Table of Content

31 December 2018, Volume 47 Issue S0

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The Calculation Method and Performance Evaluation on SISA of New Generation BDS

CHEN Jinping, CAO Yueling, GUO Rui, LI Xiaojie, MENG Xin

2018, 47(S0):  1-8.  doi:10.11947/j.AGCS.2018.20180316

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Integrity is an important indicator of the reliability of satellite navigation systems. Improving the integrity service is an important part of BDS global navigation system construction.This paper presents a SISA (signal in space accuracy) calculation algorithm with variance conversion prediction based on apriori precision adjustment, and the performance of the SISA for error envelopment is evaluated based on the real data of new generation BeiDou navigation system.SISA_oe is verified by the precision orbit overlap error in orbital plane, and the SISA_oc is verified by the orbital radial overlap error, SLR check error and clock error estimated by the two-way time-frequency transmission.The results show that the error envelope performance of the SISA_oe parameter for orbital plane error is 99.6%;the error envelope performance of the SISA_oc parameter for the track radial and clock error is 98.5%, and for the SLR check error is 99.5%.

FY3C Satellite Onboard BDS and GPS Data Quality Evaluation and Precise Orbit Determination

LI Wenwen, LI Min, ZHAO Qile, SHI Chuang, GUO Xiang, MENG Xiangguang, YANG Zhongdong

2018, 47(S0):  9-17.  doi:10.11947/j.AGCS.2018.20180282

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To analyze the precise orbit determination (POD) performance with combined onboard GPS and BDS data, we collect one-month worthy of BDS and GPS dual-frequency data from FY3C satellite during May 2015. The onboard BDS and GPS data quantity and quality are evaluated. It is revealed that there are over 98% epochs with 4 or more GPS satellites available, but only 35% epoch can observed 4 or more BDS satellites. Similar with the ground BDS data, the code-carrier divergences are also found in the onboard FY3C BDS data with fluctuations exceeding 1 m. However, these multipath error variations are observed not only related to elevations and frequencies but also to azimuths. The POD precision with only GPS data is evaluated by overlap comparison, showing good orbit consistency at 20 mm level (3D RMS). We perform the combined POD with three different strategies. It is shown that it can dramatically degrade the POD precision when BDS GEO (geosynchronous orbit satellites) observations are involved and treated with equal weighting, and the orbit precision is about 90 mm level compared to the GPS-only orbits. This should be attributed to the degraded BDS GEO satellite orbit and clock products. However, when performing combined POD with only BDS IGSO and MEO satellites along with GPS or by reducing the weights of GEO observations, the post-fit RMS of BDS LC residuals are comparable to that of GPS, and the orbit differences between combined POD and GPS-only POD are only at 10 mm level. This indicates that the precisions of combined POD using these two strategies are very consistent with respect to POD with GPS data alone.

Precise Orbit Determination for the BDS IGSO Satellites Under the Yaw-steering Mode

GUO Rui, ZHOU Jianhua, HU Xiaogong, LI Xiaojie, LIU Li, ZHOU Shanshi, WU Shan

2018, 47(S0):  18-27.  doi:10.11947/j.AGCS.2018.20180286

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Considering the energy supply and security factors, both the orbit-normal mode and the yaw-steering mode are adopted in the BDS IGSO attitude control system. The irradiation instances for the satellite body and solar panel are different for the two attitude control mode, with different dynamic models. If using the ordinary dynamic models in the precise orbit determination (POD), the POD accuracy declines seriously during the yaw-steering period. Therefore the average availability falls 2% in the BDS key service area, and 4% in the BDS total service area, the service performance faces serious challenges. A new POD strategy is brought forward with the restriction of time offsets in this paper for the BDS IGSO satellites during the yaw-steering period. The time offsets application strategy, systematic error controlling strategy, and dynamic models errors compensation strategy are designed in this paper in order to solve the BDS IGSO POD accuracy falling problem. The IGSO satellites ephemeris is consecutive for the transformations between the orbit-normal mode and the yaw-steering mode. The BDS navigation service is consecutive, with the continuous and steady space signal accuracy for the IGSO satellites. POD experiments were carried out during the BDS IGSO yaw-steering period. Results showed that the user equivalent ranging error (UERE) is improved from 2.95 m to 1.22 m for the BDS C06 satellite, and from 6.29 m to 1.54 m for the BDS C09 satellite. The ratio of UERE less than 2.5 m is improved from 59.87% to 94.85% for the C06 satellite, and from 35.04% to 88.49% for the C09 satellite. And the ratio of UERE less than 5 m is improved from 92.10% to 99.98%for the C06 satellite, and from 71.67% to 99.43% for the C09 satellite.

An Efficient Algorithm with Reduced Dynamic Orbit Determination for LEOs Based on Parameter Transforming

YAN Zhichuang, XU Xinqiang, ZHAO Dejun, ZHANG Yingli, LOU Nan

2018, 47(S0):  28-37.  doi:10.11947/j.AGCS.2018.20180307

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Aimed at the problem that the efficiency of reduced dynamic orbit determination(OD) for LEOs became lower and lower as the piece-wise dynamic parameters increased, an efficient algorithm, which was based on parameter transforming was proposed and a set of formulas were deduced theoretically. Using the efficient algorithm, the LEOs' OD was realized and the performance was improved efficiently. An experiment that nine parameters' empirical force model and pseudo stochastic pulse model were used to smooth GRACE-B's precise orbit respectively was performed. The result shows that the RMS in R, T and N is less than 0.004 m. In the way of efficiency, the improvement of nine parameters' empirical force model is not distinct, but compared to the traditional algorithm, the time consumed by the efficient algorithm is saved about 69%. Another reduced dynamic OD experiment is performed by using nine parameters' empirical force model and pseudo stochastic pulse model. The result shows that the RMS in R, T and N reachs 0.02 m. In the way of efficiency, compared to the traditional algorithm, the time consumed is saved about 21% in the former and 78% in the latter by the efficient algorithm.

Detection and Repair of the Non-significant Cycle Slip in BDS Triple-frequencies GIF Combination

ZHANG Chenxi, DANG Yamin, XUE Shuqiang, ZHANG Longping

2018, 47(S0):  38-44.  doi:10.11947/j.AGCS.2018.20180314

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The accuracy of BDS triple-frequency cycle slip detection and repair is influenced by the observation environment. Three linear independence geometry-free and ionosphere-free combinations (GIF) have been widely applied detect and then to repair the GNSS cycle-slip, but for some special cycle-slip combinations or when observations with bad observation environment, the cycle-slip repair may be invalidated. For this, we further introduce the STPIR combination to the GIF model to detect and repair the cycle-slip, and use the second-order time-difference of the STPIR to further reduce the influence of the observational noise. The proposed method was applied to detect cycle slips in BDS observations during a magnetic storm. It shows that the proposed method can be used to detect and repair all possible cycle-slip combinations of BDS un-differenced observations.

Impact of Second Order Ionosphere Delays for GPS Kinematic Precise Point Positioning Applications

ZHANG Shaocheng, WANG Xinzhe, HUANG Longqiang, YIN Fei

2018, 47(S0):  45-53.  doi:10.11947/j.AGCS.2018.20180299

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In the GPS precise point positioning algorithms, the ionosphere delays were considered as eliminated with ionosphere-free combination. However, the IF combination can only eliminates the first order ionosphere delays and the second order ionosphere (Ion2) delays were actually enlarged. As the Ion2 can affect the observations over centimeters level, the effects on PPP positioning results may not be negligible for centimeters-accuracy applications. In this research, the impacts of Ion2 delays on kinematic precise point positioning applications were calculated with both real and simulated observations. With 21 IGS station observations, the maximum effects of Ion2 delay on positioning result are 0.8 cm on horizontal, and over 2.4 cm on vertical. On the simulation analysis, an 2.5×5 degree global grid observations were simulated with Ion2 delay, and the maximum Ion2 delay can reach up to 3 cm and cause over 7 cm bias on positioning results. Both real and simulated results show that the Ion2 delays affect the positioning results with systematic bias on south direction, which cannot be eliminated with smoothing algorithm. Hence, it concluded that the PPP cannot be neglected the second order ionosphere delays to breakthroughs the accuracy limitation on centimeters level.

GNSS Partial Ambiguity Resolution Based on Posterior Probability and Minimum Squares Error Solution

WU Zemin, BIAN Shaofeng

2018, 47(S0):  54-60.  doi:10.11947/j.AGCS.2018.20180295

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GNSS partial ambiguity resolution (PAR) is usually used in weak GNSS positioning model to gain an acceptable position solution. In order to further improve the positioning precise of PAR, this contribution modifies RAR from 3 aspects. ① Whether an element of the ambiguity vector is fixed is determined by the posterior probability instead of the Bootstrapping success rate. For the reason that posterior probability is based on data and model simultaneously, whereas Bootstrapping success rate is only determined by GNSS positioning model. ②In the ambiguity partially fixed cases, the minimum squares error (MSE) solution of unfixed elements is calculated by the correlation with other fixed ones. However, traditional PAR treats them as conditional float solutions. ③ In the ambiguity totally unfixed cases, the MSE solution of the whole ambiguity vector is used to take the place of its float solution. In the experiment, a set of BDS real observed data are used to testify the property of traditional and new PAR. The results show that the partial fixed and unfixed cases for our new PAR method are less than that for the traditional one, and the position precise is sufficiently improved.

Combined Clock Error Prediction Model and Accuracy Evaluation of BeiDou New Generation Navigation Satellite

WANG Dongxia, GUO Rui, XIE Jinshi, HU Xiaogong, YUAN Yunbin

2018, 47(S0):  61-70.  doi:10.11947/j.AGCS.2018.20180283

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The atomic clock is the core equipment of navigation satellite, and its performance and prediction accuracy directly determine the PNT accuracy. The authors evaluated the in-orbit performance and prediction accuracy on atomic clock of new generation navigation satellite using bi-directional time synchronization data. Firstly, the performance evaluation method of satellite clock is studied. The clock error data are preprocessed by the combined MAD gross error detection method. The frequency accuracy and frequency drift rate are evaluated by the least square method and polynomial function method. The frequency stability of the satellite clock is calculated and discussed by the overlapping Hadamard variance. Secondly, the weighted combined clock error prediction model is established, which synthesize the polynomial model and the gray model by the classical weighted method. Finally, the performance and prediction accuracy of the atomic clock is evaluated by using the measured data of the new generation satellites and the regional satellites. The results illustrate that the frequency accuracy, stability and prediction accuracy of the new generation satellites are improved. Moreover, the inter-satellite link increases greatly the measure arc of MEO satellite, and simultaneously improves the prediction accuracy of re-entry.

Two Improved Algorithms for LS+AR Prediction Model of the Polar Motion

JIA Song, XU Tianhe, YANG Honglei

2018, 47(S0):  71-77.  doi:10.11947/j.AGCS.2018.20180296

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The polar motion(PM) is the important parameter to represent the earth movement, and the high-precision prediction of PM plays a key role in practical applications of astronomical research, the geodetic survey, navigation, aviation, ocean sounding and interplanetary navigation. Two modified algorithms are proposed to improve the PM prediction accuracy based on combination of least square and autoregressive model (LS+AR). One is to combine Kalman filtering (KF) to improve AR model accuracy, namely LS+AR+KF algorithm. The other is to use least mean square adaptive filtering (LMSAF) to improve the accuracies of LS fitting terms and predicting extrapolations, namely LS+AR+AF algorithm. The results show that LS+AR+KF and LS+AR+AF algorithms can significantly enhance the prediction accuracy of PM especially for long-term perdition, and LS+AR+AF is obviously superior to LS+AR and LS+AR+KF for PM prediction. The accuracy improvement of PM X component, PM Y component and PM can reach about 26%, 23% and 24% respectively, when using LS+AR+AF algorithm.

Phase Center Calibration for Receiver Antenna and Its Impact on Precise Orbit Determination of BDS Satellites

SU Mudan, ZHAO Qile, GUO Jing, SU Xing, HU Zhigang, GUO Huijun

2018, 47(S0):  78-85.  doi:10.11947/j.AGCS.2018.20180324

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The phase center corrections (PCCs) for TRM57971.00/NONE and TRM59800.00/NONE antennas on GPS L1 and L2 as well as BDS B1I and B2I frequencies were calibrated by automatic robot. Additionally, the differences between calibrated PCCs of GPS L1 and L2 as well as BDS B1I and B2I were compared. Three kinds of BDS precise orbit products were determined with or without accounting for the receiver antenna's Phase Center Offsets (PCOs) or PCCs based on about 31 stations from International GNSS Service (IGS) Multi-GNSS Experiment (MGEX) network to investigate the impacts of receiver antenna on BDS orbits. The results demonstrated that the overlapping orbit differences of BDS Inclined Geosynchronous Orbit (IGSO) satellites were improved by 63.1 mm, 21.5 mm, and 6.7 mm in along-track, cross-track, and radial directions, respectively. For BDS Medium Earth Orbit (MEO) satellites, the improvements can reach to 217.1 mm, 75.8 mm, and 23.3 mm in along-track, cross-track, and radial directions, respectively, when the PCOs only have been used for precise orbit determination. And the similar performance has been achieved by using PCCs as that of using PCOs only. The accuracy of precise point positioning improved nearly 10.0 mm in up direction once the calibrated PCCs were used.

Analysis of the Impact of SLR Data on Precise Orbit Determination of BeiDou Satellites

KONG Yao, ZHANG Xiaozhen, SUN Baoqi, LIU Feng

2018, 47(S0):  86-92.  doi:10.11947/j.AGCS.2018.20180293

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Besides microwave tracking data, satellite laser ranging (SLR) tracking data of BeiDou Satellites can also be obtained. In order to improve the accuracy and consistency of precise satellite orbit product and analysis the impact of SLR to BeiDou satellite orbit, combined precise orbit determination of BeiDou satellites based on GNSS and SLR data was proposed in this paper. Combined precise orbit determination was carried out on normal equation level, and the ratio between GNSS and SLR data was 1:1. Data process was carried out using 114 MGEX stations and 26 SLR stations for BeiDou C08,C10 and C11 satellites. The results show that combined SLR data can improve the radial precision of BDS satellites. Compared with GNSS solutions, combined solution has more effect on the orbit precision of BDS MEO satellites than that of BDS IGSO satellites.

Accuracy Assessment of BDS Precision Orbit Determination and the Influence Analysis of Site Distribution

CHEN Ming, GUO Jiming, WU Junli, SONG Weiwei, ZHANG Longping

2018, 47(S0):  93-100.  doi:10.11947/j.AGCS.2018.20180278

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BDS precision orbit determination is a key content of the BDS application, and the number and distribution of reference stations are important factors affecting the accuracy of the orbit determination. In this paper, the BDS precise orbit determination results are obtained by using the IGS MGEX stations and the national reference stations in China. The accuracy of orbit determination of GEO, IGSO and MEO is 10.3 cm, 2.8 cm and 3.2 cm, and the radial accuracy is better than 2 cm.The results show that the accuracy of the overlapping arcs is increased by 17.6% after adding the national reference stations in China, and the accuracy of IGSO satellite is improved by 36.3%. The results of ODOP and SLR were further analyzed. It was found that the improvement of ODOP improved area and SLR was consistent with the accuracy of overlapping arc.

Theoretical DDM Modeling of GNSS-R Fully Polarization Land Surface Geophysical Parameters

WU Xuerui, JIN Shuanggen

2018, 47(S0):  101-108.  doi:10.11947/j.AGCS.2018.20180321

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At present, most of the existing research are based on the experimental observations, few theoretical studies have been carried out.This paper has developed a fully polarization GNSS-R delay Doppler map for land geophysical parameters study. This theoretical model was based on the ocean surface GPS scattering model. After the modifications, it has been used for the land surface. As for the calculations of land geophysical parameters (bare soil and vegetation), random surface scattering model and the first order radiation transfer equation model were used. Effects of bare soil and vegetation parameters on the delay Doppler maps were simulated. In order to use the polarization information for backward inversion, our developed theoretical model has the ability of fully polarizations calculations, i.e. RR, LR, HR and VR pol. This theoretical model is a mechanism tool for the data explanation of space borne mission, experimental campaign design, data simulations and the backward inversion algorithm development.

BDS/GPS Equal-weight Combined Carrier Phase Time Transfer Method in Occlusion Environment

YU Heli, HAO Jinming, GUO Fusheng, GUO Jiayu

2018, 47(S0):  109-116.  doi:10.11947/j.AGCS.2018.20180291

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The time transfer model is given using BDS/GPS observations, and the results of time and frequency transfer under different cut-off elevation angles are compared between BDS, GPS and BDS/GPS. Experimental results show that the performance of BDS/GPS time and frequency transfer result is not significantly improved compared to the single system when the number of available satellites is enough. However, when the cut-off elevation angle is larger than 30 degrees, the single system can't get continuous time and frequency transfer results, but the BDS/GPS combination can still obtain continuous results. Compared to single system method, both the stability and convergence time are improved. This has a very important application value in some special conditions, for instance, deep open pit mines and urban canyons when not all satellites are visible.