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GPS Solutions
Journal Prestige (SJR): 1.674
Citation Impact (citeScore): 5
Number of Followers: 28  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1521-1886 - ISSN (Online) 1080-5370
Published by Springer-Verlag Homepage  [2467 journals]
  • Adaptive Kalman filter based on integer ambiguity validation in moving
           base RTK

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      Abstract: Abstract In high-precision dynamic positioning, it is necessary to ensure the positioning accuracy and reliability of the navigation system, especially for safety–critical applications, such as intelligent vehicle navigation. In the face of a complex observation environment, when the global navigation satellite system (GNSS) uses carrier phase observations for high-precision relative positioning, ambiguity resolution will be affected, and it is difficult to estimate all ambiguities. In addition, when the GNSS signal quality and measurement noise level are difficult to predict in an environment with many occlusions, the received satellite observations are prone to very large errors, resulting in apparent deviations in the positioning solution. However, traditional positioning algorithms assume that the measurement noise is constant, which is unrealistic. This will cause incorrect ambiguity resolution, lead to meter-level positioning errors, reduce the reliability of the system, and increase the integrity risk of the system. We proposed an innovative adaptive Kalman filter based on integer ambiguity validation (IAVAKF) to improve the efficiency of ambiguity resolution (AR) and positioning accuracy. The partial ambiguity resolution (PAR) method is applied to solve the integer ambiguities. Then, the accuracy of the fixed ambiguity is verified by the ambiguity success rate. Taking the ambiguity success rate as a dynamic adjustment factor, the measurement noise matrix and variance–covariance matrix of the state estimation is adaptively adjusted at each time interval in the Kalman filter to provide a smoothing effect for filtering. The optimal Kalman filter gain matrix is obtained to improve positioning accuracy and reliability. As a result, the static and dynamic vehicle experiments show that the positioning accuracy of the proposed IAVAKF is improved by 26% compared with the KF. Through the IAVAKF, a more realistic PL can be obtained and applied to evaluate the integrity of the navigation system in the position domain. It can reduce the false alarm rate by 2.45% and 1.85% in the horizontal and vertical directions, respectively.
      PubDate: 2022-12-05
       
  • Initial performance assessment of the single-frequency (SF) service with
           the BeiDou satellite-based augmentation system (BDSBAS)

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      Abstract: Abstract The BeiDou satellite-based augmentation system (BDSBAS) is expected to provide single-frequency (SF) service through B1C signals for users in Chinese mainland and the surrounding areas, in accordance with the standards of the International Civil Aviation Organization (ICAO). The SF service of the BDSBAS is designed to augment both GPS and GLONASS with the performances meeting the requirements of approach with vertical guidance (APV-I), and initial SF service has been provided for test since July 2020. To comprehensively assess the performance of the SF service before its official application to civil aviation users, experiments were conducted with data collected at more than 30 stations all over the BDSBAS service area during the year of operation to June 30, 2021. With the BDSBAS corrections being applied, the average 95th percentiles of horizontal and vertical positioning errors are improved by 45.7% and 41.9% to 1.45 m and 2.77 m, respectively. The horizontal and vertical availabilities of the BDSBAS are 99.98% and 99.89%, respectively, and no risky event of integrity occurs throughout the year. The BDSBAS has generally achieved stable operation and has the capacity to routinely provide single-frequency positioning service as designed. According to the standards of the ICAO, the SF service with the BDSBAS is able to satisfy the positioning accuracy requirement of APV-I operation and has the potential to meet the requirements on availability and integrity.
      PubDate: 2022-12-05
       
  • Snow depth estimation from GNSS SNR data using variational mode
           decomposition

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      Abstract: Abstract In recent years, Global Navigation Satellite System-Interferometric Reflectometry (GNSS-IR), a new remote sensing technique, has been widely used to monitor surface signature parameters. In the classical GNSS-IR technology, poor signal separation will seriously affect the accuracy of the inversion results. In order to better separate the signal-to-noise ratio trend item, the variational mode decomposition (VMD) algorithm is introduced. We use the GNSS data of P351 station in 2013–2014 and AB33 station in 2017 in the Earthscope Plate Boundary Observatory network to carry out snow depth inversion experiments. The measured snow depths provided by the Snowpack Telemetry network were used for the validation of the inversion accuracy. The feasibility and superiority of the VMD algorithm in GNSS-IR snow depth inversion experiments were verified by analyzing the experimental results. The root-mean-square error (RMSE) and correlation coefficient of the inversion results of P351 station in 2013–2014 were 13.41 cm and 0.99, respectively, which improved the inversion accuracy by about 54%. Moreover, the number of inversion points during the experimental period increased from 19,997 to about 26,958, which is an increase of about 35%. Similarly, the RMSE and correlation coefficient of the inversion results of AB33 station in 2017 reached 8.55 cm and 0.97. Compared with the traditional algorithm, the accuracy and the number of inversion points increased by about 15% and 22%, respectively.
      PubDate: 2022-12-04
       
  • The GUARDIAN system-a GNSS upper atmospheric real-time disaster
           information and alert network

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      Abstract: Abstract We introduce GUARDIAN, a near-real-time (NRT) ionospheric monitoring software for natural hazards warning. GUARDIAN’s ultimate goal is to use NRT total electronic content (TEC) time series to (1) allow users to explore ionospheric TEC perturbations due to natural and anthropogenic events on earth, (2) automatically detect those perturbations, and (3) characterize potential natural hazards. The main goal of GUARDIAN is to provide an augmentation to existing natural hazards early warning systems (EWS). This contribution focuses mainly on objective (1): collecting GNSS measurements in NRT, computing TEC time series, and displaying them on a public website (https://guardian.jpl.nasa.gov). We validate the time series obtained in NRT using well-established post-processing methods. Furthermore, we present an inverse modeling proof of concept to obtain tsunami wave parameters from TEC time series, contributing significantly to objective (3). Note that objectives (2) and (3) are only introduced here as parts of the general architecture, and are not currently operational. In its current implementation, the GUARDIAN system uses more than 70 GNSS ground stations distributed around the Pacific Ring of Fire, and monitoring four GNSS constellations (GPS, Galileo, BDS, and GLONASS). As of today, and to the best of our knowledge, GUARDIAN is the only software available and capable of providing multi-GNSS NRT TEC time series over the Pacific region to the general public and scientific community.
      PubDate: 2022-12-03
       
  • Spatial interpolation of surface point velocity using an adaptive
           neuro-fuzzy inference system model: a comparative study

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      Abstract: Abstract Surface displacement measurements of the earth’s crust using GNSS observations are a discrete form and occur at the location of stations. Therefore, it is not possible to study crustal deformation as a continuous field. To overcome this problem, we propose the idea of using an adaptive neuro-fuzzy inference system (ANFIS) model. In the new method, the geodetic coordinates of GPS stations are input vectors, and the components of the displacement field in two-dimensions (Ve, Vn) are used as an output. The new method is analyzed using the observations of 25 GPS stations located in the northwest of Iran. Due to ample GPS stations and a tectonically active area, this region has been selected for study. The results of the new model are compared with the GPS-observed results, and with results produced by three alternative interpolation processes, namely artificial neural network (ANN), Ordinary Kriging (OK) and polynomial velocity field. The root-mean-square error (RMSE), correlation coefficient and relative error are calculated for all four interpolation processes. In the testing step, the averaged RMSE of the ANN, ANFIS, OK, and polynomial models is 2.0, 1.6, 2.7 and 3.2 mm year. The estimated velocity field by the ANFIS has been converted to a strain field and compared to the strain obtained from GPS measurements. Comparing the modeled strains with the ANFIS and GPS output for two control stations shows a correlation coefficient of 0.94 between the new model and GPS. The results reveal the capability and efficiency of ANFIS in comparison with ANN, OK and polynomial models.
      PubDate: 2022-12-02
       
  • NLOS signal detection and correction for smartphone using convolutional
           neural network and variational mode decomposition in urban environment

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      Abstract: Abstract With the rapid development of mobile communications, location-based service for smartphones has received extensive attention, becoming an indispensable part of smart cities. However, the positioning effect of smartphones in urban environments is not ideal, and the non-line-of-sight (NLOS) signal is one of the main limiting factors. To weaken NLOS signal errors, we present a method to detect and correct NLOS signals. An NLOS signal detection model based on a convolutional neural network is constructed using the original observations of smartphones. In an experimental environment, the detection accuracy of the model reaches more than 95%. The detected NLOS signals are decomposed using the variational mode decomposition method to eliminate the NLOS part and improve the data quality. To evaluate the effect of the proposed method, we conduct static and dynamic experiments in an urban environment. In the static experiment, the positioning accuracy of the processed data is improved by an average of 15% compared with the unprocessed data, and the stability of the plane results is also significantly enhanced. In the dynamic test, the dataset processed using the proposed method achieved a positioning accuracy of 3 m in an environment with severe signal occlusion, and the accuracy is improved by more than 20%. Although the accuracy in heavily occluded areas is still far from that in an open environment while only relying on the global navigation satellite system signal of smartphones, this method can still provide new ideas for smart city research and construction.
      PubDate: 2022-12-02
       
  • Improving undifferenced precise satellite clock estimation with BDS-3
           

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      Abstract: Abstract Estimates of satellite clock offsets typically employ dual-frequency undifferenced (UD) ionospheric-free (IF) observations from global network. The third-generation BeiDou Navigation Satellite System (BDS-3) can transmit B1I (1561.098 MHz), B3I (1268.52 MHz), B1C (1575.42 MHz), B2a (1176.45 MHz), B2b (1207.14 MHz) and B2ab (1191.795 MHz) signals. To make full use of the advantage of BDS-3 multi-frequency signals and improve BDS-3 service performance, we present some new quad-frequency satellite clock estimation techniques using B1I/B3I/B1C/B2a signals, which are QFIF0 model combining B1I/B3I and B1C/B2a IF observables, QFIF1 model combining the B1I/B3I, B3I/B1C and B1I/B2a IF observables, QFIF2 model combining B1I/B3I and B1I/B3I/B1C/B2a IF observables, and quad-frequency uncombined QFUC model, respectively. These new techniques only improve the performance of satellite clock estimation by fully utilizing the BDS-3 multi-frequency observations on the premise of ensuring the dual-frequency IF datum but also obtain the corresponding inter-frequency clock bias (IFCB) simultaneously. The quad-frequency satellite clock offsets are evaluated in terms of the clock offset precision, the modified Allan deviation (MDEV) and precise point positioning (PPP) performances. The new methods can improve the performances of the estimated clock offsets compared with the traditional dual-frequency IF model. The precision for the estimated clock offsets using quad-frequency satellite clock estimation models can be improved by 13–26% in terms of standard deviation (STD). The improvement of frequency stability ranges from 0 to 24%, especially for the short-term stability, which can reach 12% and 24% for B1I/B3I and B1C/B2a clock offsets, respectively. Similarly, the corresponding PPP performance has also been better improved with respect to those of using traditional dual-frequency IF clock offsets. Thus, the proposed quad-frequency satellite clock estimation techniques can be well applied into precise satellite clock estimation.
      PubDate: 2022-11-29
       
  • Global single-epoch narrow-lane ambiguity resolution with
           multi-constellation and multi-frequency precise point positioning

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      Abstract: Abstract Automatic driving has led to a great demand for global instantaneous high-precision precise point positioning (PPP). To achieve global instantaneous high-precision PPP, such as centimeter-level accuracy, global single-epoch narrow-lane (NL) ambiguity resolution (AR) is needed, which is quite difficult due to the limited accuracy of global atmospheric corrections. Multi-constellation and multi-frequency PPP wide-lane (WL) AR (PPP-WAR) provides a new approach to global single-epoch NL AR without atmosphere corrections because the instant NL ambiguity accuracies will be improved by fixing many WL ambiguities instantaneously. In this article, the uncombined PPP cascading WL/NL AR method (PPP-CAR) was extended to GPS, Galileo, BDS-2, and BDS-3 all-frequency signals to investigate global single-epoch NL AR with global public stations. The test results indicated that the instant positioning accuracies improved substantially with increasing frequencies for the single-epoch multi-frequency PPP-CARs, attributed to the contribution of the additional frequency observations. However, the same fixing rates of the NL ambiguities of 99.8% in all epochs were achieved for the single-epoch multi-frequency PPP-CARs, demonstrating that more reliable single-epoch NL ARs were reached with increasing frequencies. Only decimeter-level instant positioning accuracies were achieved for the dual-frequency, triple-frequency, and quad-frequency PPP-CARs. A centimeter-level global horizontal instant positioning accuracy of 0.07 and 0.08 m in the east and north components, respectively, was achieved by the five-frequency PPP-CAR for the first time. These results are very encouraging because better positioning is expected for global autonomous driving vehicles by integrating the multi-constellation all-frequency signals with other sensors, such as an inertial sensor.
      PubDate: 2022-11-29
       
  • An adaptive three-stage information filter of simultaneous state and
           unknown disturbance estimation in linear time-varying systems

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      Abstract: Abstract An adaptive three-stage information filter is proposed to estimate unknown disturbances in discrete linear time-varying systems. By modeling unknown dynamic faults and observation abnormalities as parameter changes, the proposed filter is designed as three detachable filters, including the main information filter and two compensation filters. A rule for detecting the unknown dynamic and observation disturbances is presented based on a generalized likelihood ratio test. Under the classical uniform complete observability–controllability conditions and a persistent excitation condition, the exponential stability of the adaptive three-stage information filter is rigorously analyzed. The numerical examples are presented to illustrate the performance of the proposed algorithm. The results show that the proposed filter is a better trade-off between algorithm simplicity and efficiency; after the dynamic and observation disturbances change, the disturbance compensation converges after a transient.
      PubDate: 2022-11-28
       
  • Optimization design of two-layer Walker constellation for LEO navigation
           augmentation using a dynamic multi-objective differential evolutionary
           algorithm based on elite guidance

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      Abstract: Abstract In recent years, low earth orbit navigation augmentation (LEO-NA) has attracted increasing attention and is expected to become a new addition to global navigation satellite systems (GNSSs). When solving complex constellation design problems, traditional optimization algorithms often fail to achieve satisfactory results and are sensitive to parameter settings. We propose a dynamic multi-objective differential evolutionary algorithm based on elite guidance (DMODE-EG). It can select the evolutionary strategy based on the evolutionary state reflected by elite individuals and dynamically modify evolution parameters. Moreover, to achieve more uniform global coverage, we construct a two-layer Walker constellation model for LEO-NA. Then, we use the DMODE-EG algorithm to solve the corresponding multi-objective optimization problem and obtain the optimal constellation parameters. With the augmentation of this LEO-NA constellation to the BeiDou-3 system, the average position dilution of precision (PDOP) values drop to 1.2–2.0 from 1.5–5.5, and the number of visible satellites increases from 8–10 to 13–18. By contrast, some realistic LEO constellations and constellations designed by other algorithms bring weaker improvements and cannot address the problem of high PDOP values in some regions. In addition, simulation results on standard test sets verify the excellent convergence and stability of the DMODE-EG algorithm.
      PubDate: 2022-11-27
       
  • On the potential of undifferenced and uncombined GNSS time and frequency
           

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      Abstract: Abstract The use of global navigation satellite systems (GNSS) has been a competitive way to provide high-precision and low-cost time and frequency transfer results. However, the traditional GNSS method, the precise point positioning (PPP), is usually based on the ionosphere-free (IF) combination, which is not flexible when applying multi-frequency scenarios. In addition, PPP relies on precise satellite clock products with an accuracy of tens of picoseconds, limiting the time and frequency transfer performance. More importantly, achieving integer ambiguity resolution (IAR) is challenging, which makes high-precision phase observations underutilized. To achieve a better time transfer performance, we must consider all those factors from the GNSS end. In this contribution, a new GNSS time and frequency model at the undifferenced and uncombined (UDUC) level is first derived. In the UDUC model, the satellite clocks are estimated together with other parameters, and the integer ambiguities are resolved in the double-differenced (DD) form for their reliable estimation. Our numerical tests suggest three major findings. First, with integer ambiguities resolved, the UDUC model with satellite clocks fixed showed a 20% to 50% improvement compared with the UDUC PPP model. Second, with IAR and satellite clocks estimated, the proposed UDUC model shows a 10%–40% improvement over the model with satellite clocks fixed. Third, with integer ambiguities resolved and satellite clocks estimated, GPS, Galileo, and BDS-3 all have the potential to achieve frequency transfer in the low-mid \(10^{ - 17}\) range for averaging times within one day.
      PubDate: 2022-11-23
       
  • 5G Impacts analysis on the Beidou RDSS system in 2.5 GHz band

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      Abstract: Abstract Beidou and 5G systems are important national-level basic projects. Beidou’s Radio Determination Satellite Service (RDSS) provides a unique service compared with other Global Navigation Satellite System (GNSS). The working RDSS frequency is close to 5G, and the received power is far less than 5G. Thus, RDSS is vulnerable to interference from 5G and loses normal function. The basic theory is the core evaluation model of the Adjacent Channel Interference Ratio (ACIR). Three critical factors, the 5G system, the signal design, and the receiver of RDSS are extracted and considered under the rule of ACIR. We obtained the safe distance making the two systems coexist by the deterministic analysis method and used the method of Monte Carlo system simulation to analyze the effects on Carrier-to-Noise power spectral density ratio (CN0), positioning and communication of RDSS users due to 5G adjacent interference. Three different types of Radio Frequency (RF) front-ends are designed, and their performance in suppressing adjacent frequency interference is analyzed under actual signal conditions. Through this research, we summarize the exact scope of adjacent frequency impact from two aspects of 5G and RDSS systems. Suggestions on how to enhance the electromagnetic protection ability are made for RDSS receivers.
      PubDate: 2022-11-19
       
  • An efficient strategy for multi-GNSS real-time clock estimation based on
           the undifferenced method

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      Abstract: Abstract Precise satellite clock product is an indispensable prerequisite for the real-time precise positioning service. To meet the requirement of numerous time-critical applications, real-time satellite clock corrections need to be broadcast to users with an update rate of 5 s or higher. With the rapid development of global navigation satellite systems (GNSS) over the past decades, abundant GNSS tracking stations and modern constellations have emerged, and the computation for multi-GNSS real-time clock estimation has become rather time-consuming. In this contribution, an efficient strategy is proposed to achieve high processing efficiency for multi-GNSS real-time clock estimation, wherein undifferenced method based on sequential least square is adopted. In the proposed strategy, parallel data processing and high-performance matrix operations are introduced to accelerate the processing of multi-GNSS clock estimation. The former is based on OpenMP (Open Multi-Processing), while the latter is achieved by the implementation of the Schur complement and the open-source library OpenBLAS. Multi-GNSS observations from 85 globally distributed tracking stations are employed for the generation of real-time precise clock products. The average elapsed time per epoch with the proposed strategy is 0.35, 0.68, and 2.30 s for GPS-only, dual-system, and quad-system solutions, respectively. Compared to the traditional serial strategy, the computation efficiency is significantly improved by 76.0%, 77.3%, and 77.7%, respectively. The accuracy of the estimated clocks is evaluated with respect to IGS final GPS clock products and GFZ final multi-GNSS clock products (GBM0MGXRAP), and multi-GNSS real-time precise point positioning (PPP) experiments are further carried out. All the results indicate that the proposed strategy is efficient, accurate, and can promise high-rate multi-GNSS real-time clock estimation.
      PubDate: 2022-11-18
       
  • An enhanced positioning algorithm module for low-cost GNSS/MEMS
           integration based on matching straight lane lines in HD maps

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      Abstract: Abstract Automated driving technology relies heavily on continuous, high-precision, and high-reliability positioning in complex urban situations. With the mass production of autonomous vehicles, the issue of keeping equipment as cheap as possible while maintaining precision is getting much attention. The low-cost global navigation satellite system (GNSS)/micro-electro-mechanical system (MEMS) integrated navigation system, as the mainstream solution, is often faced with MEMS dead-reckoning rapid divergence during GNSS outages. Meanwhile, the high-definition maps (HD maps), as the positioning resource which stores the absolute coordinate information, cover urban roads more and more perfectly. In this case, we propose a method to enhance low-cost GNSS/MEMS integrated positioning by using a monocular camera and straight lane lines in HD maps. The positioning results are corrected by projecting lanes from OpenDRIVE maps onto the image, matching them with the visually detected ones, and minimizing the reprojected linear coefficients residuals. The algorithm can be embedded into GNSS/MEMS integrated navigation system as a module without breaking the architecture and increasing the cost. The feasibility and influencing factors were analyzed in simulation and field experiments. The tests demonstrate that positions in the lateral and up directions can be corrected to within 10 cm under current HD maps accuracy. Moreover, it is not seriously limited by the initial pose error, the number of lanes, and the road flatness. The results indicate that the lane coefficients-based algorithm is a potential module for enhancing the low-cost GNSS/MEMS integrated positioning performance.
      PubDate: 2022-11-16
       
  • Influence of flooding on GPS carrier-to-noise ratio and water content
           variation analysis: a case study in Zhengzhou, China

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      Abstract: Abstract Based on the Global Positioning System interferometric reflectometry (GPS-IR), the influence of flood on GPS carrier-to-noise ratio (CNR) and water content variation is analyzed by using data sets collected during (day-of-year) DOY 197–206, 2021. The observation station ZHNZ is located in Zhengzhou, China, and is operated by the Crustal Movement Observation Network of China. The flood occurred on DOY 201, 2021, which was caused by heavy rain that lasted for three days. Experimental results showed that the CNR on L1 and L2 frequencies decreased during the flood, especially for elevations larger than 50 deg. In addition, affected by the surrounding of the observation station and the tracks of the satellites, the extent and duration of the impact of the flood on each satellite slightly differ. Before analyzing the water content variation by using CNR, the influence of the station environment, satellite trajectory, signal frequency, and satellite type is investigated. Moreover, real data sets were used to validate the importance of the independent calculation of the effective reflector height. The results showed that the effective reflector height performs independently of the satellite and slightly varies over time. The CNR was used to analyze the water content variation; experimental results demonstrated that the water content variation retrieved by CNR correlates consistently with the real observed rainfall overall. Although the correlation between the calculated volumetric water content and precipitation was only approximately 0.57, it was mainly induced by the influence of soil saturation caused by continuous and heavy rain.
      PubDate: 2022-11-09
       
  • A new global TEC empirical model based on fusing multi-source data

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      Abstract: Abstract The global TEC empirical model established with the TEC grid data of IGS as the background has poor prediction accuracy in marine areas, and its ability to describe some ionospheric anomalies is insufficient. In response to the above two problems, we use spherical harmonic (SH) to fuse multi-source TEC data as a modeling dataset and evaluate the accuracy of the fused products. When modeling, we consider three ionospheric anomalies, namely mid-latitude summer nighttime anomaly (MSNA), equatorial ionization anomaly (EIA), and “hysteresis effect,” and establish corresponding model components. We apply the nonlinear least-squares method to establish a global ionospheric TEC empirical model called the TEC model of multi-source fusion (TECM-MF) and verify the model. Results show that: (i) fusion products are valid and reliable modeling data for building global TEC model. (ii) The TECM-MF fits the Fusion TEC input data with a zero bias and a RMS of 3.9 TECU. The model can better show the diurnal, seasonal, and annual variations of the fusion dataset and the “hysteresis effect” of TEC. (iii) In the MSNA area, the prediction ability of the TECM-MF is better, the standard deviation is lower than that of NTCM-GL and Nequick2, close to 1 TECU, and the accuracy is consistent with IRI2016.
      PubDate: 2022-11-08
       
  • Investigating temporal and spatial patterns in the stochastic component of
           ZTD time series over Europe

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      Abstract: Abstract The EUREF Permanent GNSS Network (EPN) provides a unique atmospheric dataset over Europe in the form of Zenith Total Delay (ZTD) time series. These ZTD time series are estimated independently by different analysis centers, but a combined solution is also provided. Previous studies showed that changes in the processing strategy do not affect trends and seasonal amplitudes. However, its effect on the temporal and spatial variations of the stochastic component of ZTD time series has not yet been investigated. This study analyses the temporal and spatial correlations of the ZTD residuals obtained from four different datasets: one solution provided by ASI (Agenzia Spaziale Italiana Centro di Geodesia Spaziale, Italy), two solutions provided by GOP (Geodetic Observatory Pecny, Czech Republic), and one combined solution resulting from the EPN’s second reprocessing campaign. We find that the ZTD residuals obtained from the three individual solutions can be modeled using a first-order autoregressive stochastic process, which is less significant and must be completed by an additional white noise process in the combined solution. Although the combination procedure changes the temporal correlation in the ZTD residuals, it neither affects its spatial correlation structure nor its time-variability, for which an annual modulation is observed for stations up to 1,000 km apart. The main spatial patterns in the ZTD residuals also remain identical. Finally, we compare two GOP solutions, one of which only differs in the modeling of non-tidal atmospheric loading at the observation level, and conclude that its modeling has a negligible effect on ZTD values.
      PubDate: 2022-11-08
       
  • BDS and GPS side-lobe observation quality analysis and orbit determination
           with a GEO satellite onboard receiver

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      Abstract: Abstract Multi-GNSS combination can alleviate problems associated with GNSS-based geostationary earth orbit (GEO) satellite navigation and orbit determination (OD), such as GNSS availability and observation geometry deterioration. However, only GPS has been widely applied and investigated in GEO missions, whereas GEO OD with BDS requires further exploration. The Chinese GEO satellite TJS-5, equipped with a GPS and BDS-compatible receiver, is the first GEO mission that tracks both BDS 2nd and 3rd generation satellites since BDS global deployment. With the TJS-5 real onboard data, we evaluate BDS side-lobe signal performance and the BDS contribution to GEO OD. Due to transmit antenna gain deficiencies in the side lobes, BDS shows a worse tracking performance than GPS with an average satellite number of 4.3 versus 7.8. Both GPS and BDS reveal inconsistency between carrier-phase and code observations, which reaches several meters and significantly degrades post-dynamic OD calculation. We estimate the consistency as a random walk process in the carrier-phase observation model to reduce its impact. With inconsistency estimated, the post-fit carrier-phase residuals decrease from 0.21 to 0.09 m for both GPS and BDS. The OD precision is significantly improved, from 1.95 to 1.42 m with only GPS and from 3.14 to 2.71 m with only BDS; the GPS and BDS combined OD exhibits the largest improvement from 1.74 to 0.82 m, demonstrating that adding BDS improves the OD precision by 43.3%. The above results indicate that the proposed carrier-phase inconsistency estimation approach is effective for both GPS and BDS and can achieve an orbit precision within 1.0 m using multi-GNSS measurements.
      PubDate: 2022-11-06
       
  • An improved global grid model for calibrating zenith tropospheric delay
           for GNSS applications

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      Abstract: Abstract Accurate modeling of zenith tropospheric delay (ZTD) is beneficial for high-precision navigation and positioning. Many models with good performance have been developed for calibrating ZTD, such as the GPT3 model, which is recognized as an excellent global model and is widely used. However, certain limitations still remain in current models, such as the adoption of only single gridded data for modeling, and the model parameters need to be further optimized. In our previous research, a new approach based on the sliding window algorithm was proposed and applied to develop the GZTD-H model to address some of these limitations. However, this model is only suitable for the vertical adjustment of ZTD, not for estimating ZTD directly. In this study, an improved global grid ZTD model considering height scale factor (GGZTD-H) is derived from the initial GZTD-H model for estimating ZTD. The RMSs of the GGZTD-H model are 4.11 cm and 3.29 cm as validated by radiosonde data and IGS data, respectively. Compared with the UNB3m model and the canonical GPT3 model, the new model exhibits better performance. Moreover, three resolutions of the GGZTD-H model have been developed to reduce the quantity of gridded data delivered to users and optimize the ZTD computation process. Compared with the GPT3 model, the GGZTD-H model shows better performance with lower resolution and requires fewer model parameters for ZTD estimation, greatly optimizing ZTD computation. Users may select the best model that meets their needs in terms of the balance between resolution and accuracy. The high-precision GGZTD-H model could be used as a ZTD vertical stratification model for the vertical adjustment of atmospheric data and as an empirical model for ZTD estimation, which has potential applications in GNSS precise positioning, such as for the establishment and maintenance of the global terrestrial reference frame.
      PubDate: 2022-11-05
       
  • Retraction Note: Likelihood-based GNSS positioning using LOS/NLOS
           predictions from 3D mapping and pseudoranges

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      PubDate: 2022-11-03
       
 
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