We present a new method of integrating Global Positioning System (GPS) and accelerometer data for high‐rate seismogeodesy. This method is based on the GPS variometric approach which can obtain seismic waves in real time using only the readily available broadcast products and a single receiver. Collocated 1‐Hz GPS and 200‐Hz accelerometer data from the 2016 M_W 7.8 Kaikōura earthquake were analyzed to verify the effectiveness of this method. Results reveal that this method can provide broadband and more accurate velocities and displacements qualified to detect P wave arrivals. Moreover, this method can effectively avoid the aliasing problem present in the 1‐Hz GPS waveforms. We therefore conclude that this new method can be a powerful tool to capture seismic waves in real time, which is crucial for the purpose of tsunami early warning and earthquake rapid response.

The international GNSS monitoring and assessment system (iGMAS) tracking network has been established by China to track multi-GNSS satellites. A key feature of iGMAS stations is the capability to fully track new navigation signals from the recently deployed BDS-3 satellites. In addition to the B1I and B3I signals inherited from BDS-2 satellites, the BDS-3 satellites are capable of transmitting new open service signals, including B1C at 1575.42 MHz, B2a at 1176.45 MHz, and B2b at 1207.14 MHz. In this contribution, we present a comprehensive analysis and characterization of GNSS signals tracked by different receivers and antennas equipped in the iGMAS network, especially as they relate to BDS-3 signals. Signal characteristics are analyzed in terms of the carrier-to-noise density ratio for the different signals as measured by the receiver, as well as pseudo-range noise and multipath. Special attention is given to discussion of the satellite-induced code bias, which has been identified to exist in the code observations of BDS-2, and the inter-frequency clock bias (IFCB), which has been observed in the triple-frequency carrier phase combinations of GPS Block IIF and BDS-2 satellites. The results indicate that the satellite-induced code bias is negligible for all signals of BDS-3 satellites, while small IFCB variations with peak amplitudes of about 1 cm can be recognized in BDS-3 triple-carrier combinations.

Differential code biases (DCBs) are important parameters in GNSS (Global Navigation Satellite System) applications such as positioning as well as ionosphere remote sensing. In comparison to the conventional approach, which utilizes ground-based observations and parameterizes global ionosphere maps together with DCBs, a method is presented for GPS and BeiDou system (BDS) satellite DCB estimation using onboard observations from the Chinese Fengyun-3C (FY3C) satellite. One month worth of GPS and BDS data during March 2015 was exploited and the GPS C1C-C2W and BDS C2I-C7I DCBs were explored. To improve DCB estimation precision, the dual frequency carrier phase measurements leveled by code measurements were used to form basic observation equation. Code multipath errors of the FY3C onboard GPS/BDS observations were assessed and modeled as grid maps, and their impact on DCB estimation was analyzed. By correcting code multipath errors, the stability of DCB estimates was improved by 5.0%, 3.1%, 16.2% and 13.6% for GPS, and BDS geosynchronous orbit satellites (GEOs), inclined geosynchronous satellite orbit satellites (IGSOs) and medium Earth orbit satellites (MEOs), respectively. The monthly stability of FY3C-based DCBs was at the order of 0.1 ns for GPS satellites, 0.2 ns for BDS GEOs and 0.1 ns for BDS IGSOs and MEOs. By comparison to the ground-based DCB products issued by other institutions, FY3C-based DCBs showed stability degradation for BDS C02 and C05 satellites, while, for other satellites, the stability reached a similar or even superior level. The estimated FY3C receiver DCB stability was at the order of 0.2 ns for both GPS and BDS. In addition to the DCB estimates, the obtained vertical total electron content above the FY3C satellite orbit was also investigated and its realism was examined in physical and numerical aspects.

The accurate assessment of railway irregularities plays a pivotal role in ensuring both operational safety and passenger comfort, especially in the context of high-speed railways. Traditional static methods for monitoring these irregularities, such as absolute measurement trolley systems relying on total stations, have proven to be inefficient. On the other hand, relative measurement systems like the global navigation satellite system/inertial navigation system (GNSS/INS) integrated concept offer high operational efficiency but come with substantial costs associated with navigation-grade inertial measurement unit (IMU) systems. In this research endeavor, we introduce a novel multisensor fusion system centered around a relative inspection trolley. This innovative approach serves to significantly reduce equipment expenditures while simultaneously elevating the accuracy of irregularity detection. The core components of this system comprise real-time kinematic (RTK) GNSS, a cost-effective micro-electric mechanical system (MEMS) IMU, an odometer, and two laser modules. The integration of various advanced techniques, including zero velocity update (ZUPT), Ranch-Tung-Striebel smoother (RTS), nonholonomic constraint (NHC), odometer calibration (OC), and prior knowledge (PK), collectively enhances the efficiency and precision of railway irregularity measurements. The results obtained from extensive testing on railway irregularities demonstrate the remarkable capabilities of the proposed system. It exhibits a measurement precision of approximately 0.2, 1.0, 0.7, 0.5, and 0.5 mm for rail gauge, cross level, twist, vertical irregularities, and lateral irregularities, respectively. Consequently, our suggested technique stands as a compelling choice for the precise quantification of railway irregularities, offering a compelling solution for the railway industry.