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An acquisition method is proposed which saves processing time and rapidly finds the Global Positioning System (GPS) satellite
with high receiving power. The idea is to combine two or more Coarse/Acquisition (C/A) codes to process acquisition, thus
called “multi-C/A code acquisition method.” The proposed method will change the procedure of conventional Fast Fourier Transform
acquisition slightly, and it has the capabilities to combine with other acquisition methods to perform signal acquisition
simultaneously. In order to show how this multi-C/A code acquisition method may improve the Time To First Fix at the cold
start, the real raw Intermediate Frequency data from a GPS software receiver are used to validate this multi-C/A code acquisition
method. The results show that this method can save at least 23% processing time and it is able to detect the satellite more
rapidly. 相似文献
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Marek Ziebart Paul Cross Antony Sibthorpe Peter Arrowsmith Washington Ochieng Shaojun Feng Umar Bhatti Peter Niemann 《GPS Solutions》2007,11(4):227-237
The Galileo integrity chain depends on a number of key factors, one of which is contamination of the signal-in-space errors
with residual errors other than imperfect modelling of satellite orbits and clocks. A potential consequence of this is that
the user protection limit is driven not by the errors associated with the imperfect orbit and clock modelling, but by the
distortions induced by noise and bias in the integrity chain. These distortions increase the minimum bias the integrity chain
can guarantee to detect, which is reflected in the user protection limit. A contributor to this distortion is the inaccuracy
associated with the estimation of the offset between the Galileo sensor station (GSS) receiver clocks and the Galileo system
time (GST). This offset is termed the receiver clock synchronization error (CSE). This paper describes the research carried
out to determine both the CSE and its associated error using GPS data as captured with the Galileo System Test Bed Version
1 (GSTB-V1). In the study we simulate open access to a time datum using IGS data. Two methods are compared for determining
CSE and the corresponding uncertainty (noise) across a global network of tracking stations. The single-epoch single-station
method is an ‘averaging’ technique that uses a single epoch of data, and is carried out at individual sensor stations, without
recourse to the data from other stations. The global network solution method is also single epoch based, but uses the inversion
of a linearised model of the global system to solve for the CSE simultaneously at all GSS along with a number of other parameters
that would otherwise be absorbed into the CSE estimate in the averaging technique. To test the effectiveness of various configurations
in the two methods the estimated synchronisation errors across the GSS network (comprising 25 stations) are compared to the
same values as estimated by the International GPS Service (IGS) using a global tracking network of around 150 stations, as
well as precise orbit and satellite clock models determined by a combination of global analysis centres. The results show
that the averaging technique is vulnerable to unmodelled errors in the satellite clock offsets from system time, leading to
receiver CSE errors in the region of 12 ns (3.7 m), this value being largely driven by the satellite CSE errors. The global
network approach is capable of delivering CSE errors at the level of 1.5 ns (46 cm) depending on the number of parameters
in the linearised model. The International GNSS Service (IGS) receiver clock estimates were used as a truth model for comparative
assessment. 相似文献
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遥感卫星的轨道外推方法 总被引:1,自引:0,他引:1
通过星载GPS接收机直接确定卫星星历是低轨卫星定位的一个重要手段。由于低轨卫星的高机动性和GPS接收机较低的运算速度,导致有时下传星历数据的间隔非常大,要荻取连续的卫星轨道数据需要进一步处理。在分析遥感卫星轨道特点的基础上,提出一种新的简化轨道摄动力模型,利用模型实现了轨道外推,并利用最小方差序列匹配对低轨卫星外推数据进行修正。通过仿真验证,该算法在一定时间范围内可以达到较高的精度。 相似文献
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GNSS接收机数据质量是接收机实现各项功能、向用户提供各项服务的基础。针对当前GNSS数据质量核验方法和评价指标较为单一,分析方法不系统的问题,文中分析一种综合利用TEQC、GAMIT、RTKLIB三款软件进行GNSS数据质量分析的方法,并给出相应质量分析指标。以北京市全球卫星定位系统网络中基准站数据为基础,对北斗三模接收机和GPS/GLONASS双模接收机数据质量进行对比分析,对比结果显示,石景山和牛口峪两个站数据质量整体较差,mp1大于0.5m,mp2大于0.75m,周跳比小于2 000。对影响数据质量的原因进行初步分析,通过实地勘测验证理论分析结果,对比分析结果表明:采用文中提出的质量分析方法所判断出的问题同实地勘察结果一致,验证本方法的实用性。最后针对基准站存在的问题向相关部门提出改善建议,并对改善后该站观测数据进行质量分析,各项指标均达标。 相似文献
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The paper presents a procedure and a software package to compute the sea surface humidity and atmospheric back radiation over
the sea from satellite data. These parameters play an important role in air-sea exchange of heat, which in turn, determines
the climate. Presently, there are no satellite sensors designed to retrieve them directly by remote sensing. This requires
us to depend onin situ data, which are relatively sparse. We present a procedure in this paper that uses emission characteristics of sea surface
in the microwave region of electro-magnetic spectrum to retrieve these parameters. A suite of computer programs developed
for the purpose are also presented in the paper with their complete source code. The procedure is based on an algorithm originally
proposed by Schlussel in 1995. We have presented results for surface humidity and back radiation over the Arabian sea for
the year 2000 and have shown them to be in agreement with the atmospheric and oceanographic processes operating during the
corresponding seasons. 相似文献
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在地-空路径传播过程中,云衰减对无线电卫星通信系统的高频率信号有着不可忽略的影响。利用HATPRO型微波辐射计观测反演获得的云中液态水密度廓线等信息,提出了一种适用于中纬度地区的精确计算云衰减的方法,得出了地-空路径信号传播过程中,云衰减对信号的影响随着频率增大急剧扩大的结论;具体表现为,在高频波段,99.99%的链路可用时间内云衰减超过10 dB。将微波辐射计计算所得的云衰减与云中液态水总量建立“线性关系”,与ITU-R(国际电联无线电通信部门)模型结果对比。结果表明:由于ITU-R模型低估了武汉地区的云中液态水总量,导致该模型低估了武汉地区的云衰减影响。 相似文献
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Estimation and analysis of Galileo differential code biases 总被引:1,自引:0,他引:1
Min Li Yunbin Yuan Ningbo Wang Zishen Li Ying Li Xingliang Huo 《Journal of Geodesy》2017,91(3):279-293
When sensing the Earth’s ionosphere using dual-frequency pseudorange observations of global navigation satellite systems (GNSS), the satellite and receiver differential code biases (DCBs) account for one of the main sources of error. For the Galileo system, limited knowledge is available about the determination and characteristic analysis of the satellite and receiver DCBs. To better understand the characteristics of satellite and receiver DCBs of Galileo, the IGGDCB (IGG, Institute of Geodesy and Geophysics, Wuhan, China) method is extended to estimate the satellite and receiver DCBs of Galileo, with the combined use of GPS and Galileo observations. The experimental data were collected from the Multi-GNSS Experiment network, covering the period of 2013–2015. The stability of both Galileo satellite and receiver DCBs over a time period of 36 months was thereby analyzed for the current state of the Galileo system. Good agreement of Galileo satellite DCBs is found between the IGGDCB-based DCB estimates and those from the German Aerospace Center (DLR), at the level of 0.22 ns. Moreover, high-level stability of the Galileo satellite DCB estimates is obtained over the selected time span (less than 0.25 ns in terms of standard deviation) by both IGGDCB and DLR algorithms. The Galileo receiver DCB estimates are also relatively stable for the case in which the receiver hardware device stays unchanged. It can also be concluded that the receiver DCB estimates are rather sensitive to the change of the firmware version and that the receiver antenna type has no great impact on receiver DCBs. 相似文献
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Due to their low cost and low power consumption, single-frequency GPS receivers are considered suitable for low-cost space applications such as small satellite missions. Recently, requirements have emerged for real-time accurate orbit determination at sub-meter level in order to carry out onboard geocoding of high-resolution imagery, open-loop operation of altimeters and radio occultation. This study proposes an improved real-time kinematic positioning method for LEO satellites using single-frequency receivers. The C/A code and L1 phase are combined to eliminate ionospheric effects. The epoch-differenced carrier phase measurements are utilized to acquire receiver position changes which are further used to smooth the absolute positions. A kinematic Kalman filter is developed to implement kinematic orbit determination. Actual flight data from China’s small satellite SJ-9A are used to test the navigation performance. Results show that the proposed method outperforms traditional kinematic positioning method in terms of accuracy. A 3D position accuracy of 0.72 and 0.79 m has been achieved using the predicted portion of IGS ultra-rapid products and broadcast ephemerides, respectively. 相似文献
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A low-complexity time-domain approach for global navigation satellite systems is proposed to detect and identify single-tone, multi-tone, swept continuous wave interference (CWI) and band-limited white Gaussian noise (BLWN). An adaptive notch filter and adaptive cascading filter structure are employed to identify the type of interference signals. The number of the cascading stages is selected by comparing the total power in receiver bandpass, and after, passing the adaptive notch filter. For this reason, the proposed filter structure is more efficient in identifying and mitigating interference signals than the conventional filter structure. In addition, the automatic gain control gain is used to detect the existence of continuous wave interference. The performance of the interference detection and identification method is evaluated for the cases of GPS signal in the presence of single-tone, multi-tone, swept CWI and BLWN. 相似文献
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The Bayesian detection of discontinuities in a polynomial regression and its application to the cycle-slip problem 总被引:4,自引:1,他引:3
Maria Clara de Lacy Mirko Reguzzoni Fernando Sansò Giovanna Venuti 《Journal of Geodesy》2008,82(9):527-542
This paper deals with the problem of detecting and correcting cycle-slips in Global Navigation Satellite System (GNSS) phase
data by exploiting the Bayesian theory. The method is here applied to undifferenced observations, because repairing cycle-slips
already at this stage could be a useful pre-processing tool, especially for a network of permanent GNSS stations. If a dual
frequency receiver is available, the cycle-slips can be easily detected by combining two phase observations or phase and range
observations from a single satellite to a single receiver. These combinations, expressed in a distance unit form, are completely
free from the geometry and depend only on the ionospheric effect, on the electronic biases and on the initial integer ambiguities;
since these terms are expected to be smooth in time, at least in a short period, a cycle-slip in one or both the two carriers
can be modelled as a discontinuity in a polynomial regression. The proposed method consists in applying the Bayesian theory
to compute the marginal posterior distribution of the discontinuity epoch and to detect it as a maximum a posteriori (MAP)
in a very accurate way. Concerning the cycle-slip correction, a couple of simultaneous integer slips in the two carriers is
chosen by maximazing the conditional posterior distribution of the discontinuity amplitude given the detected epoch. Numerical
experiments on simulated and real data show that the discontinuities with an amplitude 2 or 3 times larger than the noise
standard deviation are successfully identified. This means that the Bayesian approach is able to detect and correct cycle-slips
using undifferenced GNSS observations even if the slip occurs by one cycle. A comparison with the scientific software BERNESE
5.0 confirms the good performance of the proposed method, especially when data sampled at high frequency (e.g. every 1 s or
every 5 s) are available. 相似文献
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Paul A. Bernhardt Carl L. Siefring Ivan J. Galysh Thomas F. Rodilosso Douglas E. Koch Thomas L. MacDonald Matthew R. Wilkens G. Paul Landis 《Journal of Geodesy》2006,80(8-11):473-485
The scintillation and tomography receiver in space (CITRIS) instrument will orbit the Earth near 560 km altitude to detect signals from the ground-based array of more than 50 DORIS UHF/S-band radio beacons established at sites around the world by the French Centre National d‘Etudes Spatiales (CNES) and the Institut Géographique National (IGN). The CITRIS receiver is on the US Air Force Space Test Program satellite STPSAT1, which is scheduled for launch in November 2006. CITRIS will record ionospheric total electron content (TEC) and radio scintillations with a unique ground-to-space geometry. The new instrument has been developed to study the ionosphere using data obtained with the UHF and S-band radio transmissions from the DORIS beacons because ionospheric radio scintillations can seriously degrade the performance of many space-geodetic systems, including the DORIS precise satellite orbitography system and GNSS (Global Navigation Satellite Systems). The ionospheric data will be based on radio signals sampled at a rate of 200 Hz by the CITRIS receiver. Numerical models have been used to predict that the DORIS signals measured by CITRIS may have 30 dB fluctuations in amplitude and 30 rad in phase as the satellite flies over kilometer-scale ionospheric structures. The data from the space-based CITRIS receiver will help update and validate theories on the generation and effect of ionospheric irregularities known to influence radio systems. By using simultaneous beacon transmissions from DORIS on the ground and from low-Earth-orbit beacons in space, the concept of reciprocity in a non-bilateral propagation medium like the ionosphere will be tested. Computer simulations are used to predict the magnitude of amplitude and phase scintillations that are expected to be recorded with the CITRIS instrument. 相似文献
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Reshu Agarwal Rakesh Gupta J. K. Garg 《Journal of the Indian Society of Remote Sensing》2009,37(3):473-481
A three-step hierarchical Semi Automated Empirical Methane Emission Model (SEMEM) has been used to estimate methane emission
from wetlands and waterlogged areas in India using Moderate Resolution Imagine Spectroradiometer (MODIS) sensor data onboard
Terra satellite. Wetland Surface Temperature (WST), methane emission fluxes and wetland extent have been incorporated as parameters
in order to model the methane emission. Analysis of monthly MODIS data covering the whole of India from November 2004 to April
2006 was carried out and monthly methane emissions have been estimated. Interpolation techniques were adopted to fill the
data gaps due to cloudy conditions during the monsoon period. AutoRegressive Integrated Moving Average (ARIMA) model has been
fitted to estimate the emitted methane for the months of May 2006 to August 2006 using SPSS software. 相似文献
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中国风云3号B星(FY-3B)上的微波成像仪MWRI通过5个频率(10.65 GHz,18.7 GHz,23.8 GHz,36.5 GHz和89.0 GHz)的双极化通道对地球表面进行监测。研究表明,MWRI资料的低频波段数据中存在着无线电频率干扰(RFI)现象,这些污染信号对遥感数据和反演产品质量产生极大的影响。本文尝试使用多通道回归方法和双主成分分析(DPCA)方法识别MWRI的10.65 GHz水平通道亮温海洋区域中的RFI信号。结果表明,双主成分分析法可以有效地识别出海洋上的RFI信号。微波成像仪10.65 GHz水平通道亮温数据中的RFI信号主要分布在地中海等欧洲附近海域,也存在于美国、日本、澳大利亚等近岸地区。 相似文献
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《Geoscience and Remote Sensing Letters, IEEE》2009,6(4):625-629
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为了获取高精度的客机位置数据,本文将手持GNSS接收机带上客机,在飞机飞行过程中接收卫星数据,然后利用专用网络事后差分系统对接收到的GNSS数据进行事后差分。由于手持GNSS接收机放置在客机玄窗旁,只能接收到半边天的卫星数据,因此需要对事后差分算法进行优化。将优化后的结果与地面RTK差分结果进行比较结果表明:利用本文算法可以达到分米级高精度定位的效果。 相似文献
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针对星载接收平台提出了一种利用全球导航卫星系统反射信号(Global Navigation Satellite Systemreflectometry,GNSS-R)进行海冰边界探测的方法。该方法利用导航卫星信号经海冰和海水表面散射后反射信号时延相关功率映射(delay map,DM)的差异,结合镜面反射点位置来探测海冰边界。利用自适应阈值调整算法处理TDS-1卫星数据,获取有效的DM数据,进而得到DM衍生量随镜面反射点位置的变化趋势,并设置DM衍生量的阈值来识别海冰。与全球海冰分布图对比发现,DM衍生量阈值对应的镜面反射点位置与海冰分布图的海冰边界位置基本吻合,证明了DM的有效区时延距离、相关功率的峰值和归一化标准差均可用于海冰边界探测,星载GNSS-R技术在海冰边界探测领域具有较大潜力。 相似文献