GNSS Data Processing Research Articles

Cube: An Open-Source Software for Clock Offset Estimation and Precise Point Positioning with Ambiguity Resolution

Precise point positioning (PPP) is a prevalent, high-precision spatial absolution positioning method, and its performance can be enhanced by ambiguity resolution (AR). To fulfill the growing need for high-precision positioning, we developed an open-source GNSS data processing package based on the decoupled clock model called Cube, which integrates decoupled clock offset estimation and precise point positioning with ambiguity resolution (PPP-AR). Cube is a secondary development based on RTKLIB. Besides the decoupled clock model, Cube can also estimate legacy clocks for the International GNSS Service (IGS), as well as clocks with satellite code bias extraction, and perform PPP-AR using the integer-recovered clock model. In this work, we designed satellite clock estimation and PPP-AR experiments with one week of GPS data to validate Cube’s performance. Results show that the software can produce high-precision satellite clock products and positioning results that are adequate for daily scientific study. With Cube, researchers do not need to rely on public PPP-AR products, and they can estimate decoupled clock products and implement PPP-AR anytime.

QUALITY ANALYSIS OF SMARTPHONE GNSS OBSERVATIONS AND IMPACT ON PRECISE POSITIONING

Abstract. The use of low-cost and ultra-low-cost receivers such as smartphones and wearables has been raising these days due to their affordability and widespread availability. Along with the release of Android Version 7 in 2016, the raw GNSS measurements became accessible through the location API, which includes the GNSSMeasurement class and GNSSClock class. However, the users are required to extract the typical GNSS observations, such as pseudorange, carrier-phase, and Doppler observations, from the raw data coming from these two classes. It should be mentioned some quality concerns may arise during the conversion process from the raw GNSS measurements to the typical GNSS measurements. These quality concerns would subsequently affect GNSS data processing such as cycle slip detection, code smoothing and ultimately positioning performance. In this paper, we first analyse the quality of GNSS observations logged from smartphones. Furthermore, we address potential issues that can arise during the generation of GNSS observations. We also introduce our developed in-house software, UofC CSV2RINEX, which is designed to convert CSV files into RINEX files.

First feasibility demonstration of GNSS-seismology for anthropogenic earthquakes detection.

High-rate GNSS has been proven effective in characterising waveforms and co-seismic displacements due to medium-to-strong natural earthquakes. No application focused on small magnitude events like shallow anthropogenic earthquakes, where displacements and noise have the same order of magnitude. We propose a procedure based on proper signal detection and filtering of the position and velocity time series obtained from high-rate (10Hz) GNSS data processing with two intrinsically different approaches (Precise Point Positioning and variometry). We tested it on five mining tremors with magnitudes of 3.4-4.0, looking both at event detection and its kinematic characterisation. Here we show a high agreement, at the level of 1s, between GNSS and seismic solutions for the earthquake first epoch detection. Also, we show that high-rate multi-constellation (GPS + Galileo) GNSS can reliably characterise low-magnitude shallow earthquakes in terms of induced displacements and velocities, and, including their peak values, respectively, at the level of very few millimetres and 1-2cm/s, paving the way to the routine use of GNSS-seismology for monitoring human activities prone to cause small earthquakes and related potential damages.

PRECISION EVALUATION FOR DIFFERENT GNSS RINEX 3 USING ONLINE SERVICES AND OPEN-SOURCE SOFTWARE PPP-MANS

It is critical to evaluate the reliability of using free online processing software for Global Navigation Satellite System post-processing since the advancement of GNSS gives satellite navigation customers all over the world great benefits. AUSPOS, IBGE, Magic GNSS, CSRS-PPP, and open-source software are some of the online processing solutions being evaluated for accuracy in this study. GNSS observations from IGS were used to conduct field observations using RINEX 3 data from three stations, with an observation duration of 30 seconds. After data acquisition, it was processed with online and free software that made use of GPS, GPS, and GLONASS. When compared to coordinates obtained from reference stations, the relative differences and correctness of the coordinates generated by each piece of software were then evaluated. coordinates in the ITRF14 reference for the X, Y, and Z directions. Online GNSS processing services may be used with greater accuracy for engineering and geodetic applications and are simple to use without the need for GNSS data processing expertise.

Kinematic deformation and intensity assessment of the 2021 Maduo MS7.4 earthquake in Qinghai revealed by high-frequency GNSS

Rapid acquisition of the kinematic deformation field and seismic intensity distribution of large earthquakes is crucial for postseismic emergency rescue, disaster assessment, and future seismic risk research. The advancement of GNSS observation and data processing makes it play an important role in this field, especially the high-frequency GNSS. We used the differential positioning method to calculate the 1 HZ GNSS data from 98 sites within 1000 km of the MS7.4 Maduo earthquake epicenter. The kinematic deformation field and the distribution of the seismic intensity by using the peak ground velocity derived from displacement waveforms were obtained. The results show that: 1) Horizontal coseismic response deformation levels ranging from 25 mm to 301 mm can be observed within a 1000 km radius from the epicenter. Coseismic response deformation on the east and west sides shows bilateral asymmetry, which markedly differs from the symmetry presented by surface rupture. 2) The seismic intensity obtained through high-frequency GNSS and field investigations exhibits good consistency of the scope and orientation in the high seismic intensity area, although the former is generally slightly smaller than the latter. 3) There may exist obstacles on the eastern side of the seismogenic fault. The Maduo earthquake induced a certain tectonic stress loading effect on the western Kunlun Pass-Jiangcuo fault (KPJF) and Maqin-Maqu segment, resulting in higher seismic risk in the future.

Multipath error mitigation method considering NLOS signal for high-precision GNSS data processing

Multipath error mitigation method considering NLOS signal for high-precision GNSS data processing

Effects of 7September 5–12, 2017 solar flares on regional disturbance of Earth’s ionosphere as recorded by GNSS stations located in the Volga Federal District of the Russian Federation

The paper presents the results of estimation of the effects of September 5–12, 2017 solar flares on the regional disturbance of Earth's ionosphere according to data from a distributed network of GNSS stations located mostly in the Volga Federal District of the Russian Federation. The GNSS data processing software package we have developed is used to analyze recorded signal power and daily two-frequency phase measurements, as well as to calculate the total electron content and map the data. The results of the study show that during powerful solar flares X2.2 and X9.3 on September 6 the median value of the total electron content, calculated for the Volga Federal District, increased up to 0.25 TECU and 0.6 TECU respectively. At that time, the region of interest (40°–55° E) was sunlit. The prolonged magnetic storms on September 8 also generated noticeable ionospheric disturbances up to 0.2 TECU. At the same time, neither the solar flares nor the magnetic storms had a significant effect on the power characteristics of the recorded signals from navigation satellites in the region under study. The median carrier-to-noise ratio calculated for the region considered over the entire observation period did not differ from the values recorded under undisturbed ionospheric conditions and varied between 47–53 dBHz and 38–49 dBHz for frequencies L1 and L2 respectively.

Влияние солнечных вспышек 5-12 сентября 2017 г. на региональную возмущенность ионосферы Земли по данным ГНСС-станций, расположенных в Приволжском федеральном округе Российской Федерации

The paper presents the results of estimation of the effects of September 5–12, 2017 solar flares on the regional disturbance of Earth's ionosphere according to data from a distributed network of GNSS stations located mostly in the Volga Federal District of the Russian Federation. The GNSS data processing software package we have developed is used to analyze recorded signal power and daily two-frequency phase measurements, as well as to calculate the total electron content and map the data. The results of the study show that during powerful solar flares X2.2 and X9.3 on September 6 the median value of the total electron content, calculated for the Volga Federal District, increased up to 0.25 TECU and 0.6 TECU respectively. At that time, the region of interest (40°–55° E) was sunlit. The prolonged magnetic storms on September 8 also generated noticeable ionospheric disturbances up to 0.2 TECU. At the same time, neither the solar flares nor the magnetic storms had a significant effect on the power characteristics of the recorded signals from navigation satellites in the region under study. The median carrier-to-noise ratio calculated for the region considered over the entire observation period did not differ from the values recorded under undisturbed ionospheric conditions and varied between 47–53 dBHz and 38–49 dBHz for frequencies L1 and L2 respectively.

Precision comparison for Different GNSS PPP solution using online services and open-source software processing

In order to properly post-process data from the Global Navigation Satellite System, it is crucial to evaluate the dependability by means of online free processing tools because the development of GNSS offers satellite navigation consumers around the globe promising benefits. The purpose of the study is to assess the precision of several online processing tools, including GSIPOST, AUSPOS, IBGE, Magic GNSS, CSRS-PPP, and open-source software. Three stations' worth of RINEX 2 data were subjected to field observations utilising GNSS observations from IGS, with an observation time of 30 seconds. After that, both online and open-source software was used to analyze the collected data, using GPS and GPS and GLONASS. The relative differences and accuracy of the coordinates generated by each software were then assessed by comparison with those acquired from reference stations. coordinates in the ITRF14 standard for the X, Y, and Z directions. Online GNSS processing services don't require GNSS data processing skills and are easy to use, and provide more accurate results for engineering and geodetic uses. RINEX 3 data must be checked for better resolution.

Comparison of PPPH MATLAB based program vs Online GNSS Services

The modernization of GNSS provides promising improvements to satellite navigation users across the world, it is important to determine the reliability of using free online processing software for the Global Navigation Satellite System post-processing. The study aims at assessing the accuracy of two free online processing software, GAPS, and CSRS-PPP and Open-source software, PPPH MATLAB based software, and GNSS solutions. Field observations were carried out on data from three stations using GNSS observation from IGS with an observation period of 30 seconds the acquired data were post-processed using both online and open-source software. The coordinates generated from each software were then compared with the ones obtained from station to determine their relative discrepancies and accuracies. for GAPS and CSRS-PPP both in X, Y, and Z direction in ITRF14 reference. Online GNSS processing services are easy to use, do not require the knowledge of GNSS data processing and can be adopted for engineering and geodetic applications. Initial time must be checked for better resolution.

GNSS Horizontal Motion Field in the Beijing Plain in View of The Variation Characteristics of The 3D Deformation Field

In view of the fact that there is no unified understanding of the GNSS horizontal velocity field in the Beijing Plain and the serious land subsidence in this area, we collected GNSS data from 2011 to 2021 and Sentinel 1A data from 2017 to 2021 and conducted high-precision GNSS data processing and PS-InSAR verification in order to determine the reason for the differences in the GNSS horizontal velocity field in the Beijing Plain. The results show that, under the stable Eurasian framework, the horizontal velocity of GNSS stations in the Beijing Plain is significantly inconsistent. The velocity of all GNSS stations ranged from −1.32 to 10.41 mm/yr in the E component and from −8.83 to 3.00 mm/yr in the N component. From 2011 to 2021, there was significant uneven land subsidence in the Beijing Plain, and the maximum land subsidence rate from 2017 to 2021 reached 107 mm/yr. In analyzing the observation data of the GNSS and InSAR, we conclude that the land subsidence in the Beijing Plain will indeed affect the GNSS horizontal velocity field in the subsidence area. Under the EURA_I08 reference framework, the horizontal deformation field in the Beijing Plain is mainly caused by the tectonic activity-derived overall SEE-direction movement, accompanied by the velocity field anomaly caused by local land subsidence.

GNSS Observation Generation from Smartphone Android Location API: Performance of Existing Apps, Issues and Improvement

Precise position information available from smartphones can play an important role in developing new location-based service (LBS) applications. Starting from 2016, and after the release of Nougat version (Version 7) by Google, developers have had access to the GNSS raw measurements through the new application programming interface (API), namely android.location (API level 24). However, the new API does not provide the typical GNSS observations directly (e.g., pseudorange, carrier-phase and Doppler observations) which have to be generated by the users themselves. Although several Apps have been developed for the GNSS observations generation, various data analyses indicate quality concerns, from biases to observation inconsistency in the generated GNSS observations output from those Apps. The quality concerns would subsequently affect GNSS data processing such as cycle slip detection, code smoothing and ultimately positioning performance. In this study, we first investigate algorithms for GNSS observations generation from the android.location API output. We then evaluate the performances of two widely used Apps (Geo++RINEX logger and GnssLogger Apps), as well as our newly developed one (namely UofC CSV2RINEX tool) which converts the CSV file to a Receiver INdependent Exchange (RINEX) file. Positioning performance analysis is also provided which indicates improved positioning accuracy using our newly developed tool. Future work finding out the potential reasons for the identified misbehavior in the generated GNSS observations is recommended; it will require a joint effort with the App developers.

Processing of GNSS data in Gamit/Globk: On the example of the reference stations of the Uzbekistan network

The article presents the results of processing, a preliminary assessment of the quality of measurements, and the accuracy of the coordinates of the points of the reference network of Uzbekistan (MAGK, FARG, JARQ, and URGA). Observation data of GNSS points were processed using the GAMIT/GLOBK v.10.71 software package by applying standard procedures for position and velocities estimation relating to the ITRF2014 global reference frame. The horizontal velocities of points were compared with the latest versions of global tectonic models such as ITRF 2014, GEODVEL 2010, and NNR - MORVEL 56. Analysis of the point time series confirmed the good quality of the measurements and the accuracy of the processed coordinates in the GAMIT/GLOBK program. The calculated solutions had horizontal coordinates, uncertainties uncertainty, and repeatability, at the level of 1-3.2 mm for horizontal coordinates and 3.2-6.5 mm for height. However, the analysis of the horizontal velocities of points and comparison of the results with global tectonic models confirmed the need for further compaction of the regional satellite network, especially in the western part of the territory, taking into account the new model of modern movements of the region.

GNSS Data Processing and Validation of the Altimeter Zenith Wet Delay around the Wanshan Calibration Site

The Wanshan calibration site (WSCS) is the first in-situ field for calibration and validation (Cal/Val) of HY-2 satellite series in China. It was built in December, 2018 and began business operation in 2020. In order to define an accurate datum for Cal/Val of altimeters, the permanent GNSS station (PGS) data of the WSCS observed on Zhiwan (ZWAN) and Wailingding (WLDD) islands were processed using GAMIT/GLOBK software in a regional solution, combined with 61 GNSS stations distributed nearby, collected from the GNSS Research Center, Wuhan University (GRC). The Hector software was used to analyze the trend of North (N), East (E), and Up (U) directions using six different noise models with criteria of maximum likelihood estimation (MLE), Akaike Information Criteria (AIC), and the Bayesian Information Criteria (BIC). We found that the favorite noise models were white noise plus generalized Gauss–Markov noise (WN + GGM), followed by generalized Gauss–Markov noise (GGM). Then, we compared the PGS velocities of each direction with the Scripps Orbit and Permanent Array Center (SOPAC) output parameters and found that there was good agreement between them. The PGSs in the WSCS had velocities in the N, E, and U directions of −10.20 ± 0.39 mm/year, 31.09 ± 0.36 mm/year, and −2.24 ± 0.66 mm/year for WLDD, and −10.85 ± 0.38 mm/year, 30.67 ± 0.30 mm/year, and −3.81 ± 0.66 mm/year for ZWAN, respectively. The accurate datum was defined for Cal/Val of altimeters for WSCS as a professional in-situ site. Moreover, the zenith wet delay (ZWD) of the coastal PGSs in the regional and sub-regional solutions was calculated and used to validate the microwave radiometers (MWRs) of Jason-3, Haiyang-2B (HY-2B), and Haiyang-2C (HY-2C). A sub-regional PGS solution was processed using 19 continuous operational reference stations (CORS) of Hong Kong Geodetic Survey Services to derive the ZWD and validate the MWRs of the altimeters. The ZWD of the PGSs were compared with the radiosonde-derived data in the regional and sub-regional solutions. The difference between them was −7.72~2.79 mm with an RMS of 14.53~18.62 mm, which showed good consistency between the two. Then, the PGSs’ ZWD was used to validate the MWRs. To reduce the land contamination of the MWR, we determined validation distances of 6~30 km, 16~28 km, and 18~30 km for Jason-3, HY-2B, and HY-2C, respectively. The ZWD differences between PGSs and the Jason-3, HY-2B, and HY-2C altimeters were −2.30 ± 16.13 mm, 9.22 ± 22.73 mm, and −3.02 ± 22.07 mm, respectively.

Improved height correction model for hydrostatic mapping functions in GNSS data processing

Improved height correction model for hydrostatic mapping functions in GNSS data processing

Assessing the accuracy of online GNSS processing services and commercial software on short baselines

With the rapid establishment of free online processing services to provide users with reliable solutions, it is important to determine the reliability of using free online processing software for the Global Navigation Satellite System post-processing. The study aim at assessing the accuracy of two (2) free online processing software, AUSPOS, and CSRS-PPP and two (2) commercial software, compass post-processing, and GNSS solutions. Field observations were carried out on seven (7) control points using static GNSS observation techniques with an observation period of 1hr for three (3) consecutive days and conventional surveying using total station instruments to establish a closed traverse. The acquired data were post-processed using both online and commercial software. The co-ordinates generated from each software were then compared with the ones obtained using total station instruments to determine their relative discrepancies and accuracies. Root mean square error and T-test were used for the analysis of the result. The result obtained is (0.004m, 0.003m and 0.007m) for compass post-processing software and (0.015m, 0.012m and 0.016m) for GNSS solutions software and the online software had the Root Mean Square Error (RMSE) values of (0.025m, 0.023m and 0.027m) for AUSPOS and (0.034m, 0.037m and 0.041m) for CSRS-PPP both in X, Y, and Z direction i.e. UTM East, North and ellipsoidal height respectively. Analysis at a 5% level of significance shows no significant difference between the two methods. Online GNSS processing services are easy to use, do not require the knowledge of GNSS data processing and can be adopted for engineering and geodetic applications.

Impact of higher-order ionospheric delay on the reliability of RTK ambiguity estimation

The ionospheric delay is one of the major error sources in GNSS precise data processing. In most scenarios, only the first-order ionosphere delay was fully considered, which contributes to about 99% of the total ionosphere delay. Recent research reveals that the higher-order ionospheric (HOI) delay can also introduce up to 2 cm biases for the GPS L1 observations. This bias is generally not considered in the underlying function model and consequently, it introduces unintentional biases, which may degrade the reliability of the ambiguity estimation in long-baseline RTK. This study examined the impact of the HOI on the observations and the ambiguity estimation procedure. We considered the HOI bias in the underlying model to evaluate the unintentional HOI bias on the success rate (SR) of ambiguity estimation. The numerical results showed that the double-differenced HOI effect reaches about 7 mm in the ionospheric active period, and can affect the ambiguity estimation success rate by up to 30% in the GNSS data processing and the HOI impact is more significant when a new satellite arose. The presence of the HOI biases may change about 0.3% ambiguity fixing results. In addition, the HOI bias can also introduce several millimeters biases in positioning solutions.

Penentuan Titik IGS sebagai Titik Ikat dalam Pengolahan Data GNSS untuk Studi Geodinamika di Pulau Sumatra

Geodynamic studies on the Sumatra island generally use GNSS data. GNSS data processing using the differential method by using the IGS point as a tie point. This study aims to determine good IGS point in processing GNSS data for geodynamic studies on the Sumatra island. The data used are GNSS data from 3 SuGAr points and 20 IGS points in 2019 with DOY 061, 062, and 063. 211 GNSS data processing is carried out using different IGS points. The number of tie points used are 18, 19, and 20 IGS points. Determination of a good IGS point is based on the results of the standard deviation. The factors that cause the standard deviation value are the quality of the IGS point, distance, and temperature value. The processing results with 18 IGS points are better than 20 IGS points when using poor IGS points. The processing quality at the SuGAr point on the southern part of Sumatra Island (TJKG point) is the best compared to the other two SuGAr points. IGS points that are bad for geodynamic studies are XMIS and PBRI points because of the high standard deviation values for close distances. Good IGS points with low standard deviation values are COCO, DGAR, and LHAZ points. The low temperature value at the LHAZ point is thought to be the cause of the low standard deviation value. Â Keywords : GNSS, Standard Deviation, Precision, IGS, Differential

Very early identification of a bimodal frictional behavior during the post-seismic phase of the 2015 <i>M</i><sub>w</sub> 8.3 Illapel, Chile, earthquake

Abstract. It is well-established that the post-seismic slip results from the combined contribution of seismic and aseismic processes. However, the partitioning between these two modes of deformation remains unclear due to the difficulty of inferring detailed and robust descriptions of how both evolve in space and time. This is particularly true just after a mainshock when both processes are expected to be the strongest. Using state-of-the-art sub-daily processing of GNSS data, along with dense catalogs of aftershocks obtained from template-matching techniques, we unravel the spatiotemporal evolution of post-seismic slip and aftershocks over the first 12 h following the 2015 Mw 8.3 Illapel, Chile, earthquake. We show that the very early post-seismic activity occurs over two regions with distinct behaviors. To the north, post-seismic slip appears to be purely aseismic and precedes the occurrence of late aftershocks. To the south, aftershocks are the primary cause of the post-seismic slip. We suggest that this difference in behavior could be inferred only a few hours after the mainshock. We finish by showing that this information can potentially be obtained very rapidly after a large earthquake, which could prove to be useful in forecasting the long-term spatial pattern of aftershocks.

Sensitivity of Change-Point Detection and Trend Estimates to GNSS IWV Time Series Properties

This study investigates the sensitivity of the GNSSseg segmentation method to change in: GNSS data processing method, length of time series (17 to 25 years), auxiliary data used in the integrated water vapor (IWV) conversion, and reference time series used in the segmentation (ERA-Interim versus ERA5). Two GNSS data sets (IGS repro1 and CODE REPRO2015), representative of the first and second IGS reprocessing, were compared. Significant differences were found in the number and positions of detected change-points due to different a priori ZHD models, antenna/radome calibrations, and mapping functions. The more recent models used in the CODE solution have reduced noise and allow the segmentation to detect smaller offsets. Similarly, the more recent reanalysis ERA5 has reduced representativeness errors, improved quality compared to ERA-Interim, and achieves higher sensitivity of the segmentation. Only 45–50% of the detected change-points are similar between the two GNSS data sets or between the two reanalyses, compared to 70–80% when the length of the time series or the auxiliary data are changed. About 35% of the change-points are validated with respect to metadata. The uncertainty in the homogenized trends is estimated to be around 0.01–0.02 kg m−2 year−1.