AbstractThe BeiDou Navigation Satellite System (BDS) has used the BeiDou Coordinate System (BDCS) as its geodetic reference system since December 2017. After a brief description of the background, ...definitions of the origin, scale, and orientation of BDCS are given, which are consistent with China’s Geodetic Coordinate System 2000 (CGCS2000). Then the first realization of the BDCS aligning with the International Terrestrial Reference Frame 2014 (ITRF2014) is addressed. Coordinates at epoch 2018.0 and velocities at eight BDS monitoring stations were obtained achieved by processing four-phase GPS data for a global navigation satellite system (GNSS) network, including the monitoring stations, and by the frame alignment and linear regression fitting of station coordinate series. Assessment of the precision of the coordinates and Helmert parameters with respect to ITRF2014 reveals that the differences between the first frame of BDCS and ITRF2014 are less than 1 cm, which is compatible with WGS84 (G1762), PZ-90.11, and the latest Galileo terrestrial reference frame.
The Global Navigation Satellite System Reflectometry (GNSS-R) technique can measure ocean surface winds and other geophysical parameters from forward scattered Global Navigation Satellite System ...(GNSS) (Global Positioning System (GPS), BeiDou (BDS), Galileo, etc.) signals. However, most early spaceborne missions only captured GPS signals while the study of spaceborne BDS reflectometry (BDS-R) is limited. The Global Navigation Satellite System Occultation Sounder II (GNOS-II) payload onboard China's FY-3E satellite has been operationally collecting a large number of BDS-R data since July 10, 2021. BDS is different from GPS in the orbit, signal frequency, chipping rate, and effective isotropic radiated power (EIRP). Furthermore, the BDS satellites have different generations and orbits. This article, for the first time, comprehensively characterizes the spaceborne BDS-R observations over the ocean using the FY-3E GNOS-II data from different BDS satellite types including BDS-2 inclined geosynchronous orbit (IGSO), BDS-2 medium Earth orbit (MEO), BDS-3 IGSO, and BDS-3 MEO. Their spatial coverage, spatial resolution, effective scattering area (ESA), incidence angle, range corrected gain (RCG), EIRP, and signal-to-noise ratio (SNR) have been analyzed and compared with those of GPS-R. Spaceborne BDS-R shows a lot of uniquenesses compared with GPS-R. The BDS-R observables are then calibrated separately for each type. An intercalibration is also applied to correct extra calibration errors. After calibration, BDS-R observables and retrieved winds are consistent between each type and compared with those of GPS-R. Calibrated observables from FY-3E GNOS-II are also evaluated by comparing them to those measured by the Cyclone GNSS (CYGNSS) mission and a theoretical model. The results of this article can provide a reference for future BDS-R studies and spaceborne GNSS-R mission design.
•Evaluated the advantages of the reconstructed method for BDS3 IFCB estimation.•Analyzed the characteristics of BDS3 multi-frequency IFCB variations.•Proposed a real-time forecasting service for BDS3 ...multi-frequency IFCB in PPP.
BDS-3 broadcasts five civilian signals, establishing a fundamental basis for multi-frequency real-time precise point positioning (RT PPP). Nevertheless, the existence of inter-frequency clock bias (IFCB) renders the current satellite clock error product unsuitable for multi-frequency PPP processing. Consequently, there is a critical need to conduct a thorough analysis of BDS-3 IFCBs and propose real-time service methods for RT PPP users. In this study, 8-day BDS-3 multi-frequency data obtained from 130 International GNSS Service (IGS) stations are employed to scrutinize the characteristics of BDS-3 IFCBs and validate the proposed real-time service method. The results disclose a noticeable disparity between the constant part of IFCBs computed using the differential code bias (DCB) product and those estimated from observations. The time-varying parts of different IFCBs, estimated using various combinations, are examined using the Fast Fourier Transform (FFT). The outcomes indicate that these IFCBs exhibit identical periods of 12, 6, and 4 h, although their fourth-period terms differ. To model the sequences of IFCBs, a polynomial with a fourth-order harmonic model is utilized, and the coefficients of the fitted model are subsequently transmitted for RT PPP processing. Experimental results show that the predicted accuracies of IFCBs for most satellites exceed 90 %, albeit with a noticeable decline as the prediction time increases. When applied in RT PPP for 20 IGS stations, the method significantly shortens the convergence time in dual-frequency and triple-frequency RT PPP when predicted IFCBs are provided. In the B1C/B2a, B1C/B3I, and B1I/B2a dual-frequency combinations, the average convergence times for RT PPP are reduced by 58 %, 46 %, and 59 %, respectively. In the B1I/B2a/B3I triple-frequency combinations, it is reduced by 48 %.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Ionospheric scintillation affects the tracking performance of GNSS code delay lock loop (DLL) and phase lock loop (PLL), thus degrading GNSS precise positioning accuracy. To investigate the BDS-3 ...signal tracking error characteristic under ionospheric scintillation, this study comprehensively analyzes the standard deviation of tracking error of DLL (σ DLL ) and PLL (σ PLL ) for BDS-3 B1I signal by using the data (from July 15, 2021 to August 9, 2022) collected by a newly ionospheric scintillation monitoring receiver (ISMR) station installed with the Septentrio PolaRx5S GNSS receiver at Le Dong of China (18.4°N, 108.9°E; geomagnetic latitude: 11.6°N). The analysis suggests that under scintillation activity, the σ DLL and σ PLL points of BDS-3 B1I show more stable and concentrated distribution than these of GPS L1C/A, GLONASS G1C/A, and Galileo E1C. Statistics indicate that the average values of σ DLL for BDS-3 B1I, GPS L1C/A, GLONASS G1C/A, and Galileo E1C are 0.089 m, 0.117 m, 0.100 m, and 0.126 m, and these of σ PLL are 0.563 mm, 0.732 mm, 0.623 mm, and 0.789 mm, respectively. Furthermore, based on σ DLL and σ PLL of BDS-3 B1I, the receiver tracking error stochastic (RTES) model for BDS-3 B1I precise point positioning (PPP) is established in this study. The root-mean-square (RMS) statistics show that compared with the elevation angle stochastic (EAS) model, the RTES model can improve BDS-3 single-frequency PPP by approximately 32.0%, 23.5%, and 24.3% in September-October of 2021 and by 33.2%, 31.8%, and 31.8% in March-April of 2022 in the east, north, and up directions, respectively.
A Global Satellite Navigation System (GNSS) cannot provide normal location services in an indoor environment because the signals are blocked by buildings. The Beidou satellite navigation system ...(BDS)/GPS indoor array pseudolite system is proposed to overcome the problems of indoor positioning with conventional pseudolite, such as time synchronization, ambiguity resolution and base stations. At the same time, an algorithm for Doppler differential positioning is proposed to improve the indoor positioning accuracy and the positioning coverage of the system, which uses the Doppler difference equation and Known Point Initialization (KPI) to determinate the velocity and position of the receiver. Experiments were conducted to verify the proposed system under different conditions; the average positioning error of the Doppler differential positioning algorithm was 7.86 mm in the kinematic test and 2.9 mm in the static test. The results show that BDS/GPS indoor array pseudolite system has the potential to make indoor positioning achieve sub-centimeter precision. Finally, the positioning error of the proposed algorithm is also analyzed, and the data tests show that the dilution of precision (DOP) and cycle- slips have a significant impact on the indoor positioning accuracy; a cycle-slip of a half-wavelength can cause positioning errors of tens of millimeters. Therefore, the Doppler-aided cycle-slip detection method (DACS) is proposed to detect cycle-slips of one cycle or greater than one, and the carrier phase double difference cycle-slip detection method (CPDD) is used to detect cycle slips of a half-wavelength.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Chinese Beidou satellite navigation system constellation currently consists of eight Beidou satellites and can provide prelimi- nary service of navigation and positioning in the Asia-Pacific Region. ...Based on the self-developed software Position And Navigation Data Analysis（PANDA） and Beidou Experimental Tracking Stations （BETS）, which are built by Wuhan University, the study of Beidou precise orbit determination, static precise point positioning （PPP）, and high precision relative positioning, and differential positioning are carried out comprehensively. Results show that the radial precision of the Beidou satellite orbit determination is better than 10 centimeters. The RMS of static PPP can reach several centimeters to even millimeters for base- line relative positioning. The precision of kinematic pseudo-range differential positioning and RTK mode positioning are 2-4 m and 5-10 cm respectively, which are close to the level of GPS precise positioning. Research in this paper verifies that, with support of ground reference station network, Beidou satellite navigation system can provide precise positioning from several decimeters to meters in the wide area and several centimeters in the regional area. These promising results would be helpful for the implementation and applications of Beidou satellite navigation system.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The feasibility of using China's Beidou Navigation Satellite System (BDS) signal-to-noise ratio (SNR) data for estimating soil moisture is demonstrated in this letter. Previous studies for the Global ...Navigation Satellite System (GNSS) multipath for estimating soil moisture have concentrated on the Global Positioning System (GPS) SNR data. The SNR data recorded by BDS receivers can also be strongly impacted by the relative permittivity, which however, has not been comprehensively investigated. This letter used a commercially available geodetic-quality BDS/GPS receiver to collect BDS SNR data on both B1 and B2 frequencies. Two methods were investigated to demonstrate the relationship between BDS SNR metrics and soil moisture. One was the phase method proposed by Larson et al., and the other was an interference model proposed by Peng et al. The results show that both B1 and B2 frequencies perform well to reflect the moisture fluctuations, particularly for reflecting big precipitation events. Comparisons between BDS B1 and B2 with GPS L2C and L5 demonstrate the results from these two constellations are comparable. BDS could be a new data source for producing global high-temporal soil moisture products using GNSS-based approaches.
Ultra-fast satellite clock bias (SCB) products play an important role in real-time precise point positioning. Considering the low accuracy of ultra-fast SCB, which is unable to meet the requirements ...of precise point position, in this paper, we propose a sparrow search algorithm to optimize the extreme learning machine (SSA-ELM) algorithm in order to improve the performance of SCB prediction in the Beidou satellite navigation system (BDS). By using the sparrow search algorithm's strong global search and fast convergence ability, we further improve the prediction accuracy of SCB of the extreme learning machine. This study uses ultra-fast SCB data from the international GNSS monitoring assessment system (iGMAS) to perform experiments. First, the second difference method is used to evaluate the accuracy and stability of the used data, demonstrating that the accuracy between observed data (ISUO) and predicted data (ISUP) of the ultra-fast clock (ISU) products is optimal. Moreover, the accuracy and stability of the new rubidium (Rb-II) clock and hydrogen (PHM) clock onboard BDS-3 are superior to those of BDS-2, and the choice of different reference clocks affects the accuracy of SCB. Then, SSA-ELM, quadratic polynomial (QP), and a grey model (GM) are used for SCB prediction, and the results are compared with ISUP data. The results show that when predicting 3 and 6 h based on 12 h of SCB data, the SSA-ELM model improves the prediction model by ~60.42%, 5.46%, and 57.59% and 72.27%, 44.65%, and 62.96% as compared with the ISUP, QP, and GM models, respectively. When predicting 6 h based on 12 h of SCB data, the SSA-ELM model improves the prediction model by ~53.16% and 52.09% and by 40.66% and 46.38% compared to the QP and GM models, respectively. Finally, multiday data are used for 6 h SCB prediction. The results show that the SSA-ELM model improves the prediction model by more than 25% compared to the ISUP, QP, and GM models. In addition, the prediction accuracy of the BDS-3 satellite is better than that of the BDS-2 satellite.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
It is well known that the ionospheric electron densities in the F‐region usually undergo day‐to‐day variability with the magnitude of ~20–35%, associated with the solar as well as geomagnetic ...activities and the meteorological forcing from the lower atmosphere. In this study, we reported remarkable enhancements in the total electron content (TEC) from the Beidou geostationary (GEO) satellites during the quiescent geophysical condition of January 2017 prior to the arrival of the sudden stratosphere warming (SSW). The daytime TEC around the equatorial ionization anomaly region increased by 75–160% and lasted for several days. The equatorial electrojet and Sq current in the ionospheric E‐region at low and middle latitudes showed the corresponding increase during the TEC enhancement interval. The possible contributions from the variations of solar EUV flux and geomagnetic activity are ruled out. Our further analysis showed that the diurnal tides in the temperature from Sounding of the Atmosphere using Broadband Emission Radiometry and the solar and lunar semidiurnal tides of neutral winds from two radars over China became strong during this period of interest. These results suggest that the lower atmospheric tidal forcing could contribute to the great and long‐duration TEC enhancement in the ionosphere even though the SSW had not happened yet.
Key Points
The abnormal ionospheric enhancements during the quiescent period were observed by the Beidou GEO TEC
Daytime TEC enhancements reached a magnitude of 75–160% around the EIA region and lasted many days
The meteorological forcing could produce such great ionospheric changes before the SSW arrival
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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