With the support of inter-satellite link technology, GNSS can theoretically achieve the distributed autonomous orbit determination (AOD) function. Traditional AOD operation generally utilizes the ...forecast ephemeris uploaded by operational control segment (OCS) as the filter reference orbits or to constrain the orbit systematic errors, especially for constellation overall rotation effects in Earth-centered inertial (ECI) coordinate system. To get rid of the dependency on forecast trajectories for saving the OCS workload and also reduce the onboard storage and computation burden, we use a sequential extended Kalman filter to estimate the orbit parameters and consider main perturbation forces acting on satellites in the AOD solution. In particular, for modeling solar radiation pressure (SRP), an empirical prediction function derived by historical SRP estimates is introduced. Using the proposed scheme, the orbit 3D accuracy and user range error (URE) of the first 180-day distributed AOD solution for BeiDou-3 MEOs with precise Earth rotation parameters (ERPs) can reach about 2.10 and 0.43 m, respectively. The constellation rotation errors implied in AOD orbits around the
X
-,
Y
- and
Z
-axis of ECI system are less than 15.0, 11.7 and 15.2 mas, respectively. For real-world AOD scenarios, precise ERP is not available for satellites. With the 180-day prediction ERP, the orbit 3D errors and URE due to the gradually increased UT1-UTC error can be elevated to 14.62 and 2.91 m during our AOD experiments. Result analysis shows if OCS can upload latest prediction ERP at a frequency of once a week, the 180-day distributed AOD is expected to consistently produce real-time orbits preferable to broadcast ephemeris derived by the traditional region L-band tracking network.
Full text
Available for:
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
Based on a global GNSS tracking network, the B1I/B3I ionospheric-free phase center offsets (PCOs) are estimated for BeiDou Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) ...satellites. Peak-to-peak variations of up to several decimeters or even meters that depend on the solar radiation pressure (SRP) model and the sun elevation angle above the orbital plane (
β
angle) are found in the daily
x
-offset estimates. Different SRP modeling has a negligible effect on the
y
-offset estimation, but the scatter of
y
-offset estimates depends on the
β
angle. The
z
-offset estimates do neither exhibit a dependence on the SRP model nor the
β
angle, but they have a larger scatter than
x
-offset and
y
-offset estimates. By comparing the performance of different SRP models in the estimation of BeiDou PCOs, the SRP models suitable for the estimation of BeiDou-2 and BeiDou-3 PCOs are determined to solve final PCOs. The BeiDou satellite PCO estimates are compared with the model values currently used within the International GNSS Service, the manufacturer values published by the Test and Assessment Research Center of China Satellite Navigation Office, and a set of BeiDou-3 MEO PCO estimates previously reported by the Chang’an University. Finally, it is demonstrated that the orbit quality of BeiDou IGSO/MEOs and the accuracy of station coordinates obtained from BeiDou-only precise point positioning benefit from the newly estimated BeiDou PCO model.
Full text
Available for:
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
Satellite attitudes that relate to the satellite antenna phase center and wind-up are essential to high-precision Global Navigation Satellite System (GNSS) data processing. However, during eclipse ...seasons, various attitude strategies are adopted in the different Multi-GNSS Experiment Analysis Centers (MGEX ACs), which may cause inconsistent yaw attitude errors between the network and user ends. Thus, exchanging satellite attitude quaternions are provided by the Centre National d’Etudes Spatiales and Collecte Localisation Satellites (CNES/CLS) to match the corresponding orbit and clock products. In this research, the yaw angle computation method that uses attitude quaternions is given, and the characteristic of the CNES/CLS attitude model is also described in the eclipse seasons. Experiments with CNES/CLS final orbit and clock products are processed to investigate the benefit of attitude quaternions on satellite clock estimation and precise point positioning (PPP). The results demonstrate that the differences between nominal and quaternion yaw angles can reach 360°. Compared with the nominal attitude, the statistic standard deviation (STD) of the clock difference can be reduced by approximately 70% with the attitude quaternions. Regarding kinematic PPP with nominal attitude, a large impact of approximately 20 cm can be found in the position biases. When applying the attitude quaternions, the root mean square (RMS) of the position biases can be significantly reduced and shows an approximately 29% improvement in the up (U) component. Furthermore, if the specific MGEX AC does not provide the attitude quaternions, deleting the eclipsing satellite can obtain a similar position accuracy to that of attitude quaternions strategy when the satellite geometry is strong. However, under the condition of few redundant observations, such as Galileo-only PPP, position performance of attitude quaternions strategy outperforms that of deleting strategy. Therefore, it is hoped that more ACs can provide attitude quaternions to match with corresponding orbit and clock products.
Full text
Available for:
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
By the end of 2016, the Galileo constellation had 4 in-orbit validation (IOV) satellites and 14 full operational capability (FOC) satellites, 17 of which were able to transmit signal in November ...2017. Galileo has already had early operational capability (EOC). To assess the latest performance of the Galileo-only precise point positioning (PPP) and the contribution of Galileo to the Multi-GNSS PPP solutions, observations collected at 16 Multi-GNSS Experiment (MGEX) stations over ten days are used to realize the various PPP cases. The statistical results show that the three-dimensional positioning accuracy of Galileo static and kinematic PPP can reach centimeter level and decimeter level after convergence, respectively. The contribution of Galileo can improve the positioning accuracy by 29.49%, 29.96% and 23.70% for GPS kinematic PPP and 11.03%, 10.59% and 11.07% for GPS/GLONASS kinematic PPP solutions in the north, east and up components, respectively. The average convergence time can be reduced by 45.48% for GPS-only kinematic PPP and by 11.04% for GPS/GLONASS solutions by adding Galileo observations. Moreover, adding Galileo observations shortens the average convergence time by 30.45% and 7.8% for GPS-only and GPS/GLONASS static PPP solutions, respectively. Although the convergent positioning results of GPS and GPS/GLONASS static PPP solutions after the addition of Galileo measurements do not demonstrate as significant improvement as those of the kinematic PPP solutions, the positioning accuracy of the GPS/Galileo static PPP solutions compared to the GPS-only static PPP still demonstrates an improvement of approximately 25% on the east component. Furthermore, the GPS/Galileo internal system time bias (ISB) and observation residual are analyzed. The results show that the noise level of the GPS L1/L2 signals and the negative impact of multipath errors on the GPS pseudo-range observations for the L1/L2 signals are greater than those of Galileo E1/E5a signals, resulting in the residuals of GPS ionosphere-free code observations larger than those of Galileo code observations. However, the phase observation residuals of GPS and Galileo are of the same magnitude. Additionally, the one-day GPS/Galileo ISB is quite stable. Its stability described by standard deviation is approximately 0.34 ns.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study comprehensively evaluated the signal-in-space range errors (SISREs) and investigated the systematic error characteristics for GPS and BDS broadcast ephemeris. The analysis reveals that on ...March 28, 2021, the satellite antenna model used by GPS ground operation centre to generate GPS II series navigation ephemeris changed from the manufacturer model to the International GNSS Service (IGS) model. This transition is carefully considered in our GPS SISRE evaluation. Experimental statistics indicate that the SISRE for GPS IIR, IIF, and III satellites is approximately 0.50, 0.46, and 0.34 m, respectively, with a value of 0.44 m for the overall constellation. With enhancements in inter-satellite links, BDS-3 GEO, IGSO, and MEO satellites exhibit SISRE of 1.20, 0.62, and 0.46 m, respectively, representing improvements of 14.3, 27.5 and 48.8 % over their BDS-2 counterparts. The ephemeris performance of BDS-3 MEOs is comparable to GPS. However, the BDS orbit quality significantly degrades over a 3-day period following manoeuvre operations and during eclipse seasons. Furthermore, the systematic error characteristics of broadcast ephemeris are analysed based on satellite laser ranging (SLR) checks and Helmert transformation. The SLR residuals of nearly all of the BDS-2/3 satellites tracked by the International Laser Ranging Service vary linearly with the Sun elongation angle. Moreover, the Z-geocentre component of the GPS/BDS orbit-realises frame exhibits obvious annual periodicity. These indicate that the GPS/BDS broadcast orbit models need further improvement. Compared with GPS, the BDS broadcast orbit-realised frame can better maintain the X- and Y-geocentric components but presents significant systematic scale bias and rotation errors. These errors for BDS are attributable to the inconsistency in the radial disturbance models between broadcast and Multi-GNSS Experiment precise orbits as well as prediction errors of the Earth rotation parameter used. The overall SLR residual mean for BDS-3 CAST and SECM MEOs are approximately 7.8 and −4.7 cm, respectively, with a standard deviation of approximately 9.9 cm, 3–4 times better than that of the BDS-2 satellites. The SLR residual dispersion of BDS-3 MEO C43 and C44 satellites is significantly larger than that of other BDS-3 MEOs, likely because of the inaccurate official coordinates of laser retroreflector arrays.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Display omitted
•ZTD retrieval performance of GPS/BDS/Galileo frequency combinations are analyzed.•Optimal frequency combination of GPS/BDS/Galileo ZTD retrieval is L1/L2, B2/B6, and E1/E7.•GNSS-ZTD ...retrieval performance is related with similarity of the used frequency.•Effect analysis of ambiguity resolution and GNSS system combination on ZTD retrieval.•GNSS-ZTD retrieval performance is affected by La Niña event.
The Global Navigation Satellite System (GNSS) is promising technology for zenith tropospheric delay (ZTD) retrieval. With the emergence of new multi-GNSS frequencies and maturity of precise point positioning ambiguity resolution (PPP-AR) technology, opportunities and challenges have arisen in high-precision GNSS-ZTD retrieval. However, certain strategies have usually been adopted, such as the traditional dual-frequency combination of American global positioning system (GPS) technology, for ZTD retrieval, but the influence of AR on ZTD retrieval has been ignored. To address this issue, in this study, the GNSS-ZTD retrieval performance of all existing dual-frequency combinations was first comprehensively evaluated by raw observations. Then, the influences of AR and system combinations were analysed with popular dual-frequency combinations. Finally, La Niña occurred during the GNSS data period considered in this article, and the effect on GNSS-ZTD retrieval was examined. The results of this study could not only provide a reference for GNSS-ZTD retrieval but also provide insight into the relationship between La Niña occurrence and GNSS-ZTD retrieval performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Satellite laser ranging (SLR) is the only stand-alone and external tool for verifying the accuracy of microwave-based GNSS orbits. On February 2, 2023, the International Laser Ranging Service ...initiated the SLR global tracking campaign for the complete BeiDou-3 medium Earth orbit (MEO) constellation. This initiative provides an opportunity to unveil the potential issue for BeiDou-3 MEO orbit modeling. An examination of the SLR validation results of precise BeiDou-3 MEO orbits across different IGS/Multi-GNSS Experiment (MGEX) analysis centres (ACs) reveals that the SLR residual standard deviation for BeiDou-3 SECM-B MEOs C225 and C226 orbits reaches 18 cm. This figure is approximately four to nine times those for other BeiDou-3 MEOs. This contradicts the fact that the orbit quality of C225 and C226 is comparable to other satellites. By analyzing the correlation between SLR residuals and de-trend clock residuals, detector-specific bias performance, and the distribution characteristics of SLR residuals relative to satellite azimuth and nadir angles, we diagnose that abnormal SLR validation results for C225 and C226 originate from a large deviation in the official horizontal offsets for the laser retroreflector arrays (LRAs) in the satellite reference frame. LRA horizontal offsets for C225 and C226 are estimated based on SLR residuals. With our adjusted LRA offset estimates, the SLR residual metrics for C225 and C226 orbits (across various IGS/MGEX ACs) are comparable to the results obtained for other BeiDou-3 MEOs. Additionally, our adjustments enable the identification of their orbit modeling errors across different IGS/MGEX ACs according to the pattern of SLR residual variation. From the study, spacecraft manufacturers should be encouraged to conduct a comprehensive review of ground calibrations for BeiDou LRA offsets. This is crucial for optimizing BeiDou orbit model and enhancing its applications in high-precision geosciences.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The yaw mode history of BDS-2 IGSO/MEOs since 2016 is inferred from reverse kinematic precise point positioning. Experimental results show that C06 (IGSO-1) and C14 (MEO-6) satellites have abandoned ...the orbit-normal (ON) attitude mode in favor of continuous yaw-steering (CYS) mode since March and September 2017, respectively. BDS C13 (IGSO-6), launched in March 2016, and C16 (IGSO-7) always adopt the CYS mode during eclipse seasons. The majority of BDS-2 IGSO/MEOs still experience attitude switches between nominal and ON mode. Most of the attitude switches from nominal to ON mode take place when the sun elevation angle above the orbital plane (
β
angle) decreases below 4°
(
β
<
4
∘
)
. A few switches also occur for
β
slightly above 4°. However, most of the attitude switches from ON to nominal mode are undertaken when
β
increases to above 4°, but a few switches with
β
just below 4° happen. The exact switch condition between the two attitude modes is presented in this study. For BDS-2 IGSO/MEOs using the CYS mode, the yaw-attitude model previously established by the Wuhan University (indicated by WHU model) can basically reproduce their yaw maneuvers. However, reverse midnight-turn maneuvers occasionally occur for C13 and C14 for
β
angles falling into the range
(
0
∘
,
0
.
14
∘
)
. This discrepancy in the form of a reversal in the yaw direction during the noon-turn maneuvers is first observed for C13 and C14 when the
β
angle is in the range of
(
-
0
.
14
∘
,
0
∘
)
. The mismodeling of the satellites attitudes during reverse yaw maneuvers significantly degrades the performance of BDS precise orbit determination (POD). The phase observation residuals extracted from BDS POD reach 40 cm, which thereby leads to the misidentification of a substantial number of observations around orbital midnight and noon points as outliers when the WHU model is applied in our experiments. The WHU model is modified to reproduce the reverse yaw maneuvers of satellites in the post-processing BDS POD. The derived phase residuals decrease to normal levels, and the clock solutions become smoother relative to solutions employing the WHU model.
Full text
Available for:
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 presence of non-negligible atmospheric delays and multipath errors makes it difficult for the long-range baselines to provide high-accuracy real-time kinematic (RTK) deformation monitoring ...services, as is the case for short baseline. Despite considerable efforts to model the effects of tropospheric errors, multipath errors remain a challenging issue in high-accuracy GNSS positioning applications. We describe a strategy for mitigating the multipath errors in long-range baselines, enabling precise RTK positioning results. First, the double-differenced ionospheric-free residuals are converted to un-differenced (UD) residuals for each satellite of the associated stations. The troposphere and multipath are the main error sources in these UD residuals. Taking advantage of the different features of UD tropospheric and multipath errors when displayed as a function of the scale factors provided by the wet mapping functions, the residual zenith tropospheric delays of each station are therefore constructed and used to resolve the practical tropospheric errors of each slant signal. The multipath errors are extracted by subtracting the computed tropospheric errors from the converted UD ionospheric-free residuals. After correcting the tropospheric and multipath errors, high-accuracy RTK positioning results can be obtained from long-range baselines. Compared with traditional methods, the proposed approach gives a 43.2% improvement in the average 3D root mean square error. Moreover, improvements of 22.2%, 52.4%, and 47.3% are achieved in the east, north, and up components for a 127 km baseline, giving a final epoch-wise positioning accuracy of 6.2 mm, 4.3 mm, and 11.8 mm, respectively. Experimental results show that the proposed strategy is an efficient and promising method in high-accuracy deformation monitoring applications for long-range baselines.
Full text
Available for:
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
In order to obtain high-precision positioning, precise point positioning (PPP) user side should keep the the consistent satellite attitude model with analysis centers. Based on the satellite attitude ...quaternions products provided by the Wuhan university analysis centers (WUM), we introduce the yaw angle computation method that uses satellite attitude quaternions. When the BDS-2/BDS-3 satellite is at a low sun elevation angle, the satellite attitude model strategy of WUM is analyzed. By using the open-source positioning software GAMP, the BDS-2/BDS-3 PPP solutions are also investigated with different satellite attitude strategies. During the deep eclipse season, the results demonstrate that the differences between nominal and quaternion yaw angles can reach 360°, which can cause the decimeter-level biases in the phase wind-up and antenna phase center offset correction. In this period, compared with the nominal attitude, the positioning accuracy of PPP solutions with satellite attitude quaternions can be improv
