Search

The BeiDou Navigation Satellite System (BDS) broadcasts the BDS Klobuchar model (BDSK) for ionospheric delay correction in both BDS-2 regional service phase and BDS-3 global service phase. Unlike the GPS Klobuchar model, the BDSK model adopts a simple "symmetrical strategy" due to the limited ionospheric input data within China, which results in inaccurate total electron content (TEC) estimation in the southern hemisphere. Besides, the "high latitude anomaly" occurs in the BDSK model due to the lack of latitude limitation strategy, which deteriorates the accuracy of the BDSK model in the southern hemisphere further. To solve this problem, we propose a revised BDS Klobuchar model (RBDK), in which the "non-symmetrical strategy" is adopted in the southern hemisphere and an amplitude constraint is introduced at high latitudes. For comparison, the fitted BDS Klobuchar model (BDFK) that is estimated using the same ionospheric input data and constraint algorithm for the RBDK model but with the "symmetrical strategy" is also included. First, we conduct a comparative analysis of the time series of the eight parameters for the BDSK, BDFK and RBDK models in 2021. The parameters of the BDFK and RBDK models are more stable, and there will be no abnormal jumping phenomenon that occurs in the BDSK model. Then, the performance of the broadcast BDSK model, the fitted BDFK model and the proposed RBDK model during the whole year of 2021 are evaluated by comparing them with the high-precision global ionospheric map (GIM) of the International GNSS Service (IGS). In the southern hemisphere, the root mean square (RMS) values of the BDSK and BDFK are 6.5 and 5.8 TEC unit (TECU), respectively, while that of the RBDK is 4.6 TECU, showing improvements of 29% and 21%, respectively. At high latitudes in the northern hemisphere, the RMS value of the BDSK is 7.6 TECU, while they are only 3.7 TECU for the RBDK and BDFK when the amplitude constraint is introduced. Final, we select 16 IGS stations to validate the performance of the BDSK, BDFK and RBDK models in the standard point positioning (SPP) domain in 2021. The average SPP accuracy of the BDSK is 8.88 m at 6 high-latitude stations, while they are 5.48 m for the RBDK and BDFK, showing significant improvement of 38%. Excluding the high-latitude stations, the SPP accuracy of the RBDK outperforms the BDFK and BDSK by 14% and 18%, respectively, at stations in the southern hemisphere. As expected, the proposed RBDK model shows significantly better performance in the southern hemisphere and at high latitudes in contrast to the broadcast BDSK model. [ABSTRACT FROM AUTHOR]

Precise point positioning (PPP) can measure ground motions with a centimetre-level accuracy using only one receiver. It has been widely used in earthquake monitoring and earthquake early warning (EEW) systems. However, traditional PPP highly depends on well-established and robust internet infrastructure for data communication. Along with the broadcast ephemeris, the orbit and clock corrections transmitted by the B2b signals of BeiDou Navigation Satellite System (BDS) can be used to recover the precise products of GPS and BDS. Since the B2b products, namely the satellite state parameter messages, are accessible even without internet infrastructure, PPP with B2b signals is more suitable for real-time applications. This study witnesses the application of PPP with B2b products in seismic monitoring for the first time. The shake table experiments demonstrate that PPP with B2b can reach a millimetre-level accuracy in horizontal in earthquake monitoring for GPS-only, BDS-only and GPS/BDS combination. The application to the 2021 M w 7.4 Maduo earthquake shows that the accuracies of seismic displacements derived from GPS-only PPP with B2b products are 1.7, 2.4 and 1.7 cm in east, north and vertical components, compared with those from GPS-only PPP with final precise products. We therefore conclude that PPP with B2b products has a promising prospect in seismogeodesy and related applications such as EEW and rapid hazard response. [ABSTRACT FROM AUTHOR]

We present a new method using Global Navigation Satellite System‐derived peak ground velocities to rapidly determine rupture characteristics for large earthquakes (Mw > 6). A three‐step strategy is adopted to sequentially estimate the fault rupture length, direction, and pattern (unilateral or bilateral). It does not require any a priori constraint on the fault plane, and can avoid drift and clipping problems in seismic data based inversion methods. Through retrospective analysis of six recent large earthquakes, the line‐source rupture characteristics can be determined within 30 s. Comparison with the United States Geological Survey released products demonstrates that the line‐source parameters can be estimated with considerable accuracy. We also analyze the contribution of the earthquake rupture characteristics to the prediction of ground shaking intensity. It is shown that the method has the potential to improve ground shaking predictions with applications in disaster assessment and emergency response. Plain Language Summary: Rapid generation of ground shaking maps after an earthquake is of great importance to identify serious damage regions. Timely information of large earthquake rupture characteristics (e.g., rupture length, direction, and pattern) helps improve the estimates of ground shaking maps. The traditional methods to estimate the rupture characteristics can be hindered by the overdependence on seismic data that may be unreliable for displacement estimation in the near‐field of large earthquakes. We propose a new method of rupture characteristics estimation using geodetic velocity waveforms from Global Navigation Satellite System recordings. Our method does not require any pre‐defined fault geometric information and can avoid drift and clipping problems suffered in traditional methods. Through retrospective analysis of six recent large events, we show that the method can efficiently estimate line‐source rupture characteristics within 30 s with considerable accuracy. The estimates of the rupture characteristics can improve ground shaking predictions and are expected to be applied in disaster assessment and emergency response. Key Points: We propose a new method for the rapid inversion of large earthquake rupture characteristics using high‐rate Global Navigation Satellite System dataThe fault rupture length, direction, and pattern (unilateral or bilateral) can be rapidly determined with considerable accuracyThe estimates of the rupture characteristics are expected to refine ground shaking predictions for large earthquakes (Mw > 6) [ABSTRACT FROM AUTHOR]

High-rate global navigation satellite system (GNSS) has emerged as an effective method to recover seismic waveforms without saturation and drifts, but it has the limitation of relatively lower sampling rate and higher noise level compared to seismic instruments. In this study, we present a new seismogeodetic method by integrating GNSS and accelerometer data to obtain optimal real-time seismic waveforms. Unlike traditional integration methods based on GNSS techniques of relative positioning or precise point positioning, the new method uses a GNSS time difference technique and inherits its unique advantage in real-time and high-accuracy velocity solutions. Furthermore, by incorporating the tightly coupled structure, it can overcome the cascading problem and provide more accurate and robust waveforms compared to its loosely coupled counterpart. The performance of this method is first compared with the traditional loosely coupled approach in challenging environments through a set of shake table experiments. With three GNSS satellites, this approach method can improve the accuracy of velocities and displacements by 42 and 87 per cent, respectively. With four or more GNSS satellites, the average improvements of the method reach 25 and 41 per cent for the velocities and displacements, respectively. We then validate the full performances of the method through simulated shake table experiments and collocated GNSS and accelerometer data during the 2016 M w 6.6 central Italy earthquake. The simulated and real-event analyses demonstrate that the new integration method can take full advantage of the complementary characteristics of GNSS and accelerometer sensors. By providing more accurate and broad-band velocity and displacement waveforms in a real-time or near-real-time manner, this method is quite promising in earthquake early warning and rapid source inversion. [ABSTRACT FROM AUTHOR]

The continuously developing Global Navigation Satellite Systems (GNSS), in particular with the latest operational BDS and Galileo, provide good opportunities to enhance the performance of precise positioning. This study evaluates the performance of high-rate precise point positioning (PPP) applied for seismogeodesy with very recent BDS and Galileo. The static experiments with 20-Hz GNSS data show that Galileo and BDS-3/BDS-2 achieve comparable performances, with average 3D RMS values of 0.6–1.3 cm and 0.8–1.2 cm, respectively. In the dynamic experiments, we use a single-axis earthquake simulator of Quanser Shake Table II to simulate seismic waveforms of real earthquakes and collect 20-Hz GNSS data to evaluate the PPP performance. Taking the displacements recorded by the embedded encoder of the shake table as the truth, the accuracies of PPP displacements during the seismic events are 4–8 mm for GPS, 6–9 mm for BDS-2, and 3–6 mm for Galileo and BDS-3/BDS-2. By combining BDS-3 with BDS-2, the positioning accuracy of BDS is improved by 50% with respect to BDS-2 only. Galileo and BDS-3/BDS-2 perform slightly better than GPS, which is likely because the two latest operational systems use the more precise passive hydrogen maser clocks and have lower signal-in-space range error. The multi-GNSS solutions with GPS + Galileo + BDS-3/BDS-2 further improve the accuracy reaching 2–5 mm. We also identify a scale factor in the high-rate PPP displacements, which is probably induced by the dynamic stress error and related to the oscillating frequency. The scale factor reaches the maximum of 1.71 at an oscillating frequency around 2.5 Hz and then descends as the frequency increases. The improved performance of high-rate PPP augmented by the recent BDS-3 and Galileo is helpful to improve the practical level of high-rate GNSS in seismogeodesy and expand its applications to many other high-rate and high-accuracy applications. [ABSTRACT FROM AUTHOR]

Global Positioning System technique has been widely used to estimate ocean tide loading displacements, but classical harmonic analysis with satellite modulation typically disregards the effects of hundreds of minor tides within the same tidal species of major tides. We present an improved harmonic analysis of eight major tidal constituents (M2, S2, N2, K2, K1, O1, P1 and Q1) that are adjusted by more adjacent minor tides in semidiurnal and diurnal species than the usual satellite modulation approach, through the tidal admittance interpolation. Our results show that this approach allows for a more reliable determination of GPS-observed N2, Q1, P1 and S2 constituents in the northwest European shelf than the classical method, as demonstrated by a comparison with FES2014b and TPXO9-Atlas ocean tide model predictions. The advantages of our method are more pronounced in the harmonic analysis of GPS time series of short duration (1–2 years) than long duration. These improvements mainly depend on some inferred minor tides with larger equilibrium amplitudes, which provide effective admittance constraints to major tidal estimation. Among the major tidal estimates, the most significant improvement is seen for the N2 constituent (with the maximum improvement of 9.9%, 9.0% and 9.7% for the up, east and north components in terms of agreement with FES2014b model predictions), particularly along the Wadden Sea coast where significant satellite modulation deviations occur. [ABSTRACT FROM AUTHOR]

As an attractive technique for measuring water vapor, the Global Navigation Satellite System (GNSS) faces additional challenges in dynamic applications such as in the open sea. We present a new method of retrieving precipitable water vapor (PWV) based on GNSS multi‐antenna precise point positioning (PPP), which uses GNSS data from multiple antennas and incorporates the constraints of known baseline vector and common tropospheric delay. The 4‐day shipborne dynamic experiment along the China coast demonstrates that the baseline vector constraint shortens the convergence time of positioning and atmospheric parameters, and also slightly improves their accuracies. The common tropospheric delay constraint helps to provide compromised, more robust, and sometimes more accurate PWV estimates. An evaluation with radiosonde‐derived PWVs shows that the combination of the two constraints achieves the best accuracy reaching 4.2 mm. This method helps to expand GNSS meteorology to the vast ocean and benefits satellite altimetry and weather forecasting. Plain Language Summary: Water vapor plays an important role in atmospheric processes ranging from global climate change to mesoscale and micro‐scale weather systems. The Global Navigation Satellite System (GNSS) is an attractive technique to measure water vapor, which has been extensively investigated for ground‐based static stations. In dynamic applications such as in the open sea, it is faced with additional challenges which may potentially degrade the performance. This study presents a new method for retrieving precipitable water vapor (PWV) based on GNSS multi‐antenna precise point positioning (PPP). It uses GNSS data from multiple antennas closely spaced and mounted on the same platform, and incorporates additional constraints of known baseline vector and common tropospheric delay. We have conducted a 4‐day shipborne dynamic experiment along the China coast and demonstrated that this method can shorten the convergence time and provide more robust and sometimes more accurate PWVs compared to conventional PPP. An accuracy level of 4.2 mm is achieved with this method for the ocean‐based dynamic experiment. This study helps to expand GNSS meteorology to challenging environments such as in the open sea, which will benefit weather forecasting and nowcasting. Key Points: A new method of retrieving precipitable water vapor (PWV) is presented based on Global Navigation Satellite System (GNSS) multi‐antenna precise point positioning (PPP)This method can shorten the convergence time and provide more robust and more accurate GNSS‐based PWVThe improved performance is helpful to expand GNSS meteorology to the vast ocean and benefits satellite altimetry and weather forecasting [ABSTRACT FROM AUTHOR]