanging wall. We interpret these observations to suggest that (1) elastico-frictional (brittle) deformation processes operated in the fault zone at near surface (∼1–5 km depth) conditions and (2) the folds formed first at the propagating MFT fault tip, then were subsequently dismembered by the fault itself. Thus, we interpret the Mohand Range as a fault-propagation fold driven by an emergent MFT in contrast to the consensus view that it is a fault-bend fold. A fault-propagation fold model is more consistent with these new observations, the modern range-scale topography, and existing erosion estimates. To further evaluate our proposed structural model, we used a Boundary Element Method-based dislocation model to simulate topographic growth from excess slip at a propagating fault tip. Results show that the frontal topography could have evolved by slip along a (a) near-surface fault plane consistent with the present-day MFT location, or (b) blind MFT at ∼3 km depth farther north near the drainage divide. Comparing modelled vs. measured high resolution (∼16 cm) topographic profiles for each case provides permissible end-member scenarios of an either dynamically-evolving, high erosion, northward-migrating frontal scarp or a static, low, and symmetric, MHT-related fold, respectively. Our integrated approach is expected to deliver an improved understanding of coupled fault-generated deformation and topographic growth that may be applied more broadly across the entire Himalayan front.     

GNSS时间序列中随机漫步消噪的改进半软阈值算法及其评估

全球导航卫星定位系统在卫星定轨和信号质量等方面存在的差异性,造成GNSS时间序列中的随机漫步噪声十分复杂,已经成为制约GNSS技术在高精度变形监测行业领域深入应用的瓶颈。本文针对具有量级小、频率低、敏感性差等复杂特征的随机漫步噪声,提出了一种改进的半软阈值算法,通过引入可变因子形成了统一的半软阈值函数体系,提高了常规半软阈值对随机漫步噪声的适应性。为了验证和评估改进半软阈值算法的效果,利用MATLAB平台仿真生成有线性趋势项、年周期项和随机漫步噪声的GNSS时间序列,共1700个历元。结果表明,改进的半软阈值法较经典方法在信噪比和均方根误差上表现出更加优良的性能。自相关分析的评估结果表明,改进方法所消除的噪声与随机漫步噪声在形态特征上具有高度的一致性。谱指数分析评估结果,进一步从定量角度验证了改进方法对随机漫步噪声的特有适用性。     

GNSS偏心观测在卫星天线定位定向中的应用

由于现地观测条件限制,GNSS天线无法架设在需要观测的目标点上,无法实现精确对中观测目标所对应的地面点中心,此时就需要进行GNSS偏心观测。文中从解决卫星天线定位定向的工程出发,研究GNSS偏心观测三角形法和经纬仪交会法计算归心元素。依据模拟实测计算结果以及实际卫星天线定位定向的结果,分析了两种方法的优缺点。     

GNSS观测数据质量对坐标解算精度的影响分析

针对陆态网络流动GNSS观测环境的变化易引起观测质量下降的问题,该文对其不同观测质量数据解算坐标误差进行分析,以便于根据不同研究区域选择不同质量的观测数据。以华北地区450个流动GNSS站为研究对象,统计结果表明,单天坐标精度总体上随着数据有效率的增大而升高,随M1和M2增大而降低,多路径效应对测站垂向的影响大于水平向;在影响测站观测环境的诸多因素中,树木遮挡影响最大。最后提出了提高数据质量的建议措施。     

附有长度约束的模糊度解算方法比较

整周模糊度解算方法的合理选择是GNSS定向处理中的关键问题,针对此问题,该文对GNSS定向中的LAMBDA_C和CLAMBDA两种附有基线长约束的模糊度固定方法的性能进行了详细的对比分析。结果显示,相对于经典的基于Ratio检验的LAMBDA算法,LAMBDA_C和CLAMBDA均可提高模糊度固定率和正确率,尤其是在单频单系统下提高效果更为显著;CLAMBD的总体固定效果略优于LAMBDA_C,但后者的解算效率更高。     

GNSS遥感研究与应用进展和展望

全球导航卫星系统遥感(GNSS remote sensing)属卫星导航应用与遥感的一个交叉学科范畴。GNSS系统除传统的导航、定位、授时等功能外,可免费提供全球覆盖、高时间分辨率的L波段(1—2 GHz)微波信号用于遥感探测。继GNSS折射信号被率先用于地震、大气水汽等的探测以来,利用GNSS反射信号进行海洋、陆表参数估算,近年来成为国际GNSS应用研究前沿热点。随着中国自主北斗导航系统的蓬勃发展,将会为GNSS遥感带来新的发展契机和空间。本文从GNSS遥感的两个重要学科分支,即GNSS折射信号遥感(GNSS refractometry)和GNSS反射信号遥感GNSS-R(GNSS Reflectometry),回顾在这一交叉学科领域近几十年的发展,并简要分析GNSS遥感发展面临的机遇与挑战。     

TopconNET—G3 GNSS接收机试验结果及其分析

在简述Topcon NET—G3 GNSS接收机特点的基础上，对Topcon NET—G3GNSS接收机进行了检测，获得了试验结果，得出了这种仪器在精度上能满足GNSS连续运行站技术要求等一些重要结论。